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For microstructure characterization of polyolefin by separation-based techniques with infrared detector, either 1,2-dichlorobenzene (o-DCB) or 1,2,4-trichlorobenzene (TCB) is commonly selected as a dissolution solvent and mobile phase. Herein, we studied the effects of o-DCB and TCB on the comonomer detection and chemical composition distribution (CCD) by crystallization elution fractionation (CEF) with a filter-based IR detector. We first compared the detector sensitivity on methyl group content or short chain branching (SCB) in polyethylene-co-butene with varied sample concentrations in o-DCB and TCB. TCB demonstrated superior comonomer detection in the IR detector with a single linear calibration across a wide range of sample concentrations. In contrast, o-DCB displayed stronger concentration dependent methyl group response, requiring a more complex equation in the calibration. Furthermore, o-DCB provided better separation of comonomer distribution with less peak broadening and co-crystallization effects, as observed with various polyolefins, including high density polyethylene (HDPE), linear low-density polyethylene (LLDPE), polypropylene (PP), and ethylene-propylene copolymer (EP). [Display omitted] • Solvent selection (o-DCB or TCB) influences comonomer detection sensitivity, which can be addressed by a modified calibration. • o-DCB offers better separation of the comonomer distribution with minimal peak broadening and co-crystallization effects. • Solvent choice (o-DCB vs. TCB) significantly affects PP peak temperature in CCD analysis, unlike PE. [ABSTRACT FROM AUTHOR]

This investigation employed free radical melt grafting technology for the synthesis of (POE/R-LLDPE)-g-(GMA-co-St) graft copolymers. Subsequently, this graft copolymer was applied as a modifier for poly (butylene terephthalate) (PBT) resin. The effects of varying recycled linear low-density polyethylene (R-LLDPE) contents in the graft on the rheological behavior, thermal properties, mechanical properties, and toughening mechanism of PBT/(POE/R-LLDPE)-g-(GMA-co-St) blends were exhaustively explored. The findings revealed that glycidyl methacrylate (GMA) and styrene (St) were effectively grafted onto the poly (ethylene-octene) (POE) and R-LLDPE molecular chains. This process enabled the epoxy groups in the GMA of the graft to react with the terminal groups of the PBT resin, thereby enhancing its compatibility with PBT. The use of R-LLDPE-g-(GMA-co-St) or POE-g-(GMA-co-St) as singular modifiers did not produce optimal modification results. Conversely, the most effective modification of the PBT resin was observed when both were combined, indicating a pronounced synergistic modification effect. The optimal overall performance of the blend was noted when the R-LLDPE content in the graft copolymer was 50 wt%. This method significantly enhanced the toughness of the blend while preserving excellent thermal stability and mechanical strength, concurrently reducing the product cost. At this point, a high concentration of voids was observed in the stress-whitening area of the impact specimens. The PBT matrix displayed conspicuous shear yielding with a notably rough impact fracture surface, manifesting highly significant tough fracture characteristics. [Display omitted] • The (POE/R-LLDPE)-g-(GMA-co-St) graft copolymer is prepared, which serves as an efficient toughening agent. • The toughening of PBT with POE and R-LLDPE achieves an excellent balance between rigidity and toughness. • R-LLDPE exemplifies resource reutilization, embodying green chemistry and sustainable development principles. [ABSTRACT FROM AUTHOR]

Four different types of HDPE and LDPE were prepared, and samples (H4, L2, and L3) that exhibited similar molecular weight, melt flow index, and rheological properties as BOPE (BO) were screened. The samples were each blended, and the better compatibility of HDPE/LDPE blend system (HL1) was confirmed through the Cole-Cole plot. Thermal and thermo-mechanical properties of HL1 blend compositions were analyzed to optimize the compositions for biaxial stretching application. Especially, G′ and Tan δ were confirmed as tools to evaluate the feasibility of optimized compositions for biaxial stretching application, and the proper range of stretching temperature at which the ΔTan δ value maintained minimal energy change for biaxial stretching was determined. The modulus of the biaxially stretched samples x3 was improved by more than 10% compared to the existing sheet, and the elongation at break of all blend samples was approximately twice as good as that of BO. The better optical transparency was achieved as of biaxial stretching of blend samples, and crystal change in the stretched film compared to the sheet was clearly confirmed. From this work, it was confirmed that the G′ and Tan δ have been proved to be used as a parameter to assess the processability for biaxial stretching, and this process gave the advantage of the optimized HDPE/LDPE blend ratio with higher mechanical and optical clarity, suggesting that the blend could be applied to various packaging materials. [Display omitted] • The optimal composition of HDPE/LDPE blend was designed, and the biaxial stretching process was successfully applied. • It was suggested that the Tan δ and storage modulus, G′ from the dynamic mechanical analysis could be a newly developed analysis tool for optimizing the conditions for the biaxial stretching. • The biaxial stretching was found to be a good processing step to improve the mechanical and physical properties in HDPE/LDPE blends. [ABSTRACT FROM AUTHOR]

LDPE can be produced by different types of autoclave or tubular reactors, which can also be cascaded. An important effort is to obtain materials with autoclave-process equivalent properties from tubular technology due to economic reasons. In this way, the molecular understanding of the materials attains a key role. Five LDPE materials were characterized, covering three applications (extrusion coating, blow molding, and film blowing) as well as three reactor technologies (type I autoclave, tubular type, and type II autoclave). SEC-MALS, SEC-IR, AF4-MALS, HPLC, and 2D-LC allowed a detailed characterization of the samples' molar mass and branching structure while providing a unique opportunity for technique comparison. This allowed for an unprecedented understanding of the differences in molecular structure and the influence of application vs. reactor technology driven differences. Overall, SEC-IR-MALS was found to provide the most versatile information, making it an excellent choice for an initial characterization. Furthermore, the results indicate that the intended application (and thus property profile) influences LDPE structure much more than reactor technology. All five studied samples exhibit differences in molar mass distribution, short-chain as well as long-chain branching. Yet, the three extrusion coating samples (each derived from a different reactor type) appeared notably similar to each other with regard to each parameter. [Display omitted] • Five LDPE materials of diverse reactor origins and applications characterized. • Elucidation of variations in long-chain as well as short-chain branching of LDPE. • Branching variations of LDPE related to application profile rather than origin. • SEC-IR-MALS provides the most initial information in LDPE characterization. [ABSTRACT FROM AUTHOR]

Film blowing is a crucial plastic conversion technique for (Linear) Low Density Polyethylene ((L)LDPE), widely employed in the industry. However, understanding its complexities, which involve a delicate interplay between various parameters, such as macromolecular features, flow behavior, processing conditions, and final film performance, remains limited in the literature. Notably, the quantification of processability in film blowing has not yet been adequately addressed. Present study investigates the key parameters in this interplay, introduces a framework to quantify the processability, and establishes its connection with molecular weight (distribution) and the extensional flow behavior of (L)LDPE. Additionally, selected processing conditions are correlated with the crystalline morphology and performance of the films. The findings of this research offer a fundamental understanding of the film blowing process and serve as a valuable baseline for future endeavors involving more complicated polymer systems, such as blends and contaminated recyclates. By shedding light on the crucial parameters and their interdependencies, this work contributes to advancing the efficiency and quality of the process, facilitating the production of high-performance films. [Display omitted] [ABSTRACT FROM AUTHOR]

Various atomic force microscopy methods for the imaging and measurement of the modulus of polyethylene (PE) layers in a five-layer multilayer film are described. The film includes linear low-density polyethylene (LLDPE) products with densities ranging from 0.940 to 0.912 gm/cm3. Conventional TappingMode AFM phase imaging can reveal the layers but is sensitive to measurement conditions. PeakForce Tapping AFM using quantitative nanomechanics (QNM) mode can resolve all five layers based on at least three different signals – stiffness mapping, penetration, and energy dissipation. In particular, the difference is statistically significant for the modulus and penetration data. This is remarkable considering that the method is sensitive to density differences of only 0.004 density units. Quasistatic AFM indentation was also done using the same probe and peak load. Here we see the effect of time dependence on the mechanical properties, where the slower interaction times yield estimated moduli much closer to the long-time moduli measured in bulk tensile experiments, compared to the value obtained at much higher frequency using PeakForce Tapping AFM. Nano-thermal analysis of the same five-layer film using heated tip technology can also discriminate the layers statistically, based on softening temperature, which shows excellent correlation with bulk properties. [Display omitted] • Calibrated AFM methods measure the properties of a 5-layer LLDPE multilayer with varying densities. • TappingMode AFM provides layer contrast but is sensitive to measurement conditions. • PeakForce QNM mode can resolve all layers based on modulus, penetration, and dissipation signals. • NanoTA can distinguish all layers based on the softening transition temperature. • Layer identity is statistically significant with density resolution of at least 0.004 gm/cm3. [ABSTRACT FROM AUTHOR]

Recently, the structural symmetry of α-diimine nickel catalysts was demonstrated to have a pronounced effect on the microstructure of the resulting polyethylene. In this study, two plane symmetric α-diimine Ni(II) complexes were designed and used in ethylene polymerization. The plane-symmetric Ni(II) complexes exhibited very high activities (well above 106 g mol−1 h−1) and yielded high molecular weight (up to 1088 kg/mol) polyethylenes with tunable branching density (49–87/1000C). Compared to the corresponding centrosymmetric Ni(II) complex, the plane-symmetric Ni(II) complex yielded significantly higher branched polyethylene (77 vs 29/1000C) under the same conditions. The polyethylene products obtained by plane-symmetric Ni(II) complexes exhibited low to moderate stress (3.7–21.6 MPa) and high strain (617–4058%) at break values as well as tunable recovery values (SR = 35–79%). Compared to the centrosymmetric Ni(II) complex, the plane-symmetric Ni(II) complexes yielded polyethylene materials with higher strain and lower stress at break values, and most importantly, significantly higher SR values (68% vs. 28%) under the identical conditions. Anyway, elastomer-like polyethylene materials were obtained from plane-symmetric Ni(II) complexes while centrosymmetric Ni(II) complex yielded linear low-density polyethylene-like materials. Synopsis: The design of the catalyst plane symmetry could be used for the preparation of highly branched polyethylene elastomers. [Display omitted] • The plane-symmetric Ni(II) complexes yielded high molecular weight polyethylenes with tunable branching density. • Compared to the centrosymmetric Ni(II) complex, the plane-symmetric complex yielded significantly higher branched polyethylene. • Elastomer-like polyethylene materials were obtained from plane-symmetric Ni(II) complexes. [ABSTRACT FROM AUTHOR]

Two-dimensional (2D) layered nanomaterials, including pristine α-zirconium phosphates (ZrP), amine-intercalated organophilic α-zirconium phosphates (OZrP) and organophilic montmorillonite (OMMT), are directly incorporated into linear low density polyethylene (LLDPE) by injection molding. ZrP and OZrP achieve good dispersion in the LLDPE matrices while OMMT forms agglomerations as observed by scanning electron microscope (SEM). The differential scanning calorimetry (DSC) analysis reveals that well-dispersed ZrP and OZrP could act as a nucleating agent to increase crystallinity of LLDPE while the agglomerated OMMT decreases the crystallinity of the polymer matrix. Tensile tests show that the strength and ductility of the LLDPE/ZrP nanocomposites can be enhanced simultaneously, due to the high modulus and parallel alignment along the injection direction for ZrP in matrix. The heat resistance of LLDPE, can also be enhanced by the addition of 2D nanoplatelets, among which ZrP perform the best, showing an increase of ∼16 °C in heat distortion temperature. Image 1 • ZrP are compared with organophilic montmorillonite on reinforcing non-polar LLDPE. • ZrP exhibits a high efficiency in improving the heat resistance of non-polar LLDPE. • ZrP can significantly enhance the strength and ductility of LLDPE simultaneously. [ABSTRACT FROM AUTHOR]

Abstract Untethered octaisobutyl- polyhedral oligomeric silsesquioxane (POSS) molecularly dispersed into low-density polyethylene (LDPE) induced entanglement dilation and dynamics acceleration, reduced the melt viscosity and acted as nano-plugs thus reducing O 2 transmission. POSS nanoparticles were melt mixed with LDPE using a twin-screw extruder and adding up to 10 wt% POSS. High-resolution transmission electron microscopy (HRTEM) demonstrated excellent dispersion of POSS into LDPE, at a single POSS unit at low concentrations. The dynamics was probed by shear rheometry constructing master curves at T ref = 190 °C using the time-temperature superposition (TTS) principle. In the low concentration range (c POSS <5 wt%) the terminal (liquid-like) regime showed that POSS nanoparticles induced accelerated dynamics, decreasing the terminal relaxation time τ t. This translated into an anomalous, non-Einstein, reduction of viscosity. Increasing concentration to c∼10 wt% POSS formed clusters of ca. 10 units, the terminal relaxation time increased and the melt exhibited higher viscosity than the neat LDPE, as predicted for particulate filled suspensions. Therefore, at low concentrations the size of POSS (ca. 1.5 nm), smaller than entanglement mesh size of polyethylene (tube diameter d t = 3.28 nm), would drive chain disentanglement and be responsible for the dilution effect. At higher concentrations POSS aggregated and therefore increased the viscosity of the nanocomposite, a behavior akin to Einstein's prediction. Strikingly, the intercalation of POSS into the entangled molecular mesh reduced oxygen transmission, suggesting that POSS acted as nano-plugs by filling the voids in the entangled mesh. Graphical abstract Image 1 Highlights • Untethered POSS dispersed at a single unit in LDPE. • POSS induced chain disentanglement and viscosity reduction in LDPE. • POSS acted as nano-plug reducing O 2 transmission in LDPE. [ABSTRACT FROM AUTHOR]

Melt flow instability of LLDPE (Linear Low Density Polyethylene) and its composites with three kinds of carbon fillers with different dimensionalities, including multi-wall carbon nanotubes (MWCNTs), thermally reduced graphene (TRG) and carbon black (CB), was evaluated. A periodic oscillation in entrance pressure drop during the process of wall slip was observed. It was demonstrated that the dimensionalities of the fillers played a significant role in the rheological behaviors for LLDPE composites. The critical shear rate for the onset of the stick-slip transition increased when MWCNTs added but decreased with the addition of TRG. However, in terms of the LLDPE/CB composites, there was no obvious changes for this critical shear rate. Mechanisms for the effects of these fillers on the flow instabilities were proposed according to the molecular structure and the movement of polymer chains. [ABSTRACT FROM AUTHOR]

The influence of oleic acid modified Fe 3 O 4 (OA-Fe 3 O 4 ) nanoparticles on the morphology and foaming behavior of cocontinuous linear low density polyethylene/polystyrene (LLDPE/PS) immiscible blends (60/40 by weight) was studied. The morphology observation showed that the addition of nanofillers resulted in the increased dispersion degree of both LLDPE and PS components and even the transformation of phase structure from cocontinuous structure to sea-island structure, when enough amounts of nanoparticles were added. Meanwhile the introduction of enough amounts of OA-Fe 3 O 4 nanoparticles effectively enhanced the foaming ability of LLDPE/PS blend at semi-solid state during scCO 2 batch foaming. The mechanism analysis for the change of foaming behavior showed that the improved foaming capacity resulted from the change of the phase structure of LLDPE/PS blends and heterogeneous nucleation of OA-Fe 3 O 4 nanofillers. Sorption and desorption measurements showed that the addition of OA-Fe 3 O 4 nanoparticles in the LLDPE/PS blend increased the solubility of CO 2 , and the presence of enough amount of OA-Fe 3 O 4 decreased the desorption rate of CO 2 in the initial period of depressurization process, which are beneficial to cell nucleation and growth. Furthermore, it was found that the melt behavior and crystalline properties of LLDPE/PS blends were not the key factors to improved foaming behavior of the blends in the presence of OA-Fe 3 O 4 nanoparticles. [ABSTRACT FROM AUTHOR]

Barium titanate (BaTiO 3) filled low density polyethylene (LDPE), (LDPE) 100−x / (BaTiO 3) x (where x = 0, 2, 4, 6 and 10) nanocomposites are prepared via a solvent-free melt-mixing method. The effects of nano-sized BaTiO 3 (nBT) on the structural, optical and thermal degradation properties of LDPE are investigated to address the qualitative interfacial interaction effects due to the spatial distribution of nBT particles in the LDPE matrix. X-ray diffraction (XRD) results confirm the uniform dispersion of nBT nano-fillers in the LDPE polymer matrix. The crystallite size of LDPE increases with increasing the nBT content. Fourier transform infrared spectroscopy (FTIR) results indicate the enhancement in interfacial physical interactions between the polymer and nano-fillers with increasing nano-filler content. The band gap energy of the nanocomposites decreases with increasing nano-filler content, which suggests chemical imperfections close to the interfaces. DSC results depict higher T m values for the composites which is attributed to the heterogeneous nucleating effects of the nBT particles. Thermo-gravimetric analysis (TGA) results indicate an increase in the decomposition temperature (T D), thermal stability and good dispersibility probability of nBT with increasing nBT. The photocatalytic decomposition of MB is highest (73.52%) for the 10% nBT incorporated LDPE nanocomposite sample. These results correlate with the effect of the interfacial interactions between the nBT fillers and the LDPE polymer matrix. [Display omitted] • We have synthesized (LDPE) 1-X /(BaTiO 3) X nanocomposites using melt-mixing method. • Effects on thermal degradation properties with increasing nBT have been investigated. • Band gap narrows after the incorporation of nBT in LDPE. • Interfacial interactions and thermal stability increases, while exothermic degradation temperature (above 500 °C) decreases with increasing nBT loading. • The photocatalytic decomposition of MB is highest (73.52%) for 10% nBT incorporated LDPE nanocomposite sample. [ABSTRACT FROM AUTHOR]

In this study, we report an effective synthesis approach for fabricating low-density polyethylene (LDPE)-based multi-functional composite through hybridization with short PE chain branched boron nitride nanosheet (BNNS) to be applied as a high-performance hot-melt adhesive (HMA) type thermal interface material (TIM). To enhance the thermal and mechanical properties of BNNS/LDPE, the BNNS surface was modified with short PE chain (PE–g–BNNS) via nitrene coupling reaction to improve the interfacial bonding force between the BNNS with LDPE. As a result, PE–g–BNNS/LDPE exhibited 22% increase in through-plane and 66% increase in in-plane thermal conductivity compared to the BNNS/LDPE. Its heat radiation performance was also increased by about 11% compared to the bare LDPE. In addition, the PE–g–BNNNS/LDPE shows 66% increase in tensile strength and 350% enhancement in modulus compared to the bare LDPE, suggesting that the PE–g–BNNNS/LDPE could be used as a TIM to meet the requirements for application in high-tech electronic devices. [Display omitted] • The effective synthesis way to fabrication of high-performance BNNS/LDPE composites. • Efficient heat conduction paths were constructed by linked PE-g-BNNS with LDPE. • Enhance the performance by strengthening the coupling between BNNS and LDPE matrix. • The BNNS/LDPE composites with excellent comprehensive properties can be used as TIM. [ABSTRACT FROM AUTHOR]

Brominated polystyrene (BPS) is blended with linear low-density polyethylene (LLDPE) to improve its fire retardancy for various applications such as wire and cable covering. To improve compatibility and mechanical properties, styrene-ethylene/butylene-styrene (SEBS) copolymer was added as a compatibilizer. The influence of processing temperature and SEBS elastomer on morphology, interfacial and mechanical properties has been investigated. It was found that melt blending at 230 °C with addition of SEBS elastomer can significantly reduce the BPS particle size to less than 0.5 μm by forming a core-shell structure that enhances the interfacial strength between BPS and LLDPE phases. Addition of 8 phr SEBS elastomer can increase the Izod impact strength at −37 °C by a factor of nearly three, compared to the non-compatibilized LLDPE/BPS system. Double-notch four-point bending (DN-4PB) test reveals that crazing and shear banding are two primary toughening mechanisms for the observed increase in the low temperature impact strength. [Display omitted] • LLDPE/BPS blends were successfully compatibilized and toughened by a SEBS rubber. • A core-shell structure was formed with BPS particle size reduced to less than 0.5 μm. • Processing temperature is vital to obtain fine morphology due to viscosity match. • Izod impact strength at −37 °C is improved by about 3 times with 8 wt% SEBS added. • Crazing and shear banding are primary toughening mechanisms. [ABSTRACT FROM AUTHOR]

The localization of multi-walled carbon nanotubes (MWCNTs) in PMMA/LDPE blends was studied. Theoretical predictions suggested their preferential localization in the PMMA. Conversely, experimental work revealed that non-functionalized MWCNTs located in the LDPE, polymer first to melt. When the extrusion time is not long enough, the MWCNTs do not have the chance to further migrate to the thermodynamically most favourable phase. The evolution of a double percolation determined if the composite became semi-conductive. In that sense, two blends with PMMA to LDPE ratios of 80:20 and 20:80 containing 2 wt.% MWCNTs had electrical resistivity values in the order of 10 5 and 10 12 Ω cm, respectively. Only in the 80:20 blend was the “effective” MWCNT concentration high enough such that electrical percolation was attained. However, bulk rheological properties were controlled by the major phase. Thus, 2 wt.% MWCNTs had a notable effect on the linear viscoelasticity at low frequencies of the 20:80 blend. [ABSTRACT FROM AUTHOR]

A method for large-scale processing of low density polyethylene (LDPE) nanofibers reinforced by aligned multi-walled carbon nanotubes (MWCNTs) is achieved via nanolayer coextrusion. The morphology and nano-sized diameter of the nanofibers are observed on scanning electron microscope. The prioritized alignment and dispersion of MWCNTs along the fiber axis are determined by transmission electron microscopy, polarized Raman spectra, and high resolution optical microscopy. The dispersion of MWCNTs in nanofibers is better than that in homologous micron-fibers. In addition, MWCNTs can promote the crystallization of LDPE in varying degrees which depend on the fiber diameter and MWCNTs content. As a result of the alignment of MWCNTs, the nanofibers exhibit enhanced mechanical properties. The tensile strength of LDPE(1 wt% MWCNTs) nanofibers is more than twice of pure nanofibers (without MWCNTs). The volume resistivity of the LDPE(MWCNTs) nanofiber mats containing 9 wt% MWCNTs can be reduced to 100 Ω cm. [ABSTRACT FROM AUTHOR]

Poly (lactic acid) (PLA) has high potential to replace conventional petroleum-based plastics in a wide range of applications. However, the high brittles, thermal degradation, low melt strength and low viscosities of PLA pose challenges for its processing and performance satisfied for industrial use. Previously, we have shown that natural rubber (NR) incorporated into PLA improved the melt strength and viscosity and thus the processability of biopolyesters. Chain extension is a practical and cost-effective method of improving PLA processability by enhancing the molecular weight and re-bonding degraded chains. We hypothesized that addition of epoxy-based chain extenders will work synergistically with natural rubber to improve the elongational viscosity and strain hardening of PLA. The thermal transition, thermal degradation, mechanical and moisture barrier properties were studied to provide a comprehensive view of the chain-extended and NR-modified PLA. The results shows that chain extender with higher functionality (Joncryl 4368) had a more significant effect on chain extending, branching and restoring of PLA. Although the chain extender or the NR alone reduced both the dynamic and steady shear viscosities and minimally affected the elongational viscosity of PLA, they together resulted in shear-thickening and strain-hardening of PLA, suggesting a synergistic effect of the chain extender and NR on improving PLA rheological performance. The improved elongational viscosity of PLA was comparable to film grade low density polyethylene (LDPE). Additionally, NR addition significantly reduced the water vapor permeability of PLA. The PLA with improved melt viscosity and moisture barrier are promising for film and flexible packaging applications. [Display omitted] • Epoxide and natural rubber work synergistically on improving PLA rheology and processability. • The improved elongational viscosity of PLA is comparable to low density polyethylene (LDPE). • Rubber addition significantly reduced the water vapor permeability of PLA. • PLA with improved processability and barrier is promising for flexible packaging application. [ABSTRACT FROM AUTHOR]

The correlation between the modulus of the interlamellar amorphous phase and the microstructure of the crystalline component was studied. The experimental method involving deformation of the amorphous layers only developed by us was used. Three polyethylenes with different architecture of macromolecules and thermal history were analyzed. In the case of HDPE and low density polyethylene (LDPE), a practically linear increase of the elastic modulus of the confined amorphous phase with the increase of the crystal thickness (in the range of ≈4–20 nm) was observed and explained by activation of α relaxation process in crystalline lamellae. For thin crystals the degree of activation of the α relaxation was intense and the influence of crystalline component on the modulus of amorphous regions was the lowest. For materials with thick crystals the degree of activation of the α relaxation was lower and the "confining" influence of crystalline component on the amorphous phase was the highest. In ethylene-octane copolymer (EOC) materials with the thinnest crystals (≈2–3 nm) the modulus of the confined amorphous phase was close to the modulus of the bulk amorphous phase-in those materials the α relaxation process was not observed at all. The modulus of the amorphous phase of isothermally crystallized HDPE (≈70 MPa) was over twenty times higher than the modulus of the bulk amorphous phase (≈3 MPa). [Display omitted] • Three polyethylenes (PEs) with different thickness of crystals (l c) were analyzed. • The modulus of the interlamellar amorphous phase (E a) of PEs were determined. • Linear increase of E a with the increase of l c was observed. • E a.→ l c was correlated with the α relaxation process activated in crystalline lamellae. [ABSTRACT FROM AUTHOR]

Peroxide-initiated low-density polyethylene (PLPE) has been extensively used as insulating materials for high-voltage cables, while the lack of comprehensive knowledge on crosslinking process of PLPE seriously limits the development of cable insulation. Here, the crosslinking process and mechanism of PLPE are fully revealed by combining kinetic and chemorheological analysis for the first time. Rheological parameters during crosslinking process of PLPE are obtained by dynamic rheology experiments at different frequencies and temperatures. Crosslinking kinetics of PLPE is explored by rheological conversion method and diffusion-controlled Kamal-Sourour model. Meanwhile, chemorheological behaviors of PLPE are discussed based on percolation theory and Arrhenius law. The results indicate that the crosslinking reaction of PLPE involves complex n-order and autocatalytic reactions. Importantly, the autocatalytic reaction and the gelation formation significantly enhance the reaction rate. Furthermore, physical diffusion of macromolecular chains obviously reduces the reaction rate and prolongs the termination reaction. Based on that, the mutual influences and relationships between the kinetic and chemorheological behaviors are established by combining the apparent activation energy. It is suggested that PLPE crosslinking process is controlled by alternant synergistic action of chemical reaction and physical diffusion. This work can provide a critical theoretical basis for the comprehension and optimization of PLPE crosslinking process. [Display omitted] • PLPE crosslinking reaction involves both n-order and autocatalytic reaction. • Mutual relationships between kinetics and chemorheology behaviors are established. • Crosslinking process is controlled by chemical reaction and physical diffusion. [ABSTRACT FROM AUTHOR]

We present a computational study of the development of structural properties for recycled low-density polyethylene (LDPE). First, we apply the population balance method together with the method of moments to study the mutual influences of scission and crosslinking reactions. Then, we study the combined effects of extruder residence time and oxygen concentration as the initiator of thermo-mechanical degradation in the recycling process of LDPE in a twin-screw extruder. Further, we extend the models to study the influence of mechanical scission. We explore various case study scenarios to incorporate the effect of extruder residence time and mechanical shear. It is concluded that the competition between random scission and crosslinking, as well as the presence of oxygen, play important roles in the degradation of LDPE during recycling. Random scission is a key factor in terms of altering molecular weight distribution (MWD) during a recycling extrusion process. The various explored scenarios with mechanical scission demonstrate the sensitivity of molecular structure to the combination of competing mechanisms during recycling. a)Dead chains distribution and b) Average number of branch points per chain length from the deterministic modeling with topological scission, termination by combination, crosslinking and mechanical scission for recycled LDPE. [Display omitted] • Simulation methods enable computation of polymer topology changes during extrusion. • Mechanical scission affects structure of recycled LDPE in interaction with other effects. • Competing mechanisms during recycling show that scission is key for MWD changes. [ABSTRACT FROM AUTHOR]

In this work, novel rectangle and circular orifice (zero-length) dies have been utilized for temperature-strain rate dependent planar and uniaxial extensional viscosity measurements for the LDPE polymer melt by using standard twin bore capillary rheometer and Cogswell model and the capability of five different constitutive equations (novel generalized Newtonian model, original Yao model, extended Yao model, modified White-Metzner model, modified Leonov model) to describe the measured experimental data has been tested. It has been shown that chain branching causes the strain hardening occurrence in both uniaxial and planar extensional viscosities and its maximum is shifted to the higher strain rates if the temperature is increased. The level of uniaxial extensional strain hardening for the branched LDPE sample has been found to be higher in comparison with the planar extensional viscosity within wide range of temperatures. [ABSTRACT FROM AUTHOR]

An advanced analytic method, based mainly on thermorheological analysis of standard frequency sweeps at several temperatures, is introduced which can determine a host of rheological indicators for long-chain branched polyethylenes and other materials with an Arrhenius-type temperature dependence. The method can be used to classify and categorize unknown samples to material types (tubular and autoclave low density polyethylene, long-chain branched metallocene polyethylene). For long-chain branched metallocene polyethylenes, it is, furthermore, possible to determine molar mass and branching degree using established relations with rheological behavior. It is, therefore, possible to gain a rather comprehensive picture of the molecular structure of long-chain branched polyethylenes using only a relatively simple set of rheological experiments. An automated analysis routine facilitates the evaluation. [ABSTRACT FROM AUTHOR]

The smart energy absorption and storage properties make the phase change materials the ideal candidate for solar thermal conversion and afterheat utilization. Applying the vane extruder (VE) coupled with a single-layer blown film die, a fast and efficient one-step method is proposed for the successive and mass production of LDPE/PEO/CNTs (PPCs) nanocomposite films. Benefiting from the volumetric elongational flow field provided by the VE, the CNTs are uniformly dispersed in the matrix and a co-continuous network is formed, thereby the thermal conductivity and tensile strength of the PPCs film are effectively improved. The melting enthalpy of PPC 0.02 film is 110 J g−1 and tensile strength is 3.308 MPa. Furthermore, the PPCs films maintain stable phase change temperature and robust chemical properties after 150 thermal cycles. The temperature of the simulated greenhouse can be controlled within the range that is conducive to crop growth when the PPCs film is applied to its roof. This can be ascribed to the sufficient light-to-thermal conversion capability and thermal conductivity of the PPCs film. The PPCs film with sufficient shape stability and leakage resistance can be an excellent candidate for harvesting and recycling solar and heat energy sources. A fast and efficient one-step method is proposed for the successive and mass production of LDPE/PEO/CNTs (PPCs) nanocomposite film though the vane extruder coupled with a single-layer blown film dies. The prepared PPCs films have excellent encapsulation property mechanical, strength, light-to-thermal and thermal management property. [Display omitted] • An efficient method is proposed for the preparation of LDPE/PEO/CNTs films. • The property of the film is improved under the volumetric extensional rheology. • The prepared film exhibits robust chemical stability after 150 thermal cycles. [ABSTRACT FROM AUTHOR]

Deoxyribonucleic acid (DNA) was investigated as a flame retardant (FR) additive for melt-compounded formulations with low-density polyethylene (LDPE) and compared to LDPE compounded with melamine polyphosphate (MPP), one of the industry standard intumescent FR additives for plastics. DNA showed a much greater compatibility with the LDPE matrix than MPP. At high loading levels, DNA showed minimal increases in compounding torque, while MPP increased torque by over 20%. Qualitative evaluation using SEM and EDS showed that DNA/LDPE blends had significantly improved cross-sectional morphology, with fewer microaggregates and improved particle dispersion than MPP/LDPE. Horizontal burn testing showed that DNA markedly reduced flame burn distances in LDPE above loading levels of 5% w/w. Biochemical characterization of heat-treated DNA revealed that DNA undergoes denaturation, fragmentation, and oxidation during compounding, but these processes did not appear to have an effect on its FR properties. This study expands the field of DNA-based FR beyond specialty substrates, and establishes DNA as a viable green FR additive for commodity polymer applications. [ABSTRACT FROM AUTHOR]

A new experimental approach based on essential work of fracture (EWF) method and an in-situ digital image correlation strain mapping analysis has been developed to quantify different aspects of fracture energy on model metallocene linear low-density polyethylene (m-LLDPE) blown films. Three distinctive fracture process zones have been identified from the photoelastic observation of the model m-LLDPE blown films. These three zones include the essential work ( W e ) zone due to necking and crack propagation, the non-essential plastic deformation zone ( W p ), and a newly proposed recoverable viscoelastic deformation zone ( W v ), which is found to be nontrivial. Furthermore, in contrast to the assumption involved in the EWF theory, W e is found to be proportional to the volume of the materials involved in the inner fracture process zone. The current approach allows for exact physical interpretation of the EWF parameters and their correlation to material characteristics. Usefulness of the present work for development of stronger polymeric blown films is discussed. [ABSTRACT FROM AUTHOR]

The primary and secondary crystallization kinetics of a homogeneous linear low-density polyethylene were characterized as function of cooling rate, pressure and flow strength. Our approach to describe primary crystallization is based on nucleation and growth of spherulites, quantified well below the melting temperature using small-angle light scattering. The description of the two-step secondary process is coupled to primary crystallization using a convolution integral, for which the parameters were determined from (fast-) differential scanning calorimetry. Extended-dilatometry was used to investigate the effect of different thermomechanical histories. Parameters were determined for an existing model that couples molecular stretch to both nucleation rate and fibrillar growth rate. Excellent agreement is shown between calculated and experimentally obtained crystallization kinetics in conditions representative for those found in real-life processing conditions. This opens the possibility to calculate in detail the evolution of and the final crystallinity structure in products such as blown film or extruded tape. [ABSTRACT FROM AUTHOR]

Silica nanoparticles (SiO 2 NPs) were prepared and functionalized with polyethylene (PE@SiO 2 NPs) using the surface-initiated polyhomologation (SI-polyhomologation) technique. Polyolefin nanocomposites were fabricated later by melt mixing of different ratios of the as-prepared SiO 2 NPs and PE@SiO 2 NPs with linear low-density polyethylene (LLDPE) and low-density polyethylene (LDPE) matrices. Firstly, SiO 2 NPs were modified with different alkoxysilane ligands, dichloro(divinyl)silane (DCDVS), allyl trimethoxysilane (ATMS), and vinyl triethoxylsilane (VTES). Subsequently, thexylborane, an initiator for SI-polyhomologation, was immobilized to the modified surface of SiO 2 NPs through hydroboration reactions. Polyhomologation was then allowed to proceed by adding monomer solution to form polyethylene brushes covalently bonded to the surface of the NPs. Physiochemical characterizations had confirmed the morphology, chemical structure, and thermal stability for each step of modification reactions. LLDPE and LDPE nanocomposites were prepared by extrusion with SiO 2 NPs and PE@SiO 2 NPs as nanofillers. Finally, tensile tests and morphological SEM-based analyses are presented to discuss the influence of the grafted PE on both the dispersion of the fillers and the mechanical properties of the filler/matrix interphase. [Display omitted] • Polyethylene grafted nanosilica. • SI-Polyhomologation. • Polyolefin/silica nanocomposites. [ABSTRACT FROM AUTHOR]

In this research work, multilayer soft film/foam systems based on low-density polyethylene (LDPE) have been developed. In order to improve the layer stability during processing, a viscosity contrast between film and foam layer polymers is maintained. Three different LDPE grades having different melt flow indices were used and film/foam systems with up to 32 layers were produced. High-viscosity film layer and low-viscosity foam layer in each film/foam system contributed to good layer integrity even with high foam content. Measurements of cell density and cell size distribution indicated that high viscosity film layer and increasing layer number have significant confinement effect that enhanced the cell nucleation and suppressed the cell coalescence and thus contributed to single cell arrays in foam layers. Constrained cell growth was observed in 16 and 32 layers film/foam systems. Confinement effect from the high viscosity film layer was also observed at higher foam content. In addition, uniform layer integrity resulted from high viscosity contrast between film and foam layers contributed to higher deformability. Moreover, increasing layer number also improved the tensile modulus and strength of each film/foam system. [ABSTRACT FROM AUTHOR]

This study shows an additive assisted one-step melt mixing approach to produce composites of linear low density polyethylene (LLDPE) with carbon nanotubes (CNTs) which are nearly free of CNT agglomerates. Thereby, the influence of an nonionic additive namely polyoxyethylene cetyl ether as a dispersion additive during the CNT melt mixing process was investigated. It was analysed how the number of the polyoxyethylene repeating units or the exchange of the functional groups affect the dispersion mechanisms of multiwalled carbon nanotubes (MWCNT) namely Nanocyl™ NC7000 in LLDPE. Thereby the supposed CNT dispersion mechanism is explained as schematic overview. In summary, the CNT macrodispersion is improved if the number of polyoxyethylene repeating units increases. Through the addition of polyoxyethylene (20) cetyl ether the percolation threshold can be reduced to about 1 wt.% with a simultaneous homogeneous dispersion of CNTs. Additionally at an MWCNT loading of 2 wt.% and 8 wt.% of polyoxyethylene (20) cetyl ethers the strain at break increases by 113% in comparison to corresponding composite without the additive while modulus and stress at break generally decrease with additive addition. [ABSTRACT FROM AUTHOR]

Layer multiplying coextrusion was employed to produce films consisting of alternating layers of unfilled and particulate filled polymers, i.e., low density polyethylene (LDPE) and maleic anhydride grafted linear low density polyethylene (LLDPE-g-MA)/organoclay nanocomposites. Layer multiplying coextrusion was employed to produce gas barrier films consisting of alternating layers of unfilled and particulate filled polymers, i.e., low density polyethylene (LDPE) and maleic anhydride grafted linear low density polyethylene (LLDPE-g-MA)/organoclay nanocomposite. To further enhance gas barrier performance, the clay concentration within the nanocomposite layers was increased several fold through annealing of the multilayer film in the melt state. Residing in the melt state activated the interdiffusion between the polymers and due to a significant difference in the molecular mobility between the LDPE and LLDPE-g-MA chains led to a moving boundary effect which contracted the (LLDPE-g-MA)-rich nanocomposite layers and expanded the LDPE-rich layers. Analysis of the clay morphology within the nanocomposite layers demonstrated an increase in the clay particle lengths and aspect ratios, which was attributed to the growth of “skewed” aggregates during layer contraction and particle concentration. The melt induced clay concentration and increased clay particle dimensions caused a significant decrease in oxygen permeability of the nanocomposite layers and reduced the overall permeability of the multilayered films. Morphology and transport behavior of the multilayered films were compared to a series of LLDPE-g-MA/clay bulk nanocomposites with varying clay content prepared by melt compounding in a twin screw extruder. Nielsen and Cussler models were used to describe the gas barrier data of the nanocomposite films. Although both models can be fit well to the experimental data, the Cussler model showed a better agreement with the morphological observations. [ABSTRACT FROM AUTHOR]

This paper proposes a set of models to calculate contraction factor, which to maximum extent accounts for the kinetics of radical polymerization with transfer to polymer and recombination termination. The models are alternatives to the Zimm and Stockmayer's (1949) analytical expression of contraction factor for molecules with terminal branching. The results, being representative for polymers like as low-density Polyethylene (ldPE), show significantly stronger contraction than predicted by the model of Zimm and Stockmayer. In the case of termination by disproportionation only, molecular sizes turn out to be smaller by a factor of almost two. In presence of recombination termination molecules are less compact. It is shown that the interpretation of contraction factors as measured by the Size Exclusion – Multi-Angle Light Scattering to find the branchedness of ldPE, with the new model would lead to a considerably lower estimate of branching than by using Zimm and Stockmayer's model. [ABSTRACT FROM AUTHOR]

The blend of linear low density polyethylene (LLDPE) and ethylene vinyl alcohol (EVOH) with weight fraction of 50–50 is extruded through a series of multipliers to fabricate thin films. Different numbers of multipliers are utilized to tailor the morphology of the extruded blend films. We discover that as the number of multipliers increases, the blend film morphology evolves dramatically. The elongated and layer-like structure is gradually replaced by well-dispersed nano-blend morphology when the number of multipliers reaches eight. The domain size of each component decreases due to the effect of multiplication process. This is because during the multiplication process, multipliers behave similar to static mixers that physically break the elongated and layer-like structure of LLDPE and EVOH into tiny domains. Along with the morphological evolution, the physical properties of the extruded blend films change greatly. Atomic force microscopy (AFM) and wide angle X-ray scattering (WAXS) are utilized to investigate the morphology and crystalline structure of the blend films. Oxygen gas permeability and water vapor transport rate (WVTR) are measured by MOCON units. The transmission rate and mechanical properties are studied by the UV–vis and a mechanical tensile stretcher (MTS) respectively. We report that both oxygen permeability and WVTR increase as the number of multipliers increases. The transparency is improved as more multipliers are used. The last but not the least, tensile mechanical behaviors gradually become isotropic at different deformation directions as the morphology changes. [ABSTRACT FROM AUTHOR]

Blends of linear low density polyethylene (LLDPE) and ethylene vinyl alcohol (EVOH) with different weight fractions are extruded to fabricate thin films. The extruded blend film morphology is investigated by atomic force microscopy (AFM). The extruded blend films have shown extended morphology along the extrusion direction (ED) and dispersed morphology along the transverse direction (TD). We report that due to this morphology, a two-dimensional (2-D) confined crystallization occurs. The EVOH has successfully confined the LLDPE from both film normal direction (ND) and transverse direction (TD) in this study. The confinement from ND results in an on-edge orientation of LLDPE, while the confinement from TD forces the on-edge oriented LLDPE crystals to further elongate and extend along the extrusion direction (ED). This specific crystal orientation is different from one-dimensional (1-D) confined crystallization observed in multilayered films. Both wide angle X-ray scattering (WAXS) and small angle X-ray scattering (SAXS) are utilized to investigate the crystal orientations of LLDPE in the extruded blend films. Moreover, due to the morphology, the extruded blend films have shown high oxygen barrier properties, which make this material valuable in packaging applications. [ABSTRACT FROM AUTHOR]

Abstract: The multilayered propylene–ethylene copolymer (CPP)/low density polyethylene (LDPE) composite sheets were prepared by the microlayered coextrusion system. The essential work of fracture (EWF) method was firstly used to quantitatively evaluate the fracture behavior of layered materials. The experimental results indicated that the two-dimensional layered interfaces in the multilayered materials could play an important role in the fracture behavior. The specific essential work of fracture, w e, increased with the layers due to interfacial delamination. Additionally, the different testing speeds had a dual effect on the increscent trend of the specific essential work of fracture, w e, with increasing layers. [Copyright &y& Elsevier]

Abstract: The in-line development of crystalline morphology and orientation during melt extrusion of low density polyethylene (LDPE) tape at nil and low haul-off speeds has been investigated using Small-Angle X-Ray Scattering (SAXS). The processing parameters, namely haul-off speed and distance down the tape-line have been varied and the resulting crystalline morphology is described from detailed analysis of the SAXS data. Increasing haul-off speed increased orientation in the polymer tape and the resulting morphology could be described in terms of regular lamellar stacking perpendicular to the elongation direction. In contrast, under nil haul-off conditions the tape still showed some orientation down the tape-line, but a shish-kebab structure prevails. The final lamellae thickness ( ∼50 Å) and bulk crystallinity (∼20%), were low at, for all processing conditions investigated, which is attributed to the significant short-chain branching in the polymer acting as point defects limiting lamellae crystal growth. [Copyright &y& Elsevier]

The application of polyethylene in artificial turf promotes research on the processing and properties of uniaxial extension modified polyethylene materials. The effects of comonomer (octene/butene) structure on the properties of pre-stretched linear low density polyethylene (LLDPE)/polyolefin elastomer (POE) blends are investigated. The melt tensile stress and melt stretch ratio of LLDPE ethylene‒octene copolymer (EOC)/POE reach 4.0 × 105 Pa and 12.8, respectively. At the pre-stretching ratio λ = 5, the tensile strength of EOC/POE λ5 reaches 62.5 MPa, the critical length is 5.7 mm, and the strain hardening degree increases. Differential scanning calorimetry, Raman spectroscopy and X-ray diffraction show the crystallinity of EOC/POE λ5 is higher than that of LLDPE ethylene‒butene copolymer (EBC)/POE λ5. Large short-chain branch length EOC is demonstrated to rebuild the "physical crosslinking point" after pre-stretched, thereby enhancing the interaction between molecular chains in EOC/POE λ5. This research provides a new clue for the development of artificial turf materials. [Display omitted] • Pre-stretched ethylene‒octene copolymer/polyolefin elastomer blends are researched. • Pre-stretching improves mechanical properties of blends. • "Physical crosslinking points" strengthens inter-chain-segmental forces. [ABSTRACT FROM AUTHOR]

We present a comprehensive model to computationally study molecular structure development in the recycling extrusion process of low-density polyethylene (LDPE) and provide initial results versus reported experiments as guidance. Molecular weight distribution (MWD) and branching distribution (BD) are modeled by applying a combination of population balance modeling, the method of moments and branching pseudo distributions. Special cares have been taken to incorporate the effects of scission and crosslinking reactions. Further, effective strategies have been provided to mitigate the computational complexity of solving balance equations. The models have been applied to the case of increasing residence time in a recycling extruder. The simulated MWD of the recycled LDPE exhibits a shift towards lower chain lengths for residence times up to 400 s , while for higher residence times the high MW tail forms. The evolution of the simulated BD during recycling reveals important modifications versus the original virgin LDPE with implications for derived properties. [Display omitted] • Scission and crosslinking reactions are thermally initiated in recycling processes. • Scission and crosslinking reactions degrade polymers in recycling. • Population balance modeling reveals the structural changes in recycled polymers. • Extruder residence time plays an important role in degradation of recycled polymers. [ABSTRACT FROM AUTHOR]

Biotreatment is an environmentally friendly process for pollution control. A novel biotreatment process was investigated for the degradation of plastic wastes. The biodegradation of low-density polyethylene (LDPE) films using a bacterial consortium capable of peroxidase production in the presence of H 2 O 2 was investigated for a 12-month period. Effective biodegradation was observed using the selected bacterial consortia; a 19.8% weight loss was detected during 12 months of biotreatment of the LDPE films. The daily addition of H 2 O 2 to the bioreactor stimulated the microbial activity resulted in improving the weight loss to 22.5% due to the in-situ production of peroxidase. The number average molecular weight (Mn) decreased by 20.1 and 49.5% when the polyethylene sample was biotreated for 12 months in the absence and presence of H 2 O 2 , respectively. The depolymerization of the LDPE films during the biotreatment using the selected bacterial consortia was confirmed by increasing the value of polydispersity index. The morphological and structural analyses confirmed the efficient decomposition of the LDPE films using the selected bacterial species, showing that the selected bacteria could use the LDPE films and/or their degradation intermediates as carbon and energy sources. Overall, using a peroxidase-generating bacterial mixed culture is a promising biotechnique for the efficient biodegradation of the polyethylene wastes. [Display omitted] • Biodegradation of the LDPE films using a bacterial mixed culture was examined. • Efficient biodegradation of the plastic films was recorded within 12 months. • Adding H 2 O 2 to the bioreactor stimulated the LDPE biodegradation due to the formation of peroxidase. • H 2 O 2 -stimulated biodegradation is a promising method for treating the polyethylene wastes. [ABSTRACT FROM AUTHOR]

Abstract: Linear low density polyethylene (LLDPE)/multi-walled carbon nanotube (MWCNT) composites were prepared by melt compounding, following two different compatibilization strategies that involved non-covalent interactions between the matrix and the filler. The first approach involved grafting pyridine aromatic moieties on the maleated polyolefin backbone, which are able to interact by π–π stacking with the surface of the nanotubes. The second method implemented non-covalent/non-specific surface functionalization of the MWCNTs with a hyperbranched polyethylene (HBPE). The enhanced interfacial interactions established in the composites containing LLDPE functionalized with pyridine grafts improved the dispersion of the nanotubes within the polymer matrix. Dispersion was also favoured by higher matrix viscosity. Composites containing finely dispersed MWCNTs exhibited an increase in the rheological and electrical percolation thresholds, and a significant improvement in mechanical properties. On the contrary the composites based on the low viscosity matrix contained large amounts of aggregates, which promoted lower percolation thresholds. Manipulation of matrix viscosity and compatibilization resulted in composites with good mechanical properties, and low percolation thresholds. [Copyright &y& Elsevier]

Abstract: Strategies employing 4-acryloyloxy-2,2,6,6-tetramethylpiperidine-N-oxyl (AOTEMPO) to control the onset, rate and yield of polyolefin cross-linking are demonstrated and discussed in terms of underlying reaction mechanisms. Rheological studies of a wide range of dicumyl peroxide (DCP) + AOTEMPO formulations confirm that linear low density polyethylene (LLDPE) cross-linking can be delayed precisely and consistently without adversely affecting cure yields. The importance of peroxide thermolysis rates and alkoxy radical fragmentation to reaction outcomes is established by comparison of DCP with alternate initiators, and the compatibility of AOTEMPO cure chemistry with diacrylate coagents is investigated. [Copyright &y& Elsevier]

Abstract: An alternative method for characterizing longer-than-B6 short chain branches (SCB) in polyethylene (PE) by solution 13C NMR technique was introduced in this communication. Instead of relying on chemical shift values of the methine peak, this new method was based on the chemical shift difference (Δδ) between CH(B n ) and CH(B4) where the subscript “n” denotes the number of branch carbons. In order to take advantage of the reference CH(B4) peak using this method, an ethylene/1-hexene copolymer may have to be mixed in with the unknown sample material. Several examples were given in this manuscript demonstrating this method to be more reliable in distinguishing branch lengths up to B20 than the traditional δ-value based method. Possible application to distinguishing PE long chain branching (LCB) from B6+ SCBs in HDPE and LDPE was also examined. [Copyright &y& Elsevier]

Abstract: An additive-assisted one-step melt mixing approach was developed to produce nanocomposites based on linear low density polyethylene (LLDPE) with multiwalled carbon nanotube (MWCNT). The polymer granules, nanotube powder (2 wt% Nanocyl™ NC7000) and 1–10 wt% of the non-ionic additives poly(ethylene glycol) (PEG) or poly(ethylene oxide) (PEO) with molar masses between 100 g/mol and 100,000 g/mol were simply fed together in the hopper of a small-scale DSM Xplore 15 twin-screw microcompounder. The produced MWCNT/LLDPE composites showed excellent MWCNT dispersion and highly improved electrical properties as compared to samples without the additive, whereas the effects depend on the amount and molar mass of the additive. When 7 wt% PEG (2000 g/mol) were used, a reduction of the electrical percolation threshold from 2.5 wt% to 1.5 wt% was achieved. [Copyright &y& Elsevier]

Abstract: Dicumy peroxide (DCP) modification of low density polyethylene (LDPE) below gel point (GP) produces modified LDPE (mLDPE) with wide molecular weight distributions while the random crosslinking beyond GP yields crosslinked LDPE (XLPE). Molecular weight distributions of mLDPE below GP and the sol-fractions of XLPE above GP were investigated. The sol-fractions in XLPE were extracted to prepare XLPE gels of different crosslinking densities. Both XLPE and the gels were subjected to shear action for studying dynamic rheology and relaxation modulus in the linearity region for revealing the role of entanglements and dangling chains to viscoelasticity of the randomly crosslinked network. The results revealed that the sol-fractions with molecular weight much higher than entanglement molecular weight contributed to equilibrium modulus in addition to the gel network, which lowered the DCP dosage for appearance of critical gel behavior of XLPE in comparison with the XLPE gel. However, rheological method yielded critical DCP dosages for appearance of apparent gel behaviors far beyond the chemical GP from the extraction experiment. The sol-fraction residing in the network gave rise to additional contribution to relaxation modulus of XLPE, shortening network relaxation time and improving equilibrium modulus. [Copyright &y& Elsevier]

Abstract: Film embrittlement criteria were determined for photo-oxidative degradation of linear low density polyethylene (LLDPE) films by using a range of characterisation techniques: tensile, high-temperature GPC, MAS-NMR, FTIR-ATR, WAXS and SAXS. The key embrittlement criteria was the loss of 95% elongation at break and the reduction in interlamellar distance, reduced down to approximately 30–50 Å, as a result of recrystallisation of mobile short chain fragments produced from chain scission reaction. Interlamellar thinning correlated well with the changes in double yield points seen in the tensile data, where the absence of the second yield point signified that the tie molecules at the lamellar interface underwent chain scission and could no longer transfer the tensile stress to reach c-axis slip of the lamellar crystals. This was also supported by a reduction in amorphous–lamellar interfacial width with ageing time, extracted from SAXS data using the linear correlation function. [Copyright &y& Elsevier]

Abstract: Multi walled carbon nanotubes have been incorporated into a linear low density polyethylene matrix through high energy ball milling technique at room temperature, without any chemical modification or physical treatment of the nanotubes. Highly oriented samples, with different draw ratios, were obtained by drawing at 80 °C the composite films. SEM and FTIR results on the drawn PE films demonstrate that the molecular chains in both crystalline and amorphous phases are well oriented along the drawing direction. The effect of different weight percent loadings of nanotubes and draw ratio on the morphology, thermal, mechanical and electrical properties of the composite fibers have been investigated. [Copyright &y& Elsevier]

Abstract: Linear low density polyethylene (LLDPE) can suffer from melt extrusion defects including sharkskin, cyclic melt fracture, and gross melt fracture during processing. Arborescent polymers are dendritic macromolecules with characteristics, such as a compact structure and a rigid spherical topology, making them potentially useful as polymer processing additives (PPA) to alleviate melt extrusion defects. Arborescent polystyrene-graft-polyisoprene copolymer samples were synthesized from polystyrene substrates of linear and branched architectures functionalized with acetyl groups, and coupled with polyisoprene macroanions. A linear polyisoprene sample was also investigated for comparison. The polymers were hydrosilylated with (tridecafluoro-1,1,2,2-tetrahydrooctyl)dimethylsilane on 17–52% of the isoprene units and blended with LLDPE at 0.1 and 0.5% w/w to evaluate their performance as PPA by extrusion at different shear rates. All the samples led to some degree of improvement in the extrusion of LLDPE, albeit the performance of the branched additives was inferior to a commercial fluoroelastomer PPA. The lower molecular weight and more compact (G0 or comb-branched) PPA generally performed better than those with a high molecular weight. Several PPA samples induced the early onset of cyclic melt fracture but glossy, defect-free surfaces were obtained at higher shear rates. This suggests that a minimum shear rate is required for these additives to coat the extrusion die under the experimental conditions used. [Copyright &y& Elsevier]

Abstract: This paper presents correlations between polyethylenes of different compositions and branching architectures and their viscoelastic behavior in dependence on the temperature and demonstrates how effectively rheological experiments can be used for analytical purposes. Long-chain branched polyethylenes are known to be thermorheologically complex. But the thermorheological complexity of long-chain branched linear low-density metallocene polyethylenes (LCB-mLLDPE) differs from that of low-density polyethylenes (LDPE) in the way that the activation energy of LDPE becomes constant by a temperature-dependent modification of the moduli whereas a constant activation energy cannot be obtained for LCB-mLLDPE. These findings are explained by the assumption that the LCB-mLLDPE investigated consist of at least two species with distinctly different activation energies. This interpretation is supported by the thermorheological analysis of a blend of known parts of an LDPE and a linear low-density polyethylene (LLDPE). A thermorheological complexity was found similar to that of the LCB-mLLDPE which reflects the different activation energies of the two components. Results of that kind make it possible to get information on the composition of LCB-mLLDPE not available from common analytical methods. [Copyright &y& Elsevier]

Abstract: This paper is concerned with the fabrication of voided polyethylene microstructures by heat melding of plastic microcapillary films (MCFs) to form microcapillary monoliths (MCMs), which are consolidated layers of MCFs forming in two-dimensional arrays of microcapillaries. MCMs were manufactured by heat melding multiple layers of low-voidage MCFs or high-voidage MCFs. The optimal conditions for interface adhesion of the MCFs to create MCMs without compromising capillary integrity were investigated. The MCFs were processed from linear low-density polyethylene (LLDPE) and the melt rheology of the polymer was studied to provide rheological parameters that could be used both to gain an understanding of the character of the polymer and for modeling of the MCM forming process. In particular, the temperature dependent nature of the rheology was investigated at the transition from viscous-dominated behavior to elastic-dominated behavior. Modeling of the melding process provided some additional information and confirmed issues in relation to the thermal bonding temperatures and mechanisms. [Copyright &y& Elsevier]

Abstract: A time-resolved Fourier Transform Infrared-Attenuated Total Reflectance Spectroscopy (FTIR-ATR) technique was set up and used to study the diffusion of eugenol through Linear Low Density Polyethylene (LLDPE) at 16, 23 and 40°C. The 1514cm−1 peak for eugenol (aromatic –C stretching) was monitored over time and used to determine the diffusion coefficient (D). The Fickian model was found to fit well to the experimental data and the D value of eugenol through LLDPE was found to be between 1.05±0.01 and 13.23±0.18×10−10 cm2/s. The FTIR-ATR results were compared with one and two side diffusion process using a permeation cell and quantified by High Performance Liquid Chromatography (HPLC) technique. Eugenol sorbed in LLDPE samples at different times, was extracted in methanol and the concentration determined by HPLC. The diffusion coefficient by both two-sided and one-sided HPLC technique was found to be approximately three times higher than the FTIR-ATR values although they were in the same order of magnitude of 10−10 cm2/s. The difference between the FTIR-ATR and HPLC results was mainly attributed to difference between the two measuring techniques. [Copyright &y& Elsevier]

Abstract: A series of polyethylene (PE) blends consisting of a linear high density polyethylene (HDPE) and a linear low density polyethylene (LLDPE) with an octane-chain branch density of 120/1000 carbon was prepared at different concentrations. The two components of this set of blends possessed isorefractive indices, thus, making it difficult to detect their liquid–liquid phase separation via scattering techniques. Above the experimentally observed melting temperature of HDPE, T m =133°C, this series of blends can be considered to be in the liquid state. The LLDPE crystallization temperature was below 50°C; therefore, above 80°C and below the melting temperature of HDPE, a series of crystalline–amorphous PE blends could be created. A specifically designed two-step isothermal experimental procedure was utilized to monitor the liquid–liquid phase separation of this set of blends. The first step was to quench the system from temperatures of known miscibility and isothermally anneal them at a temperature higher than the equilibrium melting temperature of the HDPE for the purpose of allowing the phase morphology to develop from liquid–liquid phase separation. The second step was to quench the system to a temperature at which the HDPE could rapidly crystallize. The time for developing 50% of the total crystallinity (t 1/2) was used to monitor the crystallization kinetics. Because phase separation results in HDPE-rich domains where the crystallization rates are increased, this technique provided an experimental measure to identify the binodal curve of the liquid–liquid phase separation for the system indicated by faster t 1/2. The annealing temperature in the first step that exhibits an onset of the decrease in t 1/2 is the temperature of the binodal point for that blend composition. In addition, the HDPE-rich domains crystallized to form spherulites which decorate the phase-separated morphology. Therefore, the crystal dispersion indicates whether the phase separation followed a nucleation-and-growth process or a spinodal decomposition process. These crystal-decorated morphologies enabled the spinodal curve to be experimentally determined for the first time in this set of blends. [Copyright &y& Elsevier]