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• Extensional rheology as a predictor for film blowing of biodegradable polymers. • Quantitative prediction of processing behaviour through degree of strain hardening. • Film blowing temperature window of biodegradable polymers enhanced through presence of partial crosslinking. Non-degradable plastic pollution, particularly from single-use packaging, poses a growing threat to the environment. To address this, biodegradable alternatives have gained attention. However, processing these biodegradable polymers into thin films for packaging applications remains a challenge due to their poor film blowing behaviour, which is neither well understood nor documented. This study presents a novel conceptual framework to help understand the underlying reasons for this poor performance. Through standardised methods, the systematic assessment of the extensional rheology behaviour of various biodegradable polymers relative to low-density polyethylene (LDPE) was characterised over a range of temperatures and strain rates, with the degree of strain hardening being recorded for each. The extensional properties were then correlated with observations from pilot-scale film blowing experiments. The findings reveal that partial crosslinking (e.g. partially cross-linked polycaprolactone) facilitates significant strain hardening behaviour across a wide temperature range and allows for film blowing. Conversely, polymers that only display strain hardening at temperatures slightly above their melting point (e.g. poly(butylene adipate- co -terephthalate) and poly(butylene succinate)) are more challenging to film blow. Additionally, polymers lacking strain hardening behaviour (e.g. poly(3-hydroxybutyrate- co -3-hydroxyvalerate), poly(3-hydroxybutyrate- co- 3-hydroxyhexanoate), poly(lactic acid), and linear polycaprolactone) present difficulties in film blowing due to excessive sagging and low melt strength, resulting in bubble instability and collapse. This research sheds light on the rheological properties that impact the processability of biodegradable polymers for practical applications, providing valuable insights for the development of sustainable plastic alternatives. [ABSTRACT FROM AUTHOR]

• LDPE materials with different origins degrade at different rates of photooxidation. • Ketone structural defects affect LDPE photostability. • Photolysis of initial ketones cancels their detrimental effect on photostability. • Initial content of unsaturation does not affect LDPE photooxidation. • A unique rate of photooxidation is observed after photolysis. The photooxidation of four different polyethylenes with various amounts of chemical defects was examined. These polyethylenes had different initial contents of vinyl and vinylidene groups, and two of them exhibited an infrared absorption band attributed to ketones. The rates of photooxidation of these four polymers were rather different, and the rates of photooxidation increased with the initial concentration of ketones. The ketones were tentatively attributed to the use of propanal as a transfer agent during polymer synthesis and were readily eliminated by photolysis (irradiation in vacuum) of the samples. The identification of butanone formed by Norrish-II reactions confirmed the presence of propanal. Notably, the four samples behaved similarly after prephotolysis and degraded at the same rate. Moreover, the rates of photooxidation after prephotolysis were found to be totally independent of the concentrations of unsaturations, which does not confirm the hypothesis of a potential influence of such groups on the initial photostability of polyethylene. [ABSTRACT FROM AUTHOR]

• Tensile strength of the multilayer was consistent up to six reprocessing cycles. • Toughness of the multilayer declined after four reprocessing cycles. • Cross-linking between LLDPE-g-MA and EVOH enhanced interfacial interaction. • EVOH gelling intensified phase separation between LDPE and EVOH. • Light stabilizer content in LDPE decreased as the reprocessing cycles increased. Multilayer plastic packaging (MPP) has attracted extensive attention due to its functionality and inherent difficulty in reclamation. One primary concern is the performance of reprocessed MPP since it inherently consists of many dissimilar polymers. This study aims to assess the effect of multiple thermomechanical reprocessing cycles on the properties of a MPP blend. Low density polyethylene (LDPE)/maleic anhydride grafted linear LDPE (LLDPE-g-MA)/ethylene vinyl alcohol (EVOH) blend was manufactured and subjected to thermomechanical reprocessing, including thermal compounding, grinding, and injection molding for six cycles to characterize the impact of thermomechanical reprocessing on the blend's mechanical, morphological, thermal, and rheological properties. The tensile strength and modulus of the reprocessed blend remained consistent throughout six cycles. A pronounced decline in elongation at break was observed after four cycles of reprocessing. Toughness, as represented by the essential work of fracture, increased steadily up to three cycles of processing, followed by a decline in the following reprocessing cycles. The main property change is possibly caused by the gelling of the EVOH in the reprocessed blend, as demonstrated by larger EVOH agglomerates in the LDPE matrix. Differential scanning calorimetry results indicated that the degree of crystallization of the EVOH phase changed with increasing reprocessing cycles, suggesting EVOH degradation. Rheological behavior in the linear viscoelastic region indicated enhanced interfacial interaction between LDPE and EVOH due to the cross-linking of LLDPE-g-MA and rigid EVOH in the early reprocessing stages. After four cycles of reprocessing, decreases in storage and loss moduli were observed, indicating the possibility of phase separation caused by gelling of EVOH. Using polymer blending to reclaim LDPE-based EVOH multilayer is promising for up to four cycles of reprocessing as shown by mechanical, thermal, and rheological behaviors. [ABSTRACT FROM AUTHOR]

• XLPE and EVA have similar thermal oxidation reactions and kinetics. • Decomposition of acetate side groups does not interact with oxidation reaction. • Differences in O2 transport properties lead to differences in oxidation profiles. • Oxidation induce consequences on both electrical and mechanical properties. • Plotting correlations allow finding several end-of-life criteria. The thermal oxidation of low-density polyethylene and poly(ethylene-co-vinyl acetate) both cross-linked with triallyl isocyanurate (respectively denoted XLPE and EVA) was studied at 165 °C in air by Fourier transform infrared (FTIR) spectroscopy, dielectric spectroscopy and uniaxial tension. Monitoring the carbonyl index throughout the exposure allowed showing that these two polymers have similar oxidation reactions, taking place on their ethylene monomers, and therefore similar oxidation kinetics. In addition, in EVA, the acetate side groups thermally decompose into several degradation products during the exposure, such as: trans-vinylene double bond, acetic acid, saturated and unsaturated γ-lactone, and methane, but without interacting with the oxidation reaction. As oxidation is diffusion controlled, it leads to the development of oxidation profiles across the sheets of about 1 mm thick of these two polymers. In addition, as the oxygen transport properties (both solubility and diffusivity) are higher in EVA than in XLPE, oxidation affects the center of the EVA sheets from the early periods of exposure, whereas it is necessary to wait for high conversion ratios of the oxidation reaction to observe the same types of chain-shaped profiles in XLPE sheets. Oxidation results in dramatic changes in functional properties (both electrical and mechanical properties) for both polymers. Before thermal aging, EVA is already a poor insulating material compared to XLPE, due to the presence of polar side groups (i.e. acetates). In contrast, EVA exhibits a higher ductility, which justifies its use as nanofillers in PE-based insulating materials in order to improve their mechanical properties. The establishment of correlations between the changes in functional properties and the progress of oxidation allows the proposal of structural, electrical and mechanical end-of-life criteria for both polymers, corresponding to critical values of carbonyl index, dielectric constant, and elongation at break, respectively. [ABSTRACT FROM AUTHOR]

• Abundant oxygen-containing groups were rapidly introduced in LDPE melts by ozone in reaction extrusion resulting in improved hydrophilicity. • Chain scission occurred in ozone treated PE at 200 °C, leading to fast relaxation time. • The decreased oxidation induction time of ozone treated PE demonstrated a vulnerability of ageing. Improving the hydrophilicity of low density polyethylene (LDPE) expends its use in blends. LDPE melt was rapidly functionalised and degraded by ozone in twin-screw extruder by varying extrusion times from one to seven and temperatures from 160 °C to 240 °C. Abundant oxygen-containing groups, such as carbonyl group (C O) at 1718 cm−1, hydroxyl group (-OH) at 3400 cm−1 and aldehyde group (-CHO) at 1740 cm−1, were generated into ozone treated PE, resulting in improved hydrophilicity. At 200 °C, ozone treated PE exhibited a high melt flow index (21.5 g/10 min) and low complex viscosity modulus due to molecular degradation. Nevertheless, cross-linking occurred at a higher temperature of 240 °C. A higher crystal peak temperature of ozone treated PE at 200 °C was attributed to the introduction of oxygen atoms. The poor thermal stability of ozone treated PE was evidenced by a lower initial decomposition temperature. The oxidation induction time of ozone treated PE at 200 °C declined from 32 min for one extrusion to 12 min for seven extrusions demonstrating a vulnerability of ageing. Increasing the extrusion times gradually enhanced the tensile modulus of the ozone treated PE at 200 °C, while raising the treatment temperature had no effect on the tensile properties. Rapid functionalisation and degradation of LDPE were successfully achieved using ozone in reactive extrusion, thus broadening the applications of ozone treated PE in composites. [ABSTRACT FROM AUTHOR]

• The observed stabilizing efficiency of a given stabilizer (HALS) depends on the irradiance. • Photooxidation rate of HALS stabilized LDPE increases when increasing the irradiance. • The increase of photooxidation rate depends on the type of HALS stabilizer. • Lifetime predictions based on exposures performed at different irradiances does not give the same lifetime for the same sample. • The predicted lifetime of HALS stabilized LDPE depends on the irradiance used. This paper concerns the experimental analysis of the effect of irradiance on the photooxidation of low-density polyethylene (LDPE) stabilized with different HALS. Infrared analysis in transmission mode was used to monitor the extent of oxidation provoked by the exposure of thin samples (100 µm thick) in a SEPAP MHE unit (Atlas/Ametek) at two different irradiances (90 W. m −2 and 300 W. m −2 between 300 and 420 nm). The temperature of the samples was maintained constant in order to focus on the impact of irradiance on the kinetics, without interfering with the temperature. The intended goal was to characterize the effect of the irradiance in accelerated testing and the consequences on the lifetime prediction. Previous results obtained in the case of unstabilized LDPE samples showed that no acceleration was obtained when increasing the irradiance from 90 W. m −2 and 300 W. m −2 while keeping the temperature constant. In the case of the stabilized samples, the results presented in the present article show that the rates of photo oxidation tended to increase when increasing the irradiance. However, the ratio of these rates never reaches the ratio of the irradiances, and these ratios depends on the stability of the samples. [ABSTRACT FROM AUTHOR]

Four processing methods were employed to control the localization of intumescent flame-retardant (IFR) and clay in linear low-density polyethylene/nylon 6 (LLDPE/PA6) blends and the effect of IFR and clay localization in blends on flame retardancy was investigated. The results obtained from the LOI and UL-94 tests showed that the flame retardancy in the blends with clay localization in the LLDPE phase was better than that of the blends with clay localization in the PA6 phase. Cone calorimeter test results demonstrated that IFR localization in the PA6 phase caused lower peak heat release rate (PHHR) than in the LLDPE phase. The combined effect resulted in the best flame retardancy exhibited in the blends with localization of IFR in the PA6 phase and clay in the LLDPE phase in comparison with the blends with other localization of IFR and clay. Scanning electron microscopy showed that clay localization in the LLDPE phase and IFR localization in the PA6 phase promoted the formation of an integrated and highly expansive char layer. It is believed the results of the study provide the references for optimizing the flame retardancy of polymer blends. [ABSTRACT FROM AUTHOR]

This study progresses our earlier studies and takes the performance characteristics of a 1:1 Irganox 1010: Irgafos 168 combination at 1000 ppm each through multiple extrusion processes in a metallocene LLDPE (mLLDPE) investigating for the first time the role of a broad range of calcium and zinc stearates based on animal vs vegetable origins of the stearine function. In this case performance was assessed using Melt Flow Rate (MFR) coupled with HPLC to determine not only the additive depletions after processing but also the rate of production of the phosphite to phosphonate. Comparative control studies were also undertaken on the single use of the separate antioxidants. Both stearates influenced the activity of the antioxidants in particular their consumption. A greater consumption after the third and fifth extrusion was observed with metal stearates produced from the vegetable stearine. Moreover, zinc stearates seemed to provide a greater detrimental effect than calcium stearates. Hydroperoxide analysis on the stearates confirmed the animal stearine to contain higher levels of peroxides which may contribute toward the higher activity. The optimisation of the thermal stabilisation of the metallocene polyethylene (mLLDPE) has also been investigated in this study. Several conditions of stability were determined for the determination of the optimal antioxidant (phenol:phosphite) ratio. The main parameter was high melt stability for a maximum processing stability of the final package via DSC analysis (OIT) coupled with assessments of embrittlement time (oven ageing) and yellowness index. Long-term stability against thermo-oxidation was considered coupled with a consideration of their hydrolytic stability as a complicating factor. In this work the (phenol/phosphite) antioxidant formulations with two different phenolic antioxidants (Irganox 1010, Irganox 1076) and six different phosphite antioxidants (Irgafos 168, Irgafos P-EPQ, Adekastab PEP-8, Adekastab PEP-36, Adekastab PEP-24G, Adekastab HP-10) were assessed at different levels taking into account the various criteria for optimal performance providing hitherto useful information than many prior studies on 1:1% ratios i.e. how much phosphite is required for optimal activity. A question often posed in the field with the results concluding an interesting unified optimum ratio of 4:1 (for most antioxidants studied) taking into account all the critical parameters. [ABSTRACT FROM AUTHOR]

Raman spectroscopy has been used to reveal the microscopic structural changes of low-density polyethylene under ultraviolet irradiation. The fraction of non-crystalline consecutive trans chains (the molecular chains in the trans conformation separate from the orthorhombic crystalline phase) drastically decreases at ∼600 h, together with a decrement in the molecular weight and an increment in the crystallinity owing to chemicrystallization. This suggests that short trans chains are prolonged to form consecutive trans chains before chemicrystallization. Moreover, gradual increases of the stretching and compression stresses are observed on the trans and amorphous chains, respectively. These conformational changes are detected by Raman spectroscopy even in the early stage of photodegradation. Chemicrystallization at ∼600 h is accompanied by structural changes, such as shortening of the interchain distance of the lamellar crystals and thinning of the amorphous layer, which induce formation of surface cracks on the macroscopic specimen. [ABSTRACT FROM AUTHOR]

The production of composites from recycled thermoplastic polymers and natural fibers has been an interesting alternative to generate polymeric materials of low cost, with sufficient properties for application and environmentally adequate. The aim of the present study was to evaluate the effects of the accelerated photochemical aging on properties of a composite produced from recycled low-density polyethylene (LDPE) with pine wood waste (PWW) in the presence of coupling agent. The oxidation, performance of mechanical properties and surface changes of the LDPE and LDPE/PWW composite were monitored at different times of aging. It was observed that LDPE/PWW composite presented a higher resistance to the accelerated photochemical aging than unfilled LDPE, mainly due to the better performance of the mechanical properties of elongation at break and tensile strength, showing that the presence of natural fibers from PWW lead to the stabilization of the polymeric matrix of LDPE. [ABSTRACT FROM AUTHOR]

• Silylamines and siloxyamines thermally dissociate into free radicals that exhibit fire proofing effect. • Silylamines and siloxyamines provide flame retardancy as standalone additives in PP. • Silylamines and siloxyamines exhibit synergistic effects with traditional phosphorous flame retardants to afford UL-94 V0 ratings in PP, LLDPE and epoxy resins. A series of innovative flame retardants containing N-Si and N-O-Si bonds have been synthesized. Their chemical structures were verified by nuclear magnetic resonance (NMR) spectroscopy and thermal stabilities determined by thermogravimetric analysis (TGA). The results indicate that their thermal and hydrolytic stabilities could be adjusted by fine tuning their silylamine (N-Si) and siloxyamine (N-O-Si) skeletons. Thus, the substituents bonded to the phthalimides, such as diphenylmethylsilyl, dimethylphenylsilyl, diphenyl‑ tert -butylsilyl, triisopropylsilyl or diphenylmethylsiloxy; whichever was attached to the imide played a significant role on its thermal and hydrolytic properties. Upon thermal dissociation, the N-Si and N-O-Si compounds were shown to yield aminyl, silyl and oxygen-centered radicals that provided fire proofing effect in polypropylene (PP) films alone and a synergistic effect in combination with conventional phosphorous flame retardant in PP, linear low-density polyethylene (LLDPE) and epoxy resins (EP). Their efficacy as flame retardants alone in thin PP films were evaluated according to the DIN4102-B2 test. Both N-Si and N-O-Si significantly slowed down the burning of PP films. Moreover, their potential as adjuvants with a conventional phosphorous based flame retardant, i.e., spirocyclic phosphonate (AFLAMMIT® PCO 900) in PP and EP resins was evaluated according to the UL-94 V fire standard. A synergistic effect was observed when the phosphorous flame retardant was combined with either N-Si or N-O-SI containing compounds, since none of the flame retardants by themselves could provide V-0 rating in the UL94-V test in PP, LLDPE or EP resins even at much higher loadings. The thermogravimetric analysis carried out under inert atmosphere revealed enhanced and earlier onset of decomposition and thermal activation of phosphorous based flame retardant in the presence of N-Si or N-O-Si in comparison to spirocyclic phosphonate, N-Si or N-O-Si used alone, respectively. The interaction of the phosphorus flame retardant with N-Si was verified by 31P NMR. [ABSTRACT FROM AUTHOR]

This article reports a study of the preparation of nanosilica-immobilized antioxidant (SiO 2 -APTMS-AO) and the thermal oxidative stability of low density polyethylene (LDPE) nanocomposites containing SiO 2 -APTMS-AO. SiO 2 -APTMS-AO was prepared based on the fumed nanosilica which was firstly modified with an aminosilane coupling agent and then reacted with 3,5-Di- tert -butyl-4-hydroxybenzoic acyl chloride. Infrared spectroscopy, X-ray photoelectron spectroscopy and thermogravimetric analysis measurements confirmed that the antioxidant group was chemically immobilized onto nanosilica. LDPE/silica nanocomposites were prepared by melt mixing and then pressed into different films. The thermal oxidative stability of the nanocomposites was evaluated by thermogravimetric analysis in air atmosphere, oxidation induction time (OIT) and long-term accelerated thermal aging. The results showed that the SiO 2 -APTMS-AO can significant improve the thermal oxidative stability of LDPE nanocomposite. Because SiO 2 -APTMS-AO is based on inorganic nano-filler, in comparison to organic antioxidants, it might have advantages in thermal stability and migration stability during processing and application. [ABSTRACT FROM AUTHOR]

A photodegradable Low Density Polyethylene-Titanium dioxide (LDPE-TiO 2 ) nanocomposite film was prepared, and its evaluation considers the partial modification of the surface of the particle using Hexadecyltrimethoxysilane (HDTS) as functionalizing agent under Ultraviolet (UV) radiation. Reaction efficiency of the nanoparticles was evaluated with Thermogravimetric (TGA) and infrared analysis (FT-IR). Nanocomposites were prepared by a melt blending technique; using a twin-screw extruder, each nanocomposite film was thermoformed into different shapes for further evaluation. Scanning Electron Microscopy (SEM) was utilized to determine the size and distribution of nanoparticles in the polymer. Experimental results indicate that surface modification increases the degree of dispersion while decreasing the particle size, enhancing the particle's compatibility with the polymer matrix. Photocatalytic degradation was assessed through accelerated degradation weathering in a chamber under UV radiation to assess the performance of photocatalytic degradation. These tests indicated, that the particle's homogeneity of dispersion and size reduction by functionalization allows for homogeneously degraded surfaces (SEM) to generated a greater abundance of oxidized groups in the sample compared with unfunctionalized sample. [ABSTRACT FROM AUTHOR]

The synergistic effect of melamine salt of chitosan phosphate (MCHP) and organic modified montmorillonite (OMMT) on the thermal stability and flammability properties of linear low density polyethylene (LLDPE) was studied. MCHP was synthesized by reaction of chitosan phosphate with melamine. OMMT was formed by the reaction of cetyl trimethyl ammonium bromide (CTAB) with sodium montmorillonite. The structures of MCHP and OMMT were characterized by FTIR and 1 H NMR. The thermogravimetric analysis of various LLDPE composites showed that the addition of OMMT to MCHP effectively improved the thermal stability of LLDPE and increased the char residues. The flammability properties of LLDPE composites demonstrated that addition of 1 wt% OMMT to 30 wt% MCHP promoted achieving V-0 rating in UL-94 test. Moreover, it participated remarkably in decreasing the peak of heat release rate (pHRR), total heat release (THR), CO and CO 2 emissions, and fire growth index (FGI). This indicated that addition of OMMT/MCHP reduced the fire risks of LLDPE. The digital photographs and SEM images of char formed after cone calorimeter test showed that addition of 1 wt% OMMT with MCHP promoted the formation of coherent and compact char layer. [ABSTRACT FROM AUTHOR]

Lignin extracted from black liquor was co-pyrolyzed with three kinds of plastic polymers (low density polyethylene (LDPE); polycarbonate (PC); polystyrene (PS)), in order to investigate the effect of plastic polymers on the distribution of pyrolysis products (especially monomeric aromatic compounds). TG-FTIR and Py-GC/MS were employed to understand the thermal behavior and identify the typical products from the pyrolysis of individual samples and their mixtures (mass ratio for the mixture: 1:1). For TG-FTIR analysis, the thermal decomposition behavior of lignin-PC mixture exhibits notable difference between the experimental and estimated results over that of lignin-PS mixture and lignin-LDPE mixture. The apparent activation energy for the main conversion zone of co-pyrolysis of lignin with PC (73.08 kJ/mol) is lowest among those of the lignin-plastic mixtures (180.17 kJ/mol for lignin with LDPE and 179.91 kJ/mol for lignin with PS mixtures), suggesting the strongest interaction between lignin and PC. The H 2 O produced by the decomposition of lignin at low temperature may promote the hydrolytic reaction of PC and the release of CO 2 . The production of several aromatic compounds assigned to lignin pyrolysis was suppressed by the addition of PC or LDPE, while the formation of monomer aromatic hydrocarbons was notably promoted during the co-pyrolysis of lignin with PS. [ABSTRACT FROM AUTHOR]

• Photo-oxidation effectively imposes deterioration & oxidation of LLDPE/LDPE (PE) film in comparison to thermal oxidation. • Stimulated enriched culture induces increased PE oxidation post abiotic treatment. • Glucose effectively stimulates microbes for enhanced oxidation of LLDPE/LDPE film. • Variability of PE oxidative by-product conceptualizes effective use of PE degraders. Polyethylene (PE), designed to be a packaging film with a short usage life cycle, is dominantly contributing to plastic waste. Here, the preliminary degradation of packaging PE film composed of a blend of LLDPE and LDPE has been investigated. A two-stage process of oxidation, linking abiotic and biotic treatment using enrichment cultures derived from the landfill site of the Deonar dumping ground, was employed to escalate the degradation process. The primary effects of abiotic aging on LLDPE/LDPE film were prominent in natural weathering conditions than thermal aging, resulting in the formation of oxidized functional macromolecules. Further, the enrichment cultures were potentially able to increase the oxidation level of naturally weathered film, detected by increased carbonyl peaks in the ATR-FTIR spectra. Also, the biotic aging concomitantly results in the reduction in water contact angle (WCA), demonstrating the deterioration in the surface property of LLDPE/LDPE film. Additionally, the stimulated enrichment cultures showed a significant variation in oxidation peaks of weathered film. The ATR-FTIR spectrum of the treated film reveals that the glucose-stimulated enrichment cultures (LPG) exhibited increased carbonyl peak intensity whereas yeast extract enrichment cultures (LPYE) showed increased intensity for the –C=C– unsaturated group. A dense biofilm layer with extracellular polymeric substances (EPS) attached to the LLDPE/LDPE surface, as indicated through SEM analysis, confirms microbial growth and utilization of PE material. Further, the bio-oxidation and degradation of LLDPE/LDPE film were verified using Gas chromatography-mass spectrometry (GC-MS). The GC-MS analysis confirms the presence of compounds having short linear hydrocarbon chains with alcohol and ester groups. These results demonstrate the degradation of LLDPE/LDPE packaging PE film in suitable abiotic conditions with emphasis on the enrichment culture's dependability for efficient biotic oxidation. Thus, the approach can be used to develop methods to alleviate the environmental pollution caused by plastic waste. [ABSTRACT FROM AUTHOR]

• Impact of compatibilization strategies of PE/PCL blends. • PE structure modified by thermo-oxidation of PE/pro-oxidants blends. • Uniform morphology of PE/pro-oxidants/PCL blends indicating high compatibility. • Strong effect of pro-oxidants on thermal degradation of PE/PCL blends. • Reduced crystallinity and lower thermal stability favor degradation. Low density Polyethylene (designated hereafter as "PE") is known for its inactivity, durability and resistance to degradation. For this reason adding pro-oxidants as additives in PE matrix could be efficient to elaborate a material designated as Ox-PE, exhibiting chemical reactivity. This modification could lead to an enhancement of compatibility between Ox-PE and other functionalized polymers. This approach has been exploited in this report to elaborate blends of Ox-PE with poly (ε-caprolactone) (PCL), a biodegradable polymer. Fourier Transform InfraRed spectroscopy (FTIR), Scanning Electron Microscopy (SEM) and thermal characterization by DSC, TGA were applied to investigate structural and thermal properties of PE/PCL (75/25 wt%/wt%) blends, compatibilized with 1 Phr and 5 Phr of Ethylene-co-Glycidyl MethAcrylate (EGMA) copolymer or with a Ox-PE/PCL mixture. Structural observations of the PE75/PCL25 blend by SEM revealed a phase separated morphology indicating incompatibility between PE and PCL. This was also confirmed by FTIR spectroscopy where no changes were noticed concerning the characteristic bands of either PE or PCL. Incorporating EGMA in the PE75/PCL25 blend resulted in reduced particle sizes of the dispersed PCL phase in the PE matrix confirming the reaction of epoxy groups of EGMA with hydroxyl end-groups of PCL at the interface. Regarding the thermal behavior, all PE/PCL blends exhibited an intermediate response between that of PE and PCL homopolymers. Interestingly, a high degree of compatibility was achieved for the Ox-PE75/PCL25 blend, together with a lower thermal stability compared to PE75/PCL25. [ABSTRACT FROM AUTHOR]

• Controlling functionalisation of molten low density polyethylene (LDPE) using ozone was achieved. • Oxygen-containing groups were generated into ozonized PE (OPE) to improve hydrophilicity of OPE. • A slight degradation of OPE occurred at mild condition (below 220 within 2 h). • Cross-linking structure was formed after further ozonation (beyond 240 ℃ over 4 h). • The crystallinity of OPE decreased while thermal stability of OPE enhanced due to cross-linking structure. High-value recycling petroleum-based polyethylene (PE) can effectively reduce carbon emissions and promote a circular economy. This study proposed a new method for functionalisation of low density polyethylene (LDPE) matrix at gas-liquid interface. The controlled functionalisation of LDPE at molten state was successfully achieved using ozone by altering reaction parameters. After ozone treatment, functionalised groups such as ketone (C O), ether (C O C) and carboxyl groups (-COOH) were generated in ozonized PE (OPE) confirmed by FTIR and XPS. The contact angle with water dropped from 99 ° of pristine PE to 85.4 ° of OPE, which demonstrated that the hydrophilicity of OPE was improved significantly. The degree of ozonation was sensitive to temperature. A slight degradation of PE predominantly occurred under the mild condition (below 220 ℃ within 2 h) while the cross-linking structure was primarily generated after further oxidation (beyond 240 ℃ over 4 h), which revealed that functionalisation of OPE could be controllably achieved. Due to the formation of cross-linking structure, the crystallinity of OPE decreased from 33.8 % to 11.0 %. Meanwhile, the residue weight of OPE had a slight increase while its activation energy of thermal degradation reduced. Therefore, the functionalisation of PE using ozone is a promising technical and environmental-friendly approach to upcycle PE in the future. [Display omitted] [ABSTRACT FROM AUTHOR]

Sheets of low-density polyethylene (LDPE) were subjected to photo-oxidation in the presence of air using a xenon lamp to irradiate the samples for times between 1 day and 6 weeks. The formation of long-chain branching (LCB) up to one week of degradation and the competition between chain scission and crosslinking at longer periods of radiation were investigated by rheological characterization, Fourier transform infrared spectroscopy, and the solvent extraction method (Rolón-Garrido and Wagner. Polym Degrad Stabil 2014, 99:136, Rolón-Garrido and Wagner. J Rheol 2014, 58:199). In the present contribution the same samples are studied by size exclusion chromatographic characterization using triple detection (concentration, light scattering and viscosity). The gel content is determined by filtration followed by the analysis of the soluble polymer fraction. The influence of photo-oxidation time on the molecular weight distribution (molar masses and polydispersity), the mean square radius of gyration and the intrinsic viscosity contraction factors is discussed. The results are correlated with the model parameters ( β and f max 2 ) of the molecular stress function (MSF) theory, used to describe quantitatively the rheological data in uniaxial elongation. It is verified that LCB occurs as an aside process, which up to one week of degradation dominates over chain scission, before gelation plays a critical role. It is confirmed that the model parameter β correlates with the gel content, which reflects the competition between chain scission and crosslinking, while f max 2 is found to correlate with the experimentally determined contraction factors. By comparing the data of this study with those obtained earlier for polystyrene comb melts with well defined structure, the influence of the branching frequency (i.e. the number of branch points per 1000 carbon atoms) on f max 2 becomes evident. [ABSTRACT FROM AUTHOR]

This study focuses on the stability of a polymeric Linear Low Density Polyethylene/Polyamide/Linear Low Density Polyethylene multi-layered container during long-term aging by exposure to light hydrocarbons in aviation gasoline. The containers examined and tested for this work were stored and used for different service periods, the longest of which is 10 years. During the containers' service periods, the inner LLDPE layer is exposed to avgas (aviation gasoline), and the outer LLDPE layer – to air. The aging process caused by the film interaction with avgas was examined by a variety of methods. Pb line-scan and IR spectroscopy show no evidence for the presence of small organic carbohydrate molecules originating from the avgas in the LLDPE. The viscoelastic and thermo-mechanical properties of the material were not significantly changed after 10 years. Nevertheless, DSC-OIT analysis shows a remarkable rise in oxidation rate as samples get older, presumably, as a result of antioxidants leaching out or being used up. The SEM results show the polymer to be much more prone to cracking, indicating a rise in crystallinity, as further substantiated by the results from DSC 1st heating cycle enthalpy evaluation. The 2nd DSC heating cycle results, which show no differences between samples, indicate the difference seen in the 1st heating cycle is affected by intermolecular rearrangements. Macro-mechanical properties show a remarkable stability for at least a decade, negating the aging phenomena discussed. Polyamide, as the load baring layer in the film, is probably responsible for the dampening seen in these results. In years to come, apparent oxidation will begin – most prominently in the outer layer – but probably would not compromise the structural strength of the bag, as both polyethylene layers are not the main load bearing layers. [ABSTRACT FROM AUTHOR]

The deformation mechanisms of low density polyethylene (LDPE) irradiated by 110 keV electrons with different fluences are discussed basing on the deformation behaviors and the structural evolution during uniaxial tensile deformation. The structural evolution is in-situ obtained from small angle X-ray scattering (SAXS) and wide angle X-ray diffraction (WAXD). It is found that the 110 keV electrons with low fluence change the transition strains of different regions (strain-hardening region, strain-softening region, secondary strain-hardening region, plateau in the strain-softening region and sub-stages in the second strain-hardening region) for LDPE. The 110 keV electrons with high fluence lead to disappearance of the strain-softening region and quick break of the samples. From SAXS and WAXD analyses, it is known that the 110 keV electrons have no effect on the disintegration of the original lamellae and the rotation of the lamellae, only slow down the formation of the new crystals. It is concluded that the crosslinking strengthening generated by 110 keV electrons is the dominant reason for the changes of the deformation behaviors of LDPE. [ABSTRACT FROM AUTHOR]

• Thermal oxidation of erucamide occurs in polyolefins during processing and improper storage. • The oxidation of erucamide results in several primary and secondary degradation products including off-flavor compounds. • About 16 primary and secondary oxidation products of erucamide were identified and characterized by HRMS. • This research paper describes plausible mechanisms for erucamide degradation compounds formation. Polyolefins use erucamide as one of their primary slip agents. The degradation of erucamide can occur during polymer processing and long-term storage, leading to the formation of numerous oxidation products. Erucamide degradation produces compounds that adversely affect the odor and color properties of polyolefins. The article describes the comprehensive characterization of erucamide degradation products formed in three different lots of low-density polyethylene (LDPE) using thermal desorption-gas chromatography mass spectrometry (TD-GC/MS) and liquid chromatography-high resolution mass spectrometry (LC HRMS) techniques. More than 20 volatile and non-volatile degradation compounds of erucamide were identified in LDPE. The structures of non-volatile degradants were predicted using both the molecular formula generated and MS/MS fragmentation data obtained by LC HRMS. The non-volatile and volatile degradation compounds formed in odorous LDPE resins were compared with that of the reference sample of LDPE having no odor. Further, the plausible mechanism of formation of volatile and non-volatile degradation compounds of erucamide is proposed. [ABSTRACT FROM AUTHOR]

• In rotational moulding (RM) process, polypropylene (PP) is recommended for engineering products like structural and automobile parts. • Comparative study on the creep performance shows that PP has a higher resistance to creep than the commercially used LLDPE's in RM. • High crystallinity, narrow MWD makes PP stiffer than LLDPE. • Accelerated creep test using stepped isothermal method (SIM) showed good agreement with the conventional creep test results. • The model proposed can be used to predict the creep behaviour of PP and LLDPE polymers at different stress levels without the need for experiments and can be used in design of rotomoulded products where failure due to creep may be a concern. Rotational moulding industry is looking to increase its utility spectrum from simple hollow products for storage purposes to complex engineered products used in structural and automobile applications. As such applications require satisfactory performance of the products for several decades, consideration of their creep performance in design is extremely important. Off late, Polypropylene (PP) is looked upon as a preferred choice of material for such products apart from the conventional high density and linear low-density polyethylene (LLDPE) grade materials, mainly due to its excellent static mechanical properties. This study presents a comparative analysis of the creep behaviour of PP with two commercially used hexene (C6) and butene (C4) grades of LLDPE to understand the long-term performance of products made out of these materials. For this purpose, accelerated creep testing using stepped isothermal method was carried out at three commonly used stress levels of 3.5, 4, 4.5 MPa and the creep behaviour was predicted at reference temperatures of 25 °C, 40 °C, and 60 °C. To compare and validate these findings, conventional creep experiments were performed up to one year, and the creep behaviour was extrapolated using Findley's equation. Rheological studies and microstructural characterisation involving wide-angle X-ray scattering, Raman mapping, solid-state NMR, and FT-IR spectroscopy were done to correlate the above findings. The study was further extended to develop a creep model using Norton Bailey law to predict the primary and secondary creep stages. This model can be efficiently used to predict the creep behaviour in a shorter time and thus can be used in the design of engineered products where creep failure may be a concern. [ABSTRACT FROM AUTHOR]

• Covalent attachment of HALS inhibited their migration during compounding as well as improved their compatibility with polymeric matrix. • Incorporation of HALS into LDPE/POE blends caused desired UV-resistant properties. • Tensile testing results and carbonyl index measurement after degradation exhibited antiaging properties of LDPE/POE blends influenced by HALS grafting degree. Polyolefins are a commodity plastic family known as low cost and recyclable material, that has displayed high potencies for wide variety of applications, resulting from their desired chemical, mechanical, and physical properties. However, further modifications are needed to improve their properties to extend their service lifetime, weathering resistance, and photostability for use in outdoor applications, which are due to their low thermal and photo-stabilities. In this research, hindered amine light stabilizers were used to enhance the photo-stability of low-density polyethylene (LDPE). For this purpose, unsaturated 4-amino-2,2,6,6-tetramethylpiperidine (UATMPP) was prepared by amidation reaction of amine groups in amino-2,2,6,6-tetramethylpiperidine with acryloylol chloride of 10-undecenoyl chloride in presence of triethylamine and 4-dimethylaminopyridine. Fourier transform infrared (FTIR) spectroscopy and nuclear magnetic resonance (NMR) exhibited successful preparation of UATMPP. UATMPP was grafted on polyolefin elastomer (POE) through melt free radical grafting method. FTIR and NMR confirmed the successful preparation of UATMPP-grafted POE. Finally, UATMPP-containing POE was mixed by LDPE through melt compounding. The results from the calculation of carbonyl index from FTIR and tensile testing after UV irradiation exhibited desired antiaging and UV-resistant properties of LDPE/POE blends, which were influenced by grafting degree of UATMPP as well as POE content (wt%). [ABSTRACT FROM AUTHOR]

Abstract: Both MMT synthesized by hydrothermal method (Fe-OMMT) and MMT prepared by modifying MMT using Fe3+ (Fe-MMT) were used to prepare flame-retardant low-density polyethylene (FR-LDPE) together with an intumescent flame retardant (IFR). The effects of two types of MMTs on the flame retardation of FR-LDPE were investigated by different measurements. Combustion tests showed that the limiting oxygen index (LOI) of LDPE/IFR28/Fe-MMT2 was increased to 34.6 from 29 of LDPE/IFR30, and the UL-94 rating of the former reached V-2 from no rating of the latter. Cone calorimeter (CC) test demonstrated that both Fe-OMMT and Fe-MMT improved the combustion behaviors of LDPE/IFR at about 2 wt%. LDPE/IFR/Fe-MMT had a lower heat release rate (HRR), lower total heat release (THR) and more residues than LDPE/IFR/Fe-OMMT at the same loading in the range from 0.5 to 3 wt%. Scanning electron microscopy (SEM) observation showed that both Fe-MMT and Fe-OMMT could promote the formation of continuous and compact intumescent char layer in LDPE/IFR. Both CC and UL-94 tests vitrified that Fe-MMT had better contribution to IFR in fire resistance test. Thermogravimatric (TG) and Mossbauer spectrum etc. revealed that the different efficiency of Fe-OMMT and Fe-MMT should mainly be resulting from the structure difference between Fe-MMT and Fe-OMMT, in which the essential difference might be the different existing state of Fe in two types of MMTs. [Copyright &y& Elsevier]

Abstract: Sheets of low-density polyethylene (LDPE) were photo-oxidatively treated in the presence of air. Characterization methods include solvent extraction method and rheology in the melt state by shear and uniaxial extensional experiments. For photo-oxidation, a xenon lamp was used to irradiate the samples for times between 1 day and 6 weeks. Linear viscoelasticity is strongly affected by increasing photo-oxidation due to crosslinking of LDPE, as corroborated by gel fraction. For samples which were degraded for up to three days, negligible gel content was found and the non-linear parameters and of the Molecular Stress Function (MSF) model indicate that the induced increase in strain hardening is due to the formation of long-chain branching, which is overcoming chain scission. Further degradation leads the parameter to increase to values outside the experimental window, while the parameter was found to correlate with the gel content and with the trend followed by the strain hardening index. The competition between chain scission and crosslinking could also be followed in linear viscoelasticity by the change in activation energy and in the loss angle δ. From the constitutive analysis, it is noticed that, within the experimental window, time-deformation separability is confirmed for all samples, independent of the degree of photo-oxidation. It is demonstrated that the sensitivity of rheological characterization with respect to structural modifications, when combined with constitutive analysis, can be used to elucidate the effects of photo-degradation on LDPE. [Copyright &y& Elsevier]

Abstract: Fumed silica (FS) and synthetic boehmite alumina (BA) nanofillers with and without surface treatments were incorporated in 5 wt. % in low density polyethylene (LDPE) through melt blending. FS was treated using hexadecyl silane, whereas BA using octyl silane and alkylbenzene sulfonic acid. The related nanocomposites were subjected to pyrolysis gas chromatography-mass spectrometry (Py-GC-MS) and thermogravimetric analysis (TGA) under isothermal and dynamic conditions, respectively. Py-GC-MS results proved that the thermal degradation mechanism did not change in the presence of the nanofillers. The latter suppressed the formation of high molecular weight hydrocarbons and affected the relative amounts of diene/alkene/alkane fragments for each hydrocarbon fraction. Dynamic TGA scans were registered at different heating rates in air. The activation energy (E α ) of thermoxidative degradation was calculated by the Ozawa-Flynn-Wall (OFW) method at various degradation degrees. E α of the LDPE nanocomposites depended on both specific surface area and surface treatment of the nanofillers used. The former enhanced whereas the latter decreased the activation energy for the LDPE-FS nanocomposites. By contrast, E α was slightly increased for the surface treated LDPE-BA nanocomposites. [Copyright &y& Elsevier]

• The addition of nano-silica delayed the loss of HALS from the nanocomposite film. • Adding nanoclays to the stabilized film accelerated the photo-oxidative degradation. • UV stability results were in good correlation with the HALS loss rate from the films. The adverse environmental effects (UV radiation and oxidation) on polyethylene films' durability significantly shorten their service life. This work was aimed to study the influence of incorporation of nanoparticles (hydrophobic nanosilica and Na+ nanoclays) to UV stabilized films (by hindered amine light stabilizer – HALS) on sustaining their properties by delaying the loss of the HALS from linear low-density polyethylene (LLDPE) films under photo-oxidative and humid environments. Results demonstrated that the incorporation of nanoclays to the stabilized film increased the photo-oxidative degradation of the LLDPE due to enhanced loss of the HALS from the nanocomposite film. In contrast, the addition of nano-silica delayed the loss of HALS under the same harsh conditions. The slower loss of HALS was attributed to the introduction of a longer diffusion path for the HALS molecules provided by the well-dispersed hydrophobic nanosilica particles and the immobilization effect resulting from the chemical affinity between the hydrophobic nanosilica and the hydrophobic sites on the HALS molecules. The HALS's increased retention in the LLDPE/nanosilica nanocomposite film resulted in extended retention of the film's mechanical properties. [ABSTRACT FROM AUTHOR]

• Environmental conditions affect photocatalytic degradation of LDPE-TiO 2. • First report the effect of environments on degradation mechanism of LDPE-TiO 2. • Organochlorine was first observed in the debris of LDPE-TiO 2. • HO‧ in water containing NaCl attacks LDPE-TiO 2 via reaction with Cl− forming Cl. Photocatalytically degradable plastics (PDP) are promising in mitigating plastic pollution due to their high degradability. Nevertheless, the unclear impact of environmental conditions on properties of debris for PDP and the knowledge gap in the mechanism from the perspective of photogenerated reactive species' function hinder PDP's application. Here, low-density polyethylene (LDPE) containing TiO 2 (LDPE-TiO 2) was selected as representative PDP. The photocatalytic degradation performance and mechanism of LDPE-TiO 2 in water without NaCl, water with NaCl, and air were studied. Compared with water, the air resulted in a higher carbonyl index and higher molecular weight of debris from LDPE-TiO 2 whether the irradiation time was the same (120 h) or the mass loss of LDPE-TiO 2 was the same (68 ± 2%). Chloride ions in water conditions resulted in C Cl bond formation in the debris of LDPE-TiO 2 suggesting generation of organochlorine substance. In the air the photogenerated electron (e −) contributed to LDPE-TiO 2 film degradation, while in the water e − mainly underwent recombination with the photogenerated hole. In water with Cl−, HO‧ attacked LDPE via reaction with Cl− forming organochlorine substance. The effects of environmental conditions on the properties of debris and the functions of photogenerated reactive species for PDP degradation are reported for the first time in this study. The findings provide scientific support for the development of PDP technology. [Display omitted] [ABSTRACT FROM AUTHOR]

In the present study, polystyrene (PS), low-density polyethylene (LDPE), high-density polyethylene (HDPE), polypropylene (PP), and their mixture undergo intermediate isothermal pyrolysis at 450 °C, 500 °C, 550 °C, and 600 °C inside a tubular semi-continuous reactor under an inert nitrogen atmosphere. The liquid pyrolytic oil samples recovered in each case were analyzed through gas chromatography-mass spectrometry (GC–MS) and flame ionization detector (GC-FID) to identify and quantify the different products formed. It was found that polyethylenes (HDPE and LDPE) behave similarly in these pyrolysis conditions. For instance, GC analysis showed consecutive triplet series of linear aliphatic hydrocarbons at each carbon number of the alkane, 1-alkene, 1,(N-1)-alkadiene where N is the carbon number. On the other hand, PP, LDPE, and HDPE pyrolytic oil were rich in olefinic compounds. However, the case was quite different for PS. The pyrolytic oil was constituted totally of aromatic compounds ranging from mono to tri aromatic hydrocarbons. Styrene was the main product, along with other products such as styrene dimer, styrene trimer, benzene, toluene, bibenzyl, and α-methylstyrene. Results showed an increase in lighter hydrocarbons as the temperature increased, especially for styrene, where the weight fraction in the oil increased from 40 wt.% to 60 wt.%. Ultimately, a synergistic effect was observed with mixed plastic pyrolysis, yielding lighter compounds with a lower liquid quantity. In addition, the quality of the oil seems to be improved by the increase of around 10 wt.% of both aromatic and light compounds from the expected value at the expense of the heavier fraction. The computed lower heating value (LHV) for gaseous and liquid products ranged between 40 MJ/kg and 51 MJ/kg. A quick glance at the possible end use of each oil was investigated along with a principal component analysis (PCA) on the pyrolytic oil. [ABSTRACT FROM AUTHOR]

Abstract: A novel photocatalytic polyacrylamide grafted TiO2 (PAM-g-TiO2) nanocomposite was prepared and embedded into a low density polyethylene (LDPE) plastic. Photocatalytic degradation of the LDPE/PAM-g-TiO2 composite film was carried out under ambient conditions under ultraviolet light irradiation. The properties of composite film were compared with those of the pure LDPE film by measuring the changes in weight loss, carbonyl index, molecular weight, tensile strength and elongation at break. PAM-g-TiO2 embedded LDPE showed highly enhanced photocatalytic degradation. Irradiating the LDPE/PAM-g-TiO2 composite film for 520 h under UV light reduced its weight by 39.85% and average molecular weight (M w) by 94.60%, while that of pure LDPE film was only 1.03% and 69.59%, respectively. The addition of PAM-g-TiO2 brought about the good dispersion of TiO2 in LDPE matrix and improved the hydrophilicity of composite film, which were able to facilitate the degradation of LDPE. The photocatalytic degradation mechanism of the films is briefly discussed. [Copyright &y& Elsevier]

Abstract: The mechanical properties of two linear low density and low density polyethylenes containing a pro-oxidant additive were monitored during accelerated aging (60 °C in a convection oven) and weather exposure. Tearing tests (trouser) were performed for the first time in polyethylenes subjected to oxo-degradation revealing a transition from an extensible to a non-extensible material, at exposure times when standard tensile tests were not able to detect any changes in the materials. The essential work of fracture (EWF) technique was also applied and the results were in agreement with those of trouser tests. The specific essential work of fracture first increased with exposure time until the sample experienced a transition to a less ductile state where EWF was no longer applicable. EWF and trouser tear tests were more sensitive detecting the onset of degradation probably because they employ notched specimens that impose more critical stress concentration conditions than conventional tensile tests. [Copyright &y& Elsevier]

Abstract: Low-density polyethylene (LDPE) films were exposed at an altitude of 40 km over a 3 day NASA stratospheric balloon mission from Alice Springs, Australia. The radiation damage, oxidation and nitration in the LDPE films exposed in stratosphere were measured using ESR, FTIR and XPS spectroscopy. The results were compared with those from samples stored on the ground and exposed in a laboratory plasma. The types of free radicals, unsaturated hydrocarbon groups, oxygen-containing and nitrogen-containing groups in LDPE film exposed in the stratosphere and at the Earth's surface are different. The radiation damage in films exposed in the stratosphere are observed in the entire film due to the penetration of high energy cosmic rays through their thickness, while the radiation damage in films exposed on the ground is caused by sunlight penetrating into only a thin surface layer. A similarly thin layer of the film is damaged by exposure to plasma due to the low energy of the plasma particles. The intensity of oxidation and nitration of LDPE films reflects the difference of atmospheric pressure on the ground and in the stratosphere. The high-density radiation damage of the LDPE films above the ozone layer in the stratosphere is caused by primary cosmic rays as well as collision induced cosmic ray air showers, and is consistent with the measured flux of cosmic radiation. The results show, that stratospheric flights can be used to simulate the effects of space environments during interplanet space flights for the purposes of investigating the degradation of polymer materials. [Copyright &y& Elsevier]

Abstract: We demonstrate here the structural, thermal, and wettability characteristics of low density polyethylene powder before and after plasma treatments. The plasma treatment was carried out using different working gas i.e. air, oxygen and a mixture of hydrogen and oxygen at an atmospheric pressure of 100 Pa. The plasma treatment time was kept constant at 2 min for all the specimens. Fourier transform infrared (FTIR), dynamic capillary rising using Washburn method, differential scanning calorimetry (DSC), and thermogravimetric analysis has been carried out for both pristine and plasma treated polyethylene specimens. Our study shows that there is 88% increase in the wettability after plasma treatments. Plasma treatment in air atmosphere gives the maximum wettability. Thermogravimetric analysis (TGA) investigation shows plasma treatment in the H2 + O2 mixture atmosphere gives maximum thermal stability whereas the DSC results reveal the lowest crystallinity for plasma treatment in air atmosphere. The lowest latent heat of fusion (154 J/g) calculated from the melting curve of DSC is observed for LDPE treated in air atmosphere. The FTIR spectroscopy of the plasma-treated LDPE powder reveals that plasma treatment introduces polar group on the LDPE surface leading to the increased surface free energy and surface active sites. The CH2 concentration increases after plasma treatments. [Copyright &y& Elsevier]

Abstract: This article investigates the influence of a pro-oxidant additive on the accelerated and environmental degradation of linear low density polyethylene (LLDPE) and low density polyethylene (LDPE). Extruded cast films (100 μm) were prepared with various amounts of a pro-oxidant (a so-called “Oxo” additive) (0%, 1% and 2% w/w). The films were subjected to either environmental weathering or air oven aging (60 °C) tests for 260 days. The chemical and physical changes induced by aging were monitored by: Gel Permeation Chromatography (GPC), Fourier Transform Infrared Spectroscopy (FTIR), Differential Scanning Calorimetry (DSC), Successive Self-nucleation and Annealing (SSA) thermal fractionation and tensile tests. Neat PE samples did not exhibit significant changes during the period evaluated. Crystallinity obtained from standard DSC tests during accelerated degradation exhibited variations due to a combination between annealing and recrystallization after chain scission. For both accelerated and environmental degradation a complete loss of mechanical properties was obtained although at different exposure times. SSA was shown to be the most sensitive technique applied since it evidenced early structural changes during degradation in LLDPE and LDPE that were undetected by GPC, tensile tests (i.e., strain at break) or FTIR at identical exposure times. SSA tests after accelerated degradation revealed that LLDPE linear sequences in between branching points are substantially more affected at longer exposure times than those in LDPE, a result that may imply differences in degradation mechanisms during the later stages of the degradation process. [Copyright &y& Elsevier]

Abstract: Low density polyethylene (LDPE) was exposed to one hundred (100) consecutive extensive extrusion cycles to simulate mechanical recycling. Collected samples were characterized by means of small amplitude oscillatory measurements to investigate rheological properties, by gel permeation chromatography (GPC) to measure molecular weight, and with differential scanning calorimetry (DSC) to study thermal properties. Finally, solid time-dependent mechanical properties were characterized by measuring creep compliance. The results show that simulated recycling did not significantly change the melting and crystallization temperatures of LDPE. However, results from rheological measurement, crystallinity, creep measurements and GPC suggest that thermal degradation and gelation of LDPE occur after extensive extrusion which leads to simultaneous chain scission and crosslinking of the polymer chains. It can be concluded that processability, measured by rheological parameters at high frequency and durability of LDPE measured by creep compliance, are only affected after the 40th extrusion cycle. These observations correspond to the molecular changes of LDPE measured through GPC, MFI and crystallinity calculations obtained from DSC measurements. [Copyright &y& Elsevier]

Abstract: The influence of the octene content on the photodegradation behaviour of ethylene–octene copolymers (EOCs) was revealed by investigating the photooxidation of low density polyethylene (LDPE) and EOCs with different octene contents through a series of characterisation methods. LDPE was very sensitive to ultraviolet light and the photostabilities of EOCs decreased with increasing octene concentration. The photodegradation of all samples produced hydroxyl, carbonyl and vinyl groups. The ease of chain crosslinking and scission was increased as the octene content rose. Crosslinking predominated in late irradiation period of LDPE while chain scission was dominant in that of EOCs. Annealing and chain scission promoted the secondary crystallisation of the crystallisable chain segments. Chain scission enhanced the crystallisation ability of the irradiated EOCs while it decreased that of the weathered LDPE. The photostabilities of crystals could be ranked as follows: the chain-folded lamellar crystals>the bundled crystals>the fringed micellar crystals. The thermal stabilities and mechanical properties of samples decreased with increasing irradiation time and the decreasing extent was correlated with the comonomer content. [Copyright &y& Elsevier]

Abstract: The present work aims at evaluating the behaviour of various grades of high and low density polyethylene subjected to continuous injection moulding operations. It is based on a wide range of experimental techniques that allowed the establishment of relationships between the observed property changes and the structural modifications developed in the polymers. The study confirmed the coexistence of two distinct degradation mechanisms, crosslinking and chain scission, that occur due to thermo-oxidative reactions arising during the different injection moulding stages. The relative importance of these two mechanisms depends on the material structure and on the processing conditions used. It was also possible to confirm that the polyethylenes with lower molecular mass show low sensitivity to degradation during reprocessing. Furthermore, the more branched polymers (as is the case of LDPE) also proved to be less sensitive to thermo-degradation phenomena. Overall, it was concluded that the primary recycling of polyethylene, if performed under well controlled conditions, will lead to only minor material property losses. [Copyright &y& Elsevier]

Abstract: High density polyethylene (HDPE), linear low density polyethylene (LLDPE), and isotactic polypropylene (PP) containing antioxidant additives at low or zero levels were extruded and blown moulded as films. An HDPE/LLDPE commercial blend containing a pro-oxidant additive (i.e., an oxo-biodegradable blend) was taken from the market as supermarket bag. These four polyolefin samples were exposed to natural weathering for one year during which their structure and thermal and mechanical properties were monitored. This study shows that the real durability of olefin polymers may be much shorter than centuries, as in less than one year the mechanical properties of all samples decreased virtually to zero, as a consequence of severe oxidative degradation, that resulted in substantial reduction in molar mass accompanied by a significant increase in content of carbonyl groups. PP and the oxo-bio HDPE/LLDPE blend degraded very rapidly, whereas HDPE and LLDPE degraded more slowly, but significantly in a few months. The main factors influencing the degradability were the frequency of tertiary carbon atoms in the chain and the presence of a pro-oxidant additive. The primary (sterically hindered phenol) and secondary (phosphite) antioxidant additives added to PP slowed but did not prevent rapid photo-oxidative degradation, and in HDPE and LLDPE the secondary antioxidant additive had little influence on the rate of abiotic degradation at the concentrations used here. [Copyright &y& Elsevier]

Abstract: LDPE films have been coated with single or bi-layer hybrid coatings formed through sol–gel reactions in order to improve their thermo-oxidative resistance. Different chemical compositions of the coating were investigated which differ either in the amount of the inorganic phase (silica deriving from tetraethoxysilane) or in the organic component (either alkoxy silane functionalized polyethylene–poly(ethylene glycol) diblock copolymers or poly(vinyl alcohol)). The thermo-oxidative stability of the coated films thus obtained has been assessed by means of isothermal differential scanning calorimetry (DSC) and isothermal thermo-gravimetric analysis (TGA) under accelerated conditions, i.e. at high temperatures in pure oxygen flow. Conventional ageing in air at lower temperature, slightly above the in-service one, has also been carried out. The obtained data show: a) a general improvement of the thermal-resistance for the coated LDPE samples; b) a particularly high thermal-resistance for LDPE coated with a bi-layer coating with pure silica in the top layer; c) the effectiveness of the accelerated techniques in qualitatively assessing the thermo-oxidative resistance of the coated polymeric systems. [ABSTRACT FROM AUTHOR]

Abstract: The photodegradation behaviour of ethylene-vinyl acetate copolymer (EVA)/low density polyethylene (LDPE) composite containing four different types of titanium dioxide (TiO2) was investigated through colour difference, Fourier transform infrared (FTIR) spectroscopy, differential scanning calorimetry (DSC), thermogravimetric analysis (TGA) and mechanical tests. The results showed that the performance losses of composites were qualitatively correlated with the degradation degree. The vinyl acetate (VA) groups in EVA were sensitive to UV light and the photodegradation mainly occurred in the amorphous region. The chain scission and annealing effect facilitated the secondary crystallization of composites. The heterogeneous nucleation effect of TiO2 on the crystallization of composites was related to the particle size of TiO2. The micro rutile TiO2, micro anatase TiO2 and their mixture (rutile/anatase=13/87) exhibited a photo-stabilising effect, while the nano mixed crystals TiO2 (rutile/anatase=20/80) had an opposite effect. [Copyright &y& Elsevier]

Abstract: Two low density polyethylene films, which contained pro-oxidant additives, where investigated, one of them containing micro-milled calcium carbonate filler. Both materials were subjected to controlled thermal oxidation, the oxidation was obviously retarded in the filler-containing sample. Following this, the biodegradability of samples pre-oxidized for 40 and 80 days was investigated. The levels of carbon mineralization reached 13% and 16% for the 40 and 80 days pre-oxidized polyethylene containing filler, respectively, after approximately 16 months in a soil environment at 25 °C, and both types of sample were mineralized to about 19% in compost environment at 58 °C during the same period. The sample not containing filler was mineralized to about 7% in soil after 13 months, and about 23%, after 8 months in compost. Scanning electron microscopy revealed dense colonization of the sample surfaces in both soil and compost. The data presented here provide clear quantitative evidence that part of the polyethylene material was biodegraded. [ABSTRACT FROM AUTHOR]

Abstract: Photodegradation of low density polyethylene (LDPE) containing nano-particulate ZnO has been studied using FTIR to follow the development of oxidation products in the polymer film and to monitor carbon dioxide evolved as a principal product of oxidation. The degradation behaviour of ZnO-free LDPE has been compared with that of compounds containing 0.25% and 0.75% ZnO and these results are compared with those obtained using similar films containing nano-particulate TiO2. Under UV exposure, the presence of ZnO accelerated the development of carbonyl groups and CO2 production. The carbonyl group development was more rapid when TiO2 was used whereas ZnO caused greater CO2 generation. Carbonyl group development seemed to correlate better with the reduction in mechanical properties whereas CO2 generation correlated better with weight change measurements. The influence of ZnO on the oxidation pathways in LDPE is discussed; it is proposed that photo-oxidation is relatively much more likely to occur at terminal sites (rather than at pendent sites) when ZnO is present. [ABSTRACT FROM AUTHOR]

Abstract: Synergistic effects of sunlight exposure, thermal aging and fungal biodegradation on the oxidation and biodegradation of linear low density poly(ethylene) PE-LLD films containing pro-oxidant were examined. To achieve oxidation and degradation, films were first exposed to the sunlight for 93 days during the summer months followed by their incubation with fungal strains previously isolated from the soil based on the ability to grow on the oxidized PE-LLD as a sole carbon source. Some films were also thermally aged at temperatures ranging between 45°C and 65 °C, either before or after fungal degradation. Films with pro-oxidant additives exhibited a higher level of oxidation as revealed by increase in their carbonyl index (COi). In addition to increase in the COi, films showed a slight increase in crystallinity and melting temperature (T m), considerably lower onset degradation temperatures, and a concomitant increase in the % weight of the residues. The level of oxidation observed in thermally aged films was directly proportional to the aging temperature. The PE-LLD films with pro-oxidant exposed to sunlight followed by thermal aging showed even higher rate and extent of oxidation when subsequently subjected to fungal biodegradation. The higher oxidation rate also correlated well with the CO2 production in the fungal biodegradation tests. Similar films oxidized and aged but not exposed to fungal biodegradation showed much less degradation. Microscopic examination showed a profuse growth and colonization of fungal mycelia on the oxidized films by one strain, while another spore-producing strain grew around the film edges. Data presented here suggest that abiotic oxidation of polymer''s carbon backbone produced metabolites which supported metabolic activities in fungal cells leading to further biotically-mediated polymer degradation. Thus, a combined impact of abiotic and biotic factors promoted the oxidation/biodegradation of PE-LLD films containing pro-oxidants. [Copyright &y& Elsevier]

Abstract: Extruded low-density polyethylene (LDPE) films commonly available in the market as 20-micron thick carrier bags were autoclaved, overlaid on nutrient agar plates and inoculated with BP/SU1 strain of Staphylococcus epidermis. The nutrient agar plate showed growth of the organism within two to three days. The polymer film supporting the growth of the organism showed pore formation as recorded by SEM analysis. The growth of BP/SU1 is supported by the presence of shredded LDPE as its only carbon source in inorganic salt minimal nutrient medium. The organism survives even after three months of inoculation and this is accompanied by gradual breakdown of the size of the shredded plastic as seen by light scattering. The cell-free supernatant of the organism, grown with the help of shredded plastic shows the presence of the over expressed proteins with approximate molecular weight of about 55kDa and 35kDa, through SDS-PAGE analysis. [Copyright &y& Elsevier]

Abstract: The mechanical and thermal behaviors of linear low density polyethylene (LLDPE) pipe with variation in thermal exposure time were studied. The prolongation of thermal exposure time leads to a progressive increase, until 6000 h, in tensile strength and a slight increase in hardness, while a proportional decrease in elongation at break. These results can be explained by the increase of crystallinity, followed by the increase of crosslinking density and the decrease in chain mobility due to thermal oxidation as the exposure time increases. The additional ageing to the antioxidant-depleted LLDPE pipe induces the formation of T2 endotherm, which leads to a negative effect in mechanical properties. Long-term hydrostatic pressure test result implies the existence of transition point from ductile to brittle fracture in terms of the thermal exposure time. Chemiluminescence (CL) and oxidation induction time (OIT) tests are employed to monitor the thermo-oxidative degradation of LLDPE pipe. The CL emission intensity increases with increasing with thermal exposure time. Furthermore, the OIT result suggests that after 6000 h of the thermal ageing, the depletion of antioxidant originally added in LLDPE pipe occurs. Fourier transform-infrared spectroscopy results show the increase of carbonyl (–Cdroxyl (O–H) function groups on the surface of thermally exposed LLDPE pipe. This result suggests that the hydrocarbon groups locally undergo the oxidation on the LLDPE surface due to thermal degradation. [Copyright &y& Elsevier]

Abstract: Polymeric methylene diphenyl diisocyanate (PMDI) was added as chain extender to a blend of recycled poly(ethylene terephthalate) (R-PET) and linear low density polyethylene (LLDPE) with compatibilizer of maleic anhydride-grafted poly(styrene–ethylene/butadiene–styrene) (SEBS-g-MA). Hydroxyl end groups of PET can react with both isocyanate groups of PMDI and maleic anhydride groups of SEBS-g-MA, which are competing reactions during reactive extrusion. The compatibility and properties of the blends with various contents of PMDI were systemically evaluated and investigated. WAXD results and SEM observations indicated that chain extension inhibits the reaction between PET and SEBS-g-MA. As the PMDI content increased, the morphology of dispersed phase changed from droplet dispersion to rodlike shape and then to an irregular structure. The DSC results showed that the crystallinity of PET decreased in the presence of PMDI, and the glass transition temperature (T g) of PET increased with addition of 0–0.7w% PMDI. The impact strength of the blend with 1.1w% PMDI increased by 120% with respect to the blend without PMDI, accompanied by only an 8% tensile strength decrease. It was demonstrated that the chain extension of PET with PMDI in R-PET/LLDPE/SEBS-g-MA blends not only decreased the compatibilization effect of SEBS-g-MA but also hindered the crystallization of PET. [Copyright &y& Elsevier]

Abstract: Transition metal stearates have been reported to act as effective pro-oxidants for polyethylene, even at trace concentrations. This study is an attempt to investigate the effect of the oxidation state of a metal on its pro-oxidant nature. Three metal stearates, namely manganese, iron and cobalt, in their common oxidation states (+2 and +3), were synthesized and their effect on the photo-oxidative and thermo-oxidative degradation of low-density polyethylene (LDPE) films has been investigated. Films of 70 ± 5 μ were prepared by film blowing technique, exposed to xenon arc weatherometer and air oven at 70 °C for extended time periods. The chemical and physical changes induced by this exposure were followed by monitoring the changes in mechanical properties (tensile strength and elongation at break), carbonyl index (CI), molecular weight (viscometry), MFI, density, and thermal properties. The results were analysed to explain the structural and chemical modifications taking place in the polymeric matrix as a result of aging. The studies reveal that the oxidation state of the metal did not affect its ability to initiate and accelerate degradation. The thermo-oxidative degradation in the presence of metal stearate was found to follow the order: cobalt > manganese > iron. However, iron stearate was capable of initiating photo-oxidative degradation to the same extent as cobalt and manganese, in the concentration range investigated. The results indicate that iron is primarily an effective photo-oxidant, while cobalt and manganese can act both as photo-oxidant as well as thermo-oxidant. [Copyright &y& Elsevier]

Abstract: In this work, we have investigated the intumescent behaviour of linear low-density polyethylene (LLDPE) containing calcium carbonate (chalk) treated by stearic acid. This system swells during burning and creates a protective layer when exposed to an external heat flux of 50kW/m2 in a mass loss calorimeter. This system has been fully characterized by FTIR, XRD, TGA and SEM. The carbonation/decarbonation temperatures, the swelling phenomenon and the effect of the thermal stress on the swelling have been examined. The residue is composed of a smooth surface made of chalk and CaO and a bulk of only chalk. Stearic acid allows a good dispersion of chalk particles into the LLDPE matrix, and contributes to form a cohesive network during burning when the thermal stress is high enough. A governing parameter of the intumescent effect is the particle size, which permits the formation of an insulating and cohesive mineral network during burning. [Copyright &y& Elsevier]

Abstract: Low density polyethylene (LDPE) was modified by plasma immersion ion implantation (PIII) with nitrogen ions of 20 keV. Surface energy and structural transformations were observed during storage of the modified LDPE in air after PIII, by wettability measurements and FTIR–ATR spectra respectively. The appearance of oxygen-containing groups has some kinetic stages with characteristic times from hours to days. The surface energy values attained and comparison with the kinetics of oxidation reveal that the initial changes in the surface energy of LDPE are caused mainly by free radicals and to a lesser extent by oxygen-containing groups. The final surface energies observed after the process known as hydrophobic recovery and the surface energies stabilize are attributable to oxygen-containing groups. The modified surface is “living” and an investigation of the wettability, surface energy, unsaturated and oxygen-containing groups in the surface layer of ion beam modified polymers is incomplete if the kinetics of structural transformations after modification is not taken into account. [Copyright &y& Elsevier]