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Silicone foam (SF) is a porous silicone rubber with a lower density, higher elasticity, and good thermal stability. In this work, we selected aluminum spheres and carbon fiber (CF) as thermally conductive fillers to prepare hybrid SF. After optimization, we found that Al and CF hybrid SF (Al-CF-SF) has a higher thermal conductivity (1.37 W·m–1·K–1) than the single-filler filled SF (CF-SF, 1.2 W·m–1·K–1 or Al-SF, 0.52 W·m–1·K–1) under the same filling amount of 60 wt%. The finite element simulation was used further to explore the thermal conductive mechanism of the hybrid SF. Meanwhile, the compressive and tensile modulus of the material (CF-SF) was increased to 10.8 and 3.3 MPa compared with pure SF, respectively, and the mechanical properties were improved. In addition, infrared thermography further demonstrated that Al-CF-SF has a faster heat transfer rate under relaxation and applied pressure.

We have performed shrinkage restraint force measurements on three shape memory polymers of polyethylene terephthalate (PET), polymethyl methacrylate (PMMA) and a blend of the two at a range of temperatures. Observations are made of the change in stress during temperature rise, hold and cooling. All materials show an increase in stress during rise and hold, but on cooling, the three materials behave differently; the PET shows a drop in stress, the PMMA a rise and the blend a much smaller rise. This behaviour correlates with the reversible thermal dimensional change below the shrinkage threshold temperature; the expansion coefficients are negative for PET, positive for PMMA and positive at a lower order of magnitude for the blend. We model the behaviour by supposing that the shrinkage forces are created by prestressed strains effective at long range within a matrix of shorter chains effective at short range. The total stress is the sum of the shrinkage stress and the thermal stress in the matrix. The drops in stress on cooling are modelled using an elastic analysis based on measured elastic moduli and thermal expansion coefficients. For the blend, downward jumps in temperature produce small transient increases in the total stress, leaving it effectively unchanged. This phenomenon and the results of the elastic model for the stress drops imply that the shrinkage stress from the long-range chain network is largely unaffected by the temperature change and so is not entropic.

The present work describes, for the first time, the chemical modification and characterization of epoxy resins derived from Brazil nut oil (BNO). The development of a bio-based resin has been carried out by chemically modifying BNO, resulting in epoxidized Brazil nut oil (EBNO). Moreover, through a maleinization process, a crosslinker based on maleinized Brazil nut oil (MBNO) has been employed. Analysis using techniques like iodine value (IV) and oxirane oxygen content (Oo) indicate successful chemical modification. FTIR analysis confirms the presence of reactive functional groups in both EBNO and MBNO, which are responsible for resin crosslinking. Mechanical testing of the different bio-resins developed shows that, in the cured resins, flexural strength and modulus decrease with increasing MBNO content, indicating improved flexibility due to the introduction of MBNO as a crosslinker. Thermal analysis using differential scanning calorimetry (DSC) reveals exothermic peaks corresponding to resin curing appearing at progressively lower temperatures. Therefore, this study successfully modifies BNO and demonstrates its effectiveness as a precursor to develop bio-based epoxy resins. The resulting resins exhibit improved ductile and thermal properties, making them suitable for various applications requiring low mechanical stresses. [ABSTRACT FROM AUTHOR]

The main purpose of this work is to present the effect of long-chain branching and specific α-nucleation on the optical properties, crystallization and supermolecular structure of polypropylene (PP). Commercially available α-nucleating/clarifying agent 1,3;2,4-bis(3,4-dimethylbenzylidene)sorbitol (Millad 3988) was mixed into linear PP and long-chain branched PP (LCB-PP) in the concentration of 0.2 wt%. For the study of polymorphic composition, crystallinity, and crystallization process under isothermal conditions in the temperature range of 130–150 °C, differential scanning calorimetry and wide-angle X-ray scattering were used. Although the used nucleating/clarifying agent appears to have a slight effect on the optical properties of long-chain branched polypropylene, it does not appear to affect the crystallization kinetics significantly. LCB-PP exhibited self-nucleation, favored over nucleation by a specific nucleating agent.

Increasing demand for durable rubber and rapid advancement in the automotive sector has made oil-resistant rubber an increasingly important material. Among them, nitrile rubber (NBR) is the most iconic due to its extraordinary oil resistance contributed by the polar nitrile pendant groups. Synthesis of NBR, however, is highly hazardous due to the explosive nature of the gaseous monomer butadiene. In this work, poly(isoprene-co-acrylonitrile) (NIR) was synthesized using free radical emulsion polymerization, with liquid monomer isoprene as the diene in the rubber formulation. The spectroscopic analysis confirmed the formation of NIR and indicated that the polymerized isoprene in the rubber is predominantly of 1,4-microstructure. A series of rubbers with different contents of acrylonitrile were produced and the mechanical, thermal, as well as oil resistant property of the resultant rubber films were evaluated. Vulcanized NIR films displayed glass transition temperatures from –9.4 to 20.2 °C, suggesting that the polymers are rubbery at ambient and higher temperatures. The NIR rubber films exhibited excellent oil resistance with less than 2% swelling in mineral oil, good thermal stability with onset degradation temperature in the range of 361.3 to 369.9 °C, and adequate mechanical strength from 1.61 to 8.23 MPa. The synthesized NIR rubber has the potential to serve as an alternative to NBR which had been traditionally used for oil resistance applications.

In the global pursuit of using sustainable constituents for developing composite materials, the current investigation has paid particular attention to the most promising biopolymers, such as poly(lactic acid) (PLA) and bio-based poly(butylene succinate) (bio PBS). The research endeavor emphasizes a comparative assessment of short sisal fiber (SF) reinforced (10,20, and 30 wt%) PLA and bio PBS biocomposites. The analysis and discussion have been reported for the thermal, mechanical,crystallinity, and dynamic mechanical behavior of developed composite materials. Based on mechanical properties, the optimal fiber loading for SF/PLA and SF/bio PBS biocomposites was 20 and 30 wt%, respectively. The developed composites have shown a considerable improvement in crystallinity of 17.88 and 41.13% at 20 and 30 wt% of fiber loading in SF/PLA and SF/bio PBS, respectively. The maximum storage modulus values of 14.23 GPa (20SF/PLA) and 11.74 GPa (30SF/bio PBS) were observed. The loss modulus of the SF/PLA and SF/bio PBS composites was around 74 and 89% higher than the loss modulus of the PLA and the bio PBS matrix, respectively. Overall, composites fabricated with bio PBS (SF/bio PBS) have shown better crystallinity, thermal stability, and ease of processing than SF/PLA composites.

In the global pursuit of using sustainable constituents for developing composite materials, the current investigation has paid particular attention to the most promising biopolymers, such as poly(lactic acid) (PLA) and bio-based poly(butylene succinate) (bio PBS). The research endeavor emphasizes a comparative assessment of short sisal fiber (SF) reinforced (10, 20, and 30 wt%) PLA and bio PBS biocomposites. The analysis and discussion have been reported for the thermal, mechanical, crystallinity, and dynamic mechanical behavior of developed composite materials. Based on mechanical properties, the optimal fiber loading for SF/PLA and SF/bio PBS biocomposites was 20 and 30 wt%, respectively. The developed composites have shown a considerable improvement in crystallinity of 17.88 and 41.13% at 20 and 30 wt% of fiber loading in SF/PLA and SF/bio PBS, respectively. The maximum storage modulus values of 14.23 GPa (20SF/PLA) and 11.74 GPa (30SF/bio PBS) were observed. The loss modulus of the SF/PLA and SF/bio PBS composites was around 74 and 89% higher than the loss modulus of the PLA and the bio PBS matrix, respectively. Overall, composites fabricated with bio PBS (SF/bio PBS) have shown better crystallinity, thermal stability, and ease of processing than SF/PLA composites. [ABSTRACT FROM AUTHOR]

The influence of the reduction of macromolecular entanglements on the thermal and mechanical properties of polylactide composites containing 0.1–1.0 wt% of carbon nanotubes was investigated. Partial disentangling of the macromolecules improved the dispersion of the filler during composite fabrication. Greater mobility of less entangled polylactide macromolecules affected the crystallization of nanocomposites, which occurred already during the cooling of the melt and not only as a cold crystallization. Isothermal crystallization studies showed a beneficial combination of matrix disentanglement and increased nanotube nucleation, leading to much faster crystallization. In the entangled composite, crystallization at 120 °C was completed after 14 min, while in the partially disentangled composite only after 9 min. The reduction of entanglements of macromolecules also affected the mechanical properties. The plastic deformation was more easily initiated, and stresses in the strain-hardening phase increased more slowly during the deformation of disentangled homopolymers. In composites, the strain-hardening effect depended not only on the content of nanotubes but also on their dispersion, which was better in the less entangled polylactide matrix.

In this work, for the first time, the authors report polyethylene terephthalate (PET) track-etched membrane fabrication and detailed quantitative parametric studies for its application in He–N2 separation. The study also covers theoretical studies to understand the irradiation of PET film with ions as well as the contribution of gas flow domains, which is attempted for the first time. Monte Carlo simulations were carried out using the FLUKA code to evaluate the dose deposited by the ions in the PET film and the displacement per atom (DPA). The distribution of absorbed dose in the film as a function of thickness, the mean absorbed dose as a function of ion energy, and DPA at various depths in the film was determined using these simulations. The range of various ion beams was also calculated using the SRIM code. The effect of incident energy of irradiation beam (Si: 70 and 90 MeV and Cl: 84, 100 and 115 MeV) and etching parameters like concentration of NaOH, temperature, UV radiation, and ultrasonication on the control and irradiated polymer films (~25 μm thickness) were studied. Gas permeation studies of in-house synthesized track etched membrane (optimum) were carried out and a promising He/N2 selectivity of ~2.4 was achieved. The results confirmed that the membranes can have a potential application in the separation of He from natural gas.

Natural rubber (NR) vulcanizates with waste zinc oxide (ZnO) particles were prepared through a sulfur vulcanization process. This research aimed to investigate the effect of different ZnO sources as an activator: commercial ZnO (ZO), waste ZnO obtained from a ceramic industry (WZO), and calcinated WZO (C-WZO) on the properties of NR vulcanizates. The ZnO particles were characterized using X-ray fluorescence spectrometer, X-ray diffractometer, and transmission electron microscopy. It was found that the calcination at 800 °C for 6 h could reduce the sulfur components in WZO; consequently, the particle size and appearance were changed. For rubber vulcanizates, the composition of ZnO in the activator had an effect on the crosslink density of the obtained vulcanizates, resulting in changes to the mechanical tensile, thermal, and dynamic mechanical properties. The crosslink density, tensile strength, and tear strength of the rubber vulcanizate filled with C-WZO (NR/C-WZO (II), 0.18 mmol/cm3, 21.3 MPa, 68.4 N/mm, respectively) was acceptable for rubber products compared with those of the vulcanizate filled with ZO (NR/ZO, 0.19 mmol/cm3, 26.4 MPa, 71.6 N/mm, respectively). Accordingly, C-WZO could be used as an effective activator in rubber vulcanization.

This work reports on the development of polylactide (PLA)/mango kernel seed flour (MKSF) composites combined with tributyrin (TBN) and triacetin (TCN) as plasticizers. Thus, wood plastic composites (WPC) are obtained by extrusion and injection-molding processes. The solubility, mechanical, morphological, thermal, colorimetric, water absorbance, flowability, and disintegrability properties are evaluated. The ductility of the PLA+MKSF composite is improved by the plasticizing effect of TBN and TCN (10 phr (parts per hundred resin) each). Elongation at break is increased from 4.4 up to 9.5 and 8.3%, respectively. The theoretical solubility analysis supports the good miscibility between PLA with TBN and TCN (relative energy difference (RED) values of 0.86 and 0.73, respectively) deduced from the mechanical performance. Field emission scanning electron microscopy (FESEM) images also corroborate the mechanical findings, where a decrease in the presence of voids in the PLA matrix suggests certain compatibility between MKSF and TBN, and TCN. Differential scanning calorimetry (DSC) and dynamic-mechanical-thermal analysis (DMTA) results show that the plasticizers decrease the glass transition temperature and the melting temperature of PLA, thus improving its ductility. Thermogravimetric analysis (TGA) results indicate that the thermal stability of the composite is slightly decreased due to the relatively high volatility of the plasticizers, while MKSF does not affect this matter. The composites exhibit excellent biodegradability, presenting more than 90% of disintegration in compost soil conditions in 12 weeks. Finally, MKSF provided the composites with a wood-like dark brown color and with high water absorbance.

The influence of the reduction of macromolecular entanglements on the thermal and mechanical properties of polylactide composites containing 0.1-1.0 wt% of carbon nanotubes was investigated. Partial disentangling of the macromolecules improved the dispersion of the filler during composite fabrication. Greater mobility of less entangled polylactide macromolecules affected the crystallization of nanocomposites, which occurred already during the cooling of the melt and not only as a cold crystallization. Isothermal crystallization studies showed a beneficial combination of matrix disentanglement and increased nanotube nucleation, leading to much faster crystallization. In the entangled composite, crystallization at 120 °C was completed after 14 min, while in the partially disentangled composite only after 9 min. The reduction of entanglements of macromolecules also affected the mechanical properties. The plastic deformation was more easily initiated, and stresses in the strain-hardening phase increased more slowly during the deformation of disentangled homopolymers. In composites, the strain-hardening effect depended not only on the content of nanotubes but also on their dispersion, which was better in the less entangled polylactide matrix. [ABSTRACT FROM AUTHOR]

In this work, for the first time, the authors report polyethylene terephthalate (PET) track-etched membrane fabrication and detailed quantitative parametric studies for its application in He-N2 separation. The study also covers theoretical studies to understand the irradiation of PET film with ions as well as the contribution of gas flow domains, which is attempted for the first time. Monte Carlo simulations were carried out using the FLUKA code to evaluate the dose deposited by the ions in the PET film and the displacement per atom (DPA). The distribution of absorbed dose in the film as a function of thickness, the mean absorbed dose as a function of ion energy, and DPA at various depths in the film was determined using these simulations. The range of various ion beams was also calculated using the SRIM code. The effect of incident energy of irradiation beam (Si: 70 and 90 MeV and Cl: 84, 100 and 115 MeV) and etching parameters like concentration of NaOH, temperature, UV radiation, and ultrasonication on the control and irradiated polymer films (~25 µm thickness) were studied. Gas permeation studies of in-house synthesized track etched membrane (optimum) were carried out and a promising He/N2 selectivity of ~2.4 was achieved. The results confirmed that the membranes can have a potential application in the separation of He from natural gas. [ABSTRACT FROM AUTHOR]

Toughening efficiency of poly(ethylene-n-butylene-acrylate-co-glycidyl methacrylate) (EBA-GMA) in poly(lactic acid) (PLA) matrix has been found to significantly increase at elevated blending temperature. In the case of PLA/EBAGMA blends having 10.0 or 12.5 wt% EBA-GMA contents, the accelerated PLA degradation at raised processing temperature resulted in reduced mechanical performance. At 15.0 wt% EBA-GMA ratio, however, increased elongation and by 250% improved notched Izod impact strength was achieved when the blending temperature was raised from 240 to 260 °C. This beneficial effect is attributed to the accelerated compatibilization reactions between the components in the presence of shortchain PLA molecules, which allow the rapid formation of a toughening enhancer interphase (TEI) during melt processing. As a result, the brittle-ductile transition can be reached at lower elastomer content than expected. Decreased melt flow index (MFI) values besides stabilized blend morphology indicated efficient PLA–EBA-GMA compatibilization at elevated processing temperature. Accordingly, enhanced nucleation ability of the PLA/EBA-GMA interphase and hindered chain crystallization of PLA were found by differential scanning calorimetry (DSC) analyses. In association with the intensified compatibilization reactions cross-linking of the terpolymer was also revealed using the thermally stimulated depolarization current (TSDC) technique.

Polylactic acid (PLA) has shown two different crystalline structures, namely α and α′ when cooled down from the melt state. However, α-PLA has shown significant improvement in the barrier and mechanical properties of PLA. Although the effect of some nucleating agents on phase transformation of the PLA has been determined in the past, this is the first attempt, the effect of the starch nanocrystals on the formation of polymorphic crystal structure of PLA was evaluated. In this framework, the effect of lactic acid grafted starch nanocrystals (SNCs-g-LA) concentrations on the phase transition, and crystallization behavior of PLA/SNCs-g-LA nanocomposites at different isothermal crystallization temperatures (Tc) were studied. The results indicate that SNCs-g-LA nanoparticles promote the degree of crystalline transition to yield the highly crystalline ordered α-PLA. Further, the half-time crystallization (t1/2) of PLA composites was calculated by the Avrami equation. The t1/2 of PLA was minimum by adding 5 wt% SNCs-g-LA nanoparticles, and it decreased from 10.4 to 3.9 min. The growth rate of the spherulite morphology of PLA composites showed a significant improvement in the crystalline structure of PLA/SNCs-g-LA (5 wt%) nanocomposites as well. Finally, small angle X-ray scatting (SAXS) analysis showed that the inclusion of 5 wt% grafted SNCs resulted in the increment of the long period (Lac) as well as crystal layer thickness (Lc).

Natural rubber (NR) vulcanizates with waste zinc oxide (ZnO) particles were prepared through a sulfur vulcanization process. This research aimed to investigate the effect of different ZnO sources as an activator: commercial ZnO (ZO), waste ZnO obtained from a ceramic industry (WZO), and calcinated WZO (C-WZO) on the properties of NR vulcanizates. The ZnO particles were characterized using X-ray fluorescence spectrometer, X-ray diffractometer, and transmission electron microscopy. It was found that the calcination at 800 °C for 6 h could reduce the sulfur components in WZO; consequently, the particle size and appearance were changed. For rubber vulcanizates, the composition of ZnO in the activator had an effect on the crosslink density of the obtained vulcanizates, resulting in changes to the mechanical tensile, thermal, and dynamic mechanical properties. The crosslink density, tensile strength, and tear strength of the rubber vulcanizate filled with C-WZO (NR/C-WZO (II), 0.18 mmol/cm³, 21.3 MPa, 68.4 N/mm, respectively) was acceptable for rubber products compared with those of the vulcanizate filled with ZO (NR/ZO, 0.19 mmol/cm³, 26.4 MPa, 71.6 N/mm, respectively). Accordingly, C-WZO could be used as an effective activator in rubber vulcanization. [ABSTRACT FROM AUTHOR]

This work reports on the development of polylactide (PLA)/mango kernel seed flour (MKSF) composites combined with tributyrin (TBN) and triacetin (TCN) as plasticizers. Thus, wood plastic composites (WPC) are obtained by extrusion and injection-molding processes. The solubility, mechanical, morphological, thermal, colorimetric, water absorbance, flowability, and disintegrability properties are evaluated. The ductility of the PLA+MKSF composite is improved by the plasticizing effect of TBN and TCN (10 phr (parts per hundred resin) each). Elongation at break is increased from 4.4 up to 9.5 and 8.3%, respectively. The theoretical solubility analysis supports the good miscibility between PLA with TBN and TCN (relative energy difference (RED) values of 0.86 and 0.73, respectively) deduced from the mechanical performance. Field emission scanning electron microscopy (FESEM) images also corroborate the mechanical findings, where a decrease in the presence of voids in the PLA matrix suggests certain compatibility between MKSF and TBN, and TCN. Differential scanning calorimetry (DSC) and dynamic-mechanical-thermal analysis (DMTA) results show that the plasticizers decrease the glass transition temperature and the melting temperature of PLA, thus improving its ductility. Thermogravimetric analysis (TGA) results indicate that the thermal stability of the composite is slightly decreased due to the relatively high volatility of the plasticizers, while MKSF does not affect this matter. The composites exhibit excellent biodegradability, presenting more than 90% of disintegration in compost soil conditions in 12 weeks. Finally, MKSF provided the composites with a wood-like dark brown color and with high water absorbance. [ABSTRACT FROM AUTHOR]

The current paper addresses the network-formation process of an epoxy polymer focussing on transition phenomena like the percolation threshold and the chemically induced glass transition. Based on a single type of measurement, different kinds of volume changes are used as sensitive probes to the morphological changes accompanying the polymerization process. Thereby, the rather new experimental technique of ‘Temperature Modulated Optical Refractometry’ (TMOR) allows to simultaneously obtain not only the volume shrinkage and the accompanying dynamic thermal volume expansion in the course of polymerization, but also the chemical turnover as a function of the refractive index. In order to test the applicability of the refractive index as a reasonable quantity to substitute respective infrared spectroscopy (IR) measurements, the network-formation is induced by homopolymerization reactions to specifically limit the degree of cure to a single spectral IR component. This countercheck is performed using IR by attenuated total reflection (ATR). Whereas the chemical-induced glass transition is clearly evidenced by the different kinds of volume changes, the percolation transition does not couple to these properties. However, the transition to the glassy state is highly variable and leads to large differences of the macromolecular-induced morphologies.

In this work, new furan-based poly(ester amide)s of various compositions were synthesised by the melt polycondensation method. The chemical structure and composition were determined by nuclear magnetic resonance spectroscopy (1H NMR) and Fourier transform infrared (FTIR) analyses. The optical properties were studied by UV-Vis spectroscopy. The thermal properties were investigated by means of differential scanning calorimetry (DSC). The thermo-oxidative stability of PEAs was also tested. Additionally, the free volume by positron annihilation lifetime spectroscopy (PALS) technique and mechanical properties were examined. It was found that the incorporation of poly(propylene furanamide) (PPAF) units significantly affects the thermal and mechanical properties of co-polymers based on poly(hexylene 2,5-furandicarboxylate) (PHF). Depending on the composition, both semi-crystalline and amorphous co-polymers were obtained. Moreover, the values of the free volume radius (R) and the free volume fractions (fv) were strongly affected by the mole fraction of PPAF units.

Core-shell thermally expandable microspheres (TEMs) were prepared via Pickering suspension polymerization. Acrylonitrile (AN), methacrylic acid (MAA) and N,N-dimethylacrylamide (DMAA) were used as the comonomers, the 2,2′-azobisisobutyronitrile (AIBN) was used as the initiator and the ethyleneglycol dimethacrylate (EGDMA) was used as the crosslinker. The effects of initiator concentration, cross-linking agent concentration and modified monomer type on the morphology, thermal properties and encapsulation content of TEMs were investigated. The results show that the small change in initiator concentration had a significant effect on the properties of TEMs. When the initiator concentration was 0.55%, the microspheres showed core-shell structure and the maximum expansion ratio was 3.06 times. According to the scanning electron microscope (SEM) image, the heat resistance of the microspheres increased with the increase of the content of crosslinking agent. The lower the water solubility of the modified monomer, the more stable the foaming of the TEMs. When methyl acrylate (MA) was used as a modified monomer, the initial expansion temperature of the microspheres was 163.2°C, the maximum expansion temperature was 223.5 °C, and the encapsulation content of the blowing agent was 14.70%.

Toughening efficiency of poly(ethylene-n-butylene-acrylate-co-glycidyl methacrylate) (EBA-GMA) in poly(lactic acid) (PLA) matrix has been found to significantly increase at elevated blending temperature. In the case of PLA/EBA-GMA blends having 10.0 or 12.5 wt% EBA-GMA contents, the accelerated PLA degradation at raised processing temperature resulted in reduced mechanical performance. At 15.0 wt% EBA-GMA ratio, however, increased elongation and by 250% improved notched Izod impact strength was achieved when the blending temperature was raised from 240 to 260 °C. This beneficial effect is attributed to the accelerated compatibilization reactions between the components in the presence of shortchain PLA molecules, which allow the rapid formation of a toughening enhancer interphase (TEI) during melt processing. As a result, the brittle-ductile transition can be reached at lower elastomer content than expected. Decreased melt flow index (MFI) values besides stabilized blend morphology indicated efficient PLA--EBA-GMA compatibilization at elevated processing temperature. Accordingly, enhanced nucleation ability of the PLA/EBA-GMA interphase and hindered chain crystallization of PLA were found by differential scanning calorimetry (DSC) analyses. In association with the intensified compatibilization reactions cross-linking of the terpolymer was also revealed using the thermally stimulated depolarization current (TSDC) technique. [ABSTRACT FROM AUTHOR]

Polylactic acid (PLA) has shown two different crystalline structures, namely a and a' when cooled down from the melt state. However, a-PLA has shown significant improvement in the barrier and mechanical properties of PLA. Although the effect of some nucleating agents on phase transformation of the PLA has been determined in the past, this is the first attempt, the effect of the starch nanocrystals on the formation of polymorphic crystal structure of PLA was evaluated. In this framework, the effect of lactic acid grafted starch nanocrystals (SNCs-g-LA) concentrations on the phase transition, and crystallization behavior of PLA/SNCs-g-LA nanocomposites at different isothermal crystallization temperatures (Tc) were studied. The results indicate that SNCs-g-LA nanoparticles promote the degree of crystalline transition to yield the highly crystalline ordered a-PLA. Further, the half-time crystallization (t1/2) of PLA composites was calculated by the Avrami equation. The t1/2 of PLA was minimum by adding 5 wt% SNCs-g-LA nanoparticles, and it decreased from 10.4 to 3.9 min. The growth rate of the spherulite morphology of PLA composites showed a significant improvement in the crystalline structure of PLA/SNCs-g-LA (5 wt%) nanocomposites as well. Finally, small angle X-ray scatting (SAXS) analysis showed that the inclusion of 5 wt% grafted SNCs resulted in the increment of the long period (Lac) as well as crystal layer thickness (Lc). [ABSTRACT FROM AUTHOR]

Vinylsilane grafted carbon nanotubes (VCNTs) can act as reactive compatibilizers for cocontinuous poly(lactic acid)/high-density polyethylene (PLA/HDPE) blends, with the aid of organic peroxides initiated radical reactions. The reactively compatibilized PLA/HDPE/VCNTs blend nanocomposites exhibit strong interfacial interactions, as can be reflected by the remarkably increased storage modulus at low frequencies. Due to strong interfacial interactions, the VCNTs act as highly efficient nucleating agents for the PLA component. With 2.0 wt% of VCNTs, the crystallinity of PLA component reaches a value of 33.8% after melt cooling, and thus cold crystallization can no longer be observed upon heating. Thanks to the high crystallinity of the PLA component, the reactively compatibilized blend nanocomposite with 2.0 wt% of VCNTs shows a much higher elastic modulus than those of pristine PLA/HDPE blends and uncompatibilized blend nanocomposites in the temperature range of 60 to 80°C. Moreover, the reactively compatibilized blend nanocomposites exhibit an obvious increase trend in tensile strength with increasing the content of VCNTs, due to stronger interfacial interactions. This work provides a generic strategy for compatibilizing and reinforcing immiscible polymer blend nanocomposites using reactive carbon nanotubes.

This work is a first attempt to study the crystallization behavior of ethylene-vinyl alcohol copolymer with 44 mol% of ethylene units (EVOH44) and to observe the supermolecular structures developed during its crystallization. Thermal analysis has evidenced a very fast crystallization and the formation of different crystal populations during isothermal crystallization. In-situ wide-angle X-ray scattering experiments using a synchrotron radiation source have shown a unique orthorhombic morphology, independently of the crystallization conditions. Small spherulites (with an average radius of about 1 μm) were observed using polarized optical microscopy and confirmed by typical four-leaf patterns obtained by small-angle light scattering. In-situ atomic force microscopy has revealed stacked lamellae growing from common centers to form small spherulitic entities. Finally, studies of isothermal crystallization have evidenced the existence of partial crystallization (especially at high crystallization temperatures) and the need for higher undercooling to complete crystallization.

In this work, new furan-based poly(ester amide)s of various compositions were synthesised by the melt polycondensation method. The chemical structure and composition were determined by nuclear magnetic resonance spectroscopy (1H NMR) and Fourier transform infrared (FTIR) analyses. The optical properties were studied by UV-Vis spectroscopy. The thermal properties were investigated by means of differential scanning calorimetry (DSC). The thermo-oxidative stability of PEAs was also tested. Additionally, the free volume by positron annihilation lifetime spectroscopy (PALS) technique and mechanical properties were examined. It was found that the incorporation of poly(propylene furanamide) (PPAF) units significantly affects the thermal and mechanical properties of co-polymers based on poly(hexylene 2,5-furandicarboxylate) (PHF). Depending on the composition, both semi-crystalline and amorphous co-polymers were obtained. Moreover, the values of the free volume radius (R) and the free volume fractions (fv) were strongly affected by the mole fraction of PPAF units. [ABSTRACT FROM AUTHOR]

Methacrylic copolymers have high potential as matrix polymers for carbon fiber reinforced thermoplastics (CFRTPs) due to their superior mechanical properties and the versatility of the monomers. However, the methacrylic copolymers have low solvent resistance, compared to epoxy, polyamide, and polypropylene, due to their un-cross-linked amorphous structure. Therefore, an improvement of the solvent resistance by the introduction of metal salts into methacrylic copolymer matrices for CFRTPs was investigated. Infrared spectroscopy, dynamic mechanical analyses and small-angle X-ray scattering clarified that an ionic cross-linked structure was formed. Low-viscosity mixtures of the methacrylic monomers with the metal salts, as a precursor of the matrices for CFRTPs, were easily impregnated into CF fabrics and were then copolymerized within the CF fabrics. Both the flexural strength and shear adhesive strength of the CFRTPs using the in situ polymerized methacrylic ionomer cross-linked with sodium ions were sufficiently high, even after 12 h immersion in methyl ethyl ketone.

In this study, graphene nanoplatelets (GNPs) were synthesized from graphite by a liquid-phase exfoliation (layer separation) method, and their surfaces were functionalized with poly(glycidyl methacrylate) (PGMA) by using the rotatingbed plasma-enhanced chemical vapor deposition (PECVD) method. Fourier-transform infrared spectroscopy (FT-IR), Raman spectroscopy, scanning electron microscopy (SEM), X-ray powder diffraction (XRD), and thermogravimetric (TGA) analyses were performed to characterize the unmodified (u-GNP) and modified GNP (PGMA-GNP). Epoxy nanocomposites were prepared with both types of GNPs at different loading levels (0.1–2% by weight). The role of the surface modification of the GNPs on the mechanical, thermal, electrical conductivity, contact angle, water sorption, and corrosion properties of the epoxy nanocomposite coatings was also investigated. Consequently, the tensile strength and Young’s modulus of the epoxy resin (ER)/PGMA-GNP nanocomposites were enhanced by 10.2–20 and 3.3–18.4%, respectively, as compared to the ER/u-GNP composites. Moreover, the nanocomposites prepared with PGMA-GNP had better water sorption and wettability properties than those prepared with u-GNP, but lower electrical conductivity. The corrosion test results showed that the addition of GNPs to epoxy effectively improved the corrosion resistance of the epoxy composites in high salinity, basic, and acidic environments.

Preparing an epoxy resin with biomass resources as an alternative for bisphenol A is significant for sustainable and renewable development under great pressure of limited fossil resources and urgent environmental issues. Herein, we synthesized an epoxy oligomer P-DBP-EP-n derived from biomass magnolol through an efficient one-step glycidylation. P-DBP-EP-n exhibited a low viscosity of 11.7 Pa・s at room temperature, endowing it with excellent processability as diglycidyl ether of bisphenol A (DGEBA) and magnolol-based epoxy monomer EDBP. Then P-DBP-EP-n was cured with a diamine curing agent, 4,4′-diaminodiphenyl methane (DDM), and following thermal addition polymerization of allyl units. Compared with DGEBA/DDM and EDBP/DDM, P-DBP-EP-n/DDM possessed a higher glass transition temperature (Tg) (304 to 167 and 226 °C), implying distinguished heat resistance. Furthermore, the tensile properties and notched impacted strength of P-DBP-EP-n/DDM were better than EDBP/DDM (20.7 to 19.4 MPa, 2.0 to 1.6 GPa, and 2.5 to 2.0 kJ/m2). The initial degradation temperature and char residue of P-DBP-EP-n/DDM were 421 °C and 35.2%, with a 13.5 and 101% increase compared with those of DGEBA/DDM, respectively. Additionally, P-DBP-EP-n/DDM displayed outstanding flame retardancy with V-0 rate for the vertical burning test and limiting oxygen index value of 47.7%, which was almost twice as much as that of DGEBA/DDM. This study offers a promising and feasible pathway to obtain a fully bio-based epoxy resin substituted for petroleum-based DGEBA with distinguished processability, heat resistance, and flame retardancy. Comprehensive properties of the bio-based thermosets are expected to be further regulated by the thermal addition polymerization of allyl units.

Colorless and transparent polymer films and sheets with good high-temperature resistance and low dielectric constant (low-Dk) and low dissipation factors (low-Df) features are highly desired in advanced optoelectronic integrated circuits (OEIC) fabrications. In the current work, a series of semi-alicyclic polyimide (PI) powders were first prepared by the onestep high-temperature polycondensation of an alicyclic dianhydride, hydrogenated 3,3′,4,4′-biphenyl tetracarboxylic dianhydride (HBPDA) and aromatic diamines which were beneficial for endowing the derived PI films with low-Dk features, including 2,2-bis[4-(4-aminophenoxy)phenyl]propane (BAPP) for PI-1, 2,2-bis[4-(4-aminophenoxy)phenyl]hexafluoropropane (BDAF) for PI-2, and 9,9-bis[4-(4-aminophenoxy)phenyl]fluorene (BAOFL) for PI-3. Then, the derived PI powders were fabricated into colorless films and light-colored sheets, respectively. The freestanding flexible and tough PI films showed excellent optical transparency with the ultraviolet (UV) cutoff wavelength (λcut) lower than 300 nm, the optical transmittance higher than 85% at the wavelength of 400 nm, yellow indices (b*) lower than 1.0, and haze values lower than 1.2%. The hot-processed PI sheets also exhibited light colors. The PI films and sheets showed good thermal stability with the glass transition temperatures (Tg) higher than 220 °C. More importantly, the derived semi-alicyclic PI sheets showed Dk and Df values as low as 2.56 and 0.008 at 1 MHz, respectively.

In this paper, phenolic resin hollow microspheres (PHM) were prepared using in-situ polymerization and used as flame-retardants for TPU. The structure and composition of PHM were characterized by Scanning Electron Microscope (SEM). The potential of PHM as flame retardant was verified by thermogravimetric analysis (TG). Then, the flame retardancy and toxicity reduction of PHM in TPU/PHM composites were verified by cone calorimeter test (CCT) and Thermogravimetric Analysis-infrared Spectrometry (TG-IR). It has been found that comparing TPU/PHM-4 sample containing 4.0 wt% PHM with pure TPU, the peak heat release rate (pHRR) was reduced by 61.6%, the total smoke release (TSR) by 23.2%, and the CO production by 86.2%, respectively. The SEM, Laser Raman Spectroscopy Test (LRS), and other tests were carried out to test the char residues after CCT, and the mechanism of PHM in the process of flame retardant TPU was reasonably deduced. In a word, PHM is very effective as a flame retardant of TPU.

In this work, the crosslinking reaction of epoxidized natural rubber (50 mol% epoxy, ENR-50) by metal ion namely ferric ion (Fe3+, FeCl3, ferric chloride) was studied. It was found that a direct interaction of the ferric ion with the epoxy group as well as internal polymerization enable the ENR to be efficiently cured. The vulcanizing ENR-FeCl3 compound was then reinforced by carbon nanotubes (CNTs). The FTIR spectra of ENR-FeCl3 compounds without and with CNTs show the absorption peak at the wavenumber 470 cm-1, which represents the -O-Fe-O- linkages from a reaction of FeCl3 and opened oxirane ring products of ENR molecules. Furthermore, the ENR-FeCl3 compounds show a typical marching curing curve with a steady increase in torque as increasing of the testing time; especially the effect is more pronounced in CNTs filled system. Furthermore, an increase in the concentration of CNTs causes increasing in torque difference and enhancement of the mechanical properties (i.e., 100% moduli and tensile strength). The SEM micrograph shows good compatibility between CNTs and the rubber matrix in the ENR-FeCl3 compounds. Also, the electrical conductivities of ENR-FeCl3/CNTs nanocomposite increases with the increase of CNTs loading. It is also observed that the degradation temperature (Td) of ENR-FeCl3/CNTs is shifted toward a higher temperature range with the increase of the CNTs loadings. [ABSTRACT FROM AUTHOR]

A new simple system to vulcanize natural rubber (NR) latex at low temperature (50°C) using different bifunctional aldehydes has been proposed. Bifunctional aldehydes with different number of carbon atoms present in the chemical structure, including glyoxal (GX) with 2 carbon atoms, glutaraldehyde (GA) with 5 carbon atoms and phthaldialdehyde (PA) with 8 carbon atoms were added into natural rubber latex. The mechanical, thermal and optical properties of the crosslinked NR were studied. The formation of crosslinking in the cured NRs was confirmed using infrared spectroscopy (ATR-FTIR). A new absorption peak was found at 1589 cm-1 for -NH bending of secondary amine in the case of cured NRs when compared to uncured NR. Universal testing machine (UTM), dynamic mechanical thermal analysis (DMA), thermogravimetric analyzer (TGA) and temperature scanning stress relaxation (TSSR) were employed to study the tensile and thermal properties of cured NRs. Results revealed that the GA cured NR exhibited superior mechanical properties in terms of 100% modulus, tensile strength and hardness up to 2.13, 6.38 MPa and 54.67 Shore A, respectively. Furthermore, GA cured NR showed the highest crosslink density (72.40 mol/m³) and also showed better thermal properties among the different curing systems. The optical properties in terms of transparency of cured NRs were studied. It was noticed that PA cured NR gave more transparency and hence it can be introduced in developing materials for sensor applications. [ABSTRACT FROM AUTHOR]

Novel materials with neutron shielding property were fabricated by incorporating boron compounds into high-density polyethylene (HDPE)/Ethylene propylene diene monomer rubber (EPDM) blends. A detailed investigation on the morphological, thermal, mechanical, and neutron attenuation properties of suitable proportion of HDPE/EPDM blend with boric acid (BA), boron carbide (BC), and nano boron carbide (NBC) were performed. Morphology of the 20 wt% of EPDM shows better distribution in HDPE matrix. BA filler is localised in the HDPE phase, while NBC shows uniform distribution in HDPE/EPDM blend compared to its micro counterpart. There is a reduction in the tensile strength and modulus with the incorporation of EPDM in HDPE, whereas the ductility of HDPE is enhanced. A significant increase in the tensile toughness of the HDPE/EPDM blend with lower tensile strength and modulus is observed for BA, and BC filled composites. Moreover, HDPE/EPDM composites with NBC show only a marginal increase in the tensile toughness, tensile strength, and modulus. Comparison of the Young's modulus of the HDPE/EPDM blends with theoretical models indicates trends similar to the Coran model. The BA and BC filled composites follow the lower bound series model, whereas NBC composites show behaviour similar to the Halpin Tsai model. Total thermal neutron macroscopic cross-section (0.025 MeV energy neutrons) of 10 cm-1 and mean free path of 0.1 cm was obtained for 20 wt% NBC HDPE/EPDM composites. [ABSTRACT FROM AUTHOR]

This work is a first attempt to study the crystallization behavior of ethylene-vinyl alcohol copolymer with 44 mol% of ethylene units (EVOH44) and to observe the supermolecular structures developed during its crystallization. Thermal analysis has evidenced a very fast crystallization and the formation of different crystal populations during isothermal crystallization. In-situ wide-angle X-ray scattering experiments using a synchrotron radiation source have shown a unique orthorhombic morphology, independently of the crystallization conditions. Small spherulites (with an average radius of about 1 µm) were observed using polarized optical microscopy and confirmed by typical four-leaf patterns obtained by smallangle light scattering. In-situ atomic force microscopy has revealed stacked lamellae growing from common centers to form small spherulitic entities. Finally, studies of isothermal crystallization have evidenced the existence of partial crystallization (especially at high crystallization temperatures) and the need for higher undercooling to complete crystallization. [ABSTRACT FROM AUTHOR]

In this work, a series of reactive in-situ polyurethane (PU) nanocomposites based on the triblock copolymer of PCL1000-PEG1000-PCL1000, chemically cross-linked by hydroxyl-functionalized MWCNTs (um-MWCNT) and PCL-grafted MWCNTs (mod-MWCNT), were synthesized. In order to optimize the shape memory performance, crystallization mechanisms of the soft domains were tuned. The nanoparticles, acting as phase controller of the block copolymer, affected the chain’s confinement and crystals’ morphology leading to a wide range of shape fixity (84–100%) and shape recovery (78–97%) ratios. Non-isothermal crystallization studies revealed that using mod- MWCNTs increased the melting temperature (Tm) as an indication of higher thermal stability of the formed crystallites. Moreover, isothermal DSC measurements, fitted to the Avrami equation, were used to measure the changes in the growth rate and morphological features of the formed crystallites. The results indicated an increase in Avrami exponent (n) from 1.43 to 3.11, and crystallization half-time (t0.5) decreased from 6.16 to 2.67 minutes for crystallization temperature (Tc) of –25 °C, attributed to the effect of PCL grafts on PUs’ microstructure. In addition, the results of cell viability, evaluated by HFF cells, proved a proper cytocompatibility. Culturing hMSCs also showed good adhesion and cell spreading, as a function of hydrophilicity. The optimum sample, containing 0.5% PCL-g-MWCNT, showed 97% shape recovery at body temperature (37°C).

Biochar has emerged as a filler material for bio-degradable composites with favorable thermal and mechanical properties. Therefore, biochar is used in poly (lactic acid) (PLA) and PLA/thermoplastic starch (TPS) based composites. The crystallization and thermo-analytical properties of these blends with increasing amounts (20 to 50 wt%) of biochar are investigated. In the thermogravimetric analysis, the PLA/char composites’ onset degradation temperature and temperature of maximum weight loss decrease with increasing biochar concentrations (320 to 275 °C and 380 to 350 °C, respectively). Contrastingly, in the PLA/TPS/char composites, the impact of the biochar is shielded by the TPS. The unaltered glass transition demonstrates that biochar does not act as a plasticizer in any of the composites, while TPS does. Biochar acts as a nucleation agent, but hinders further crystal growth at high concentrations, as confirmed by isothermal crystallization and infrared spectroscopy. The TPS smoothens the PLA/biochar interface, leading to an obstructed nucleation effect of biochar, proven by differential scanning calorimetry, infrared spectroscopy, and scanning electron microscopy. This work demonstrates the shielding effect TPS has on biochar and can help to understand further and optimize the production and biodegradability of these composites.

This study aims to investigate the effect of different carbonaceous fillers, carbon black (CB) biocarbon (BC), and a hybrid filler of both (BC-CB), in a natural rubber matrix. It was found that the addition of hybrid filler based on a sustainable biocarbon (BC) and carbon black (CB) revealed a significant effect on reducing the rolling resistance properties. Dried distillers’ grain with solubles (DDGS), a co-product from corn ethanol industry pyrolyzed at 900 °C, was used to produce the biocarbon. As compared to the carbon black, the particle size of the biocarbon was larger which was reflected in the tensile strength of the biocarbon composites. This observation was correlated using swelling studies and found to be proportional to their crosslink density. The thermal characterizations showed similar transitions and degradation mechanisms in all the composites, which confirmed a comparatively similar behavior of BC with CB. Moreover, these findings justify further tuning of biocarbon into nanosize and this could expand the scope in the utilization of this sustainable filler for the fabrication of various rubber products such as tires and hoses, etc.

Preparing an epoxy resin with biomass resources as an alternative for bisphenol A is significant for sustainable and renewable development under great pressure of limited fossil resources and urgent environmental issues. Herein, we synthesized an epoxy oligomer P-DBP-EP-n derived from biomass magnolol through an efficient one-step glycidylation. P-DBP-EP-n exhibited a low viscosity of 11.7 Pa·s at room temperature, endowing it with excellent processability as diglycidyl ether of bisphenol A (DGEBA) and magnolol-based epoxy monomer EDBP. Then P-DBP-EP-n was cured with a diamine curing agent, 4,4'-diaminodiphenyl methane (DDM), and following thermal addition polymerization of allyl units. Compared with DGEBA/DDM and EDBP/DDM, P-DBP-EP-n/DDM possessed a higher glass transition temperature (Tg) (304 to 167 and 226 °C), implying distinguished heat resistance. Furthermore, the tensile properties and notched impacted strength of P-DBP-EP-n/DDM were better than EDBP/DDM (20.7 to 19.4 MPa, 2.0 to 1.6 GPa, and 2.5 to 2.0 kJ/m²). The initial degradation temperature and char residue of P-DBP-EP-n/DDM were 421 °C and 35.2%, with a 13.5 and 101% increase compared with those of DGEBA/DDM, respectively. Additionally, P-DBP-EP-n/DDM displayed outstanding flame retardancy with V-0 rate for the vertical burning test and limiting oxygen index value of 47.7%, which was almost twice as much as that of DGEBA/DDM. This study offers a promising and feasible pathway to obtain a fully bio-based epoxy resin substituted for petroleum-based DGEBA with distinguished processability, heat resistance, and flame retardancy. Comprehensive properties of the bio-based thermosets are expected to be further regulated by the thermal addition polymerization of allyl units. [ABSTRACT FROM AUTHOR]

Thermoplastic natural rubber (TPNR) nanocomposites based on epoxidized natural rubber (ENR) and polypropylene (PP) blends filled with 2.5 wt% nano-silica (SiO2) were prepared using a two-step compounding process to improve the dispersion of SiO2 in TPNR. The effects of the compounding techniques, i.e., solid pre-compounding and latex pre-compounding processes of SiO2 and ENR, and surface modification of SiO2 on the morphological, mechanical, and thermal properties together with the crystallization behavior of PP phase in ENR/PP blends were demonstrated. Scanning electron microscope (SEM) results showed that latex pre-compounding of SiO2 and ENR gave finer dispersion and distribution of SiO2 particles in the TPNR matrix as compared with the solid pre-compounding technique. Also, the superior mechanical properties and thermal stability of the blends were achieved by using the latex pre-compounding technique. Moreover, surface modification of SiO2 by organosilane was found to enhance crystallization rate and the degree of crystallinity of PP phase in the TPNR, leading to an improvement in the strength and mechanical properties of the ENR/PP blends. These results agree well with the morphological properties that presented a good dispersion and distribution of silane-modified SiO2 particles in the TPNR matrix. [ABSTRACT FROM AUTHOR]

The influence of long-chain branching and specific β-nucleation on polymorphic composition, melting and crystallization, and morphology of polypropylene blends were investigated by wide-angle X-ray scattering, differential scanning calorimetry, and scanning electron microscopy. Linear polypropylene and long-chain branched polypropylene were used for the preparation of blends in various proportions. N,N′-dicyclohexylnaphthalene-2,6-dicarboxamide was introduced (0 or 0.03 wt%) as a β-specific nucleating agent into prepared blends. It was found that LCB-PP strongly induces γ-phase formation in the blends and suppresses the nucleation activity of a β-specific nucleating agent. Blends containing a predominant amount of α- and γ-phases showed higher thermodynamic stability within melting, as compared to the samples rich in β-phase. During crystallization, LCB-PP in the blends increases nucleation density by self-seeding effect, manifesting itself in the shift of crystallization temperature. β-phase in the blends is distinctly separated in spherulites, while α- and γ-phases coexist on the lamellae level.

Colorless and transparent polymer films and sheets with good high-temperature resistance and low dielectric constant (low-Dk) and low dissipation factors (low-Df) features are highly desired in advanced optoelectronic integrated circuits (OEIC) fabrications. In the current work, a series of semi-alicyclic polyimide (PI) powders were first prepared by the onestep high-temperature polycondensation of an alicyclic dianhydride, hydrogenated 3,3',4,4'-biphenyl tetracarboxylic dianhydride (HBPDA) and aromatic diamines which were beneficial for endowing the derived PI films with low-Dk features, including 2,2-bis[4-(4-aminophenoxy)phenyl]propane (BAPP) for PI-1, 2,2-bis[4-(4-aminophenoxy)phenyl]hexafluoropropane (BDAF) for PI-2, and 9,9-bis[4-(4-aminophenoxy)phenyl]fluorene (BAOFL) for PI-3. Then, the derived PI powders were fabricated into colorless films and light-colored sheets, respectively. The freestanding flexible and tough PI films showed excellent optical transparency with the ultraviolet (UV) cutoff wavelength (λcut) lower than 300 nm, the optical transmittance higher than 85% at the wavelength of 400 nm, yellow indices (b*) lower than 1.0, and haze values lower than 1.2%. The hot-processed PI sheets also exhibited light colors. The PI films and sheets showed good thermal stability with the glass transition temperatures (Tg) higher than 220 °C. More importantly, the derived semi-alicyclic PI sheets showed Dk and Df values as low as 2.56 and 0.008 at 1 MHz, respectively. [ABSTRACT FROM AUTHOR]

In this paper, phenolic resin hollow microspheres (PHM) were prepared using in-situ polymerization and used as flame-retardants for TPU. The structure and composition of PHM were characterized by Scanning Electron Microscope (SEM). The potential of PHM as flame retardant was verified by thermogravimetric analysis (TG). Then, the flame retardancy and toxicity reduction of PHM in TPU/PHM composites were verified by cone calorimeter test (CCT) and Thermogravimetric Analysis-infrared Spectrometry (TG-IR). It has been found that comparing TPU/PHM-4 sample containing 4.0 wt% PHM with pure TPU, the peak heat release rate (pHRR) was reduced by 61.6%, the total smoke release (TSR) by 23.2%, and the CO production by 86.2%, respectively. The SEM, Laser Raman Spectroscopy Test (LRS), and other tests were carried out to test the char residues after CCT, and the mechanism of PHM in the process of flame retardant TPU was reasonably deduced. In a word, PHM is very effective as a flame retardant of TPU. [ABSTRACT FROM AUTHOR]

A triazine-based functional monomer (AET) was synthesized via a nucleophilic substitution reaction between cyanuric chloride and 3-aminophenylacetylene. The comprehensive properties were superior, including simple synthesis conditions, moderate curing conditions, excellent thermal properties, and good mechanical properties of laminated composites comprised of AET and quartz fiber. The curing reaction showed high reactivity and low temperature, an activation energy of 106.33 kJ・mol–1 and cure exothermic peak between 140 and 250 °C with an enthalpy of 780 J・g–1. The decomposition temperature at 5% mass loss was 521 °C, the char yield at 800 °C was 78% and the glass transition temperature was 470 °C. Moreover, QF/P-AET laminated composite possessed good mechanical properties. The flexural strength was 364.94 Mpa and the interlaminar shear strength was 30.4 MPa at room temperature (RT); especially at 300 and 500 °C, the composite still displayed a high mechanical strength retention of up to 66 and 88, and 45 and 42%, respectively which is unachievable for cyanate and aryl acetylene resins. All above attracting properties make AET a good candidate as a matrix for high performance polymeric composite materials.

The present study deals with the incorporation of different ratios of alkali-treated coir fibres (CF) and pineapple leaf fibres (PALF) in polylactic acid (PLA) hybrid composites. Developed hybrid composites are characterized in terms of mechanical, morphological, thermal and physical properties. Mechanical characterization revealed that alkali-treated C3P7 hybrid composites (CF:PALF = 3:7) showed highest tensile strength (30.29 MPa) and young’s modulus (5.16 GPa) among all hybrids composites, whereas C1P1 (CF:PALF = 1:1) showed highest impact properties. Scanning electron microscopy (SEM) justified the consequence of alkali treatment on fibre-matrix adhesion. Thermal analysis revealed that C1P1 and C7P3 (CF:PALF = 7:3) having a higher thermal stability and char content due to the higher content of lignin in CF. Remarkably, the coefficient of thermal expansion (CTE) of treated hybrid composites displayed lesser values than untreated hybrid composites. The physical tests revealed that C3P7 showed highest water absorption (WA) and thickness swelling (TS) though after treatment the WA and TS values get reduced. Overall results indicated that treated CF/PALF/PLA hybrid composites possess enhanced mechanical, thermal and physical properties with lowered CTE over untreated CF/PALF/PLA hybrid composites. The success of these findings results sustainable and degradable hybrid composites for different outdoor and food packaging-based applications.

Multifunctional bio-based epoxy resin (PEMPAE) was synthesized by reacting Diels-Alder adduct of gum rosin and maleic anhydride (MPA) with pentaerythritol to get the esterified product (PEMPA) which was further epoxidized using epichlorohydrin and potassium hydroxide. This paper includes the synthesis of bio-based imidoamine curing agent (IAEDK) by reacting diamino diphenyl ether (DDE) with dimaleopimaryl ketone (DMPK), a dehydrodecarboxylated derivative of MPA. The synthesized products were characterized by Fourier transform infrared Spectroscopy (FTIR), proton and 13C nuclear magnetic resonance spectroscopy (1H-NMR and 13C-NMR). Curing dynamics of rosin-based epoxy cured with rosinbased imidoamine crosslinker were evaluated using differential scanning calorimetry (DSC) and were compared with resin cured with synthesized DMPK and commercial DDE curing agents. The mechanical properties and thermal stability of the cured epoxy samples were evaluated using a universal testing machine (UTM) and thermogravimetric analyzer (TGA), respectively. The chemical resistance of the samples was determined in terms of % weight loss when immersed in NaOH, HCl and NaCl solutions. The morphological changes were also evaluated via scanning electron microscopy (SEM). Results revealed that rosin-based epoxy cured with imidoamine curing agent gave preeminent properties over the commercial one. The studies suggested that curing properties were greatly affected by the molecular topology and kind of curing agent used.

This study reports on the synthesis of new fluoro functionalized poly(ε-caprolactone)s (F-PCLs) via ring-opening polymerization (ROP) of ε-caprolactone (ε-CL) for different time intervals (24 and 48 h.) by using 2,2,3,3,4,4,5,5-octafluoro-1-pentanol (OFP) as an initiator. The structure and properties of F-PCLs are investigated by Fourier-transform infrared (FT-IR), proton and fluorine 19 nuclear magnetic resonance (1H-NMR and 19F-NMR) spectroscopies, gel permeation chromatography (GPC), energy dispersive scanning electron microscopy (SEM-EDS), atomic force microscopy (AFM), water contact angle (WCA) measurements, thermogravimetric analysis (TGA), and differential scanning calorimetry (DSC). Enzymatic degradation experiments are also conducted to study the biodegradation behavior of terminal F-PCLs. Experimental observations obtained by 1H-NMR, 19F-NMR and GPC indicate that higher reaction time leads to the formation of higher fluorinated repeating units in F-PCLs. This observation is confirmed by results of SEM-EDS, AFM, WCA, DSC and TGA analyses, respectively. Based on the biodegradability study of F-PCLs in degradation solutions in the presence and absence of porcine pancreatic lipase, it can observed that utilization of more extended time in the ROP reaction medium decreases the biodegradation of resulting polymer. With the obtained features, biodegradable F-PCLs might have potential applications, particularly in the fields of drug delivery and tissue engineering, requiring improved thermal but lower wettability properties.

Calcium carbonate nanoparticles of calcite structure and nanometric size were successfully synthesized by mechanochemical processing using low energy mill (100 rpm). Transmission electron micrographs demonstrated that the nanoparticles tend to form agglomerates of approximately 1 µm due to their high surface energy. A study of structure and properties of composite materials resulting from the addition of CaCO3 nanoparticles at concentrations of 1, 2.5 and 5 wt% to epoxy resin was made. Epoxy/1 wt% CaCO3 and epoxy/2.5 wt% CaCO3 composites displayed an increase of 8 and 12°C in glass transition temperature (Tg), respectively. Scanning electron microscopy images of composites revealed a hierarchical structure of micrometric sized extended aggregates of nanometric calcium carbonate particles homogeneously distributed in the polymer matrix. This morphology explains the increase in hydrophobicity, as well as gains in Young’s moduli, which were greater than 59% with respect to the neat epoxy as measured by Nanoindentation. Therefore, this work demonstrates that the optimum range of concentration up to 2.5 wt% of high-quality nano CaCO3 guarantees thermal, mechanical and surface significant improvements associated with a hierarchical microstructure-nanostructure, which ultimately extend the possibilities of application of epoxy materials for nowadays challenges.

A racemic mixture of two stereoregular polylactides (PLAs) (i.e. PLLA and PDLA) allows obtaining wholly amorphous stereocomplex PLA films by solvent casting method. The amorphous phase behavior of stereocomplex PLA is compared with that of PLLA and PDLA by advanced thermal analysis, such as Fast Scanning Calorimetry (FSC) and Dielectric Relaxation Spectroscopy (DRS). FSC allows us to quench at very high cooling rate (up to 4000 K・s–1) the studied polymers and to obtain glassy amorphous phases with high excess of enthalpy. It is shown that stereocomplexation has no influence on the glass transition temperature, the physical aging and on the cooperativity. The α and β processes were examined to study the dielectric properties, such as relaxation time, dielectric strength, and fragility. The results of FSC and DRS are correlated to determine the values of cooperativity length which are found to be similar in a wide temperature range. It is found that the studied polymers have the similar dielectric properties independently on their tacticity.

Novel tough bio-based polyesters poly(ethylene 2,5-thiophenedicarboxylate-co-1,4-cyclohexanedimethylene 2,5-thiophenedicarboxylate)s (PECTFs) were synthesized from 2,5-thiophenedicarboxylic acid (TDCA), 1,4-cyclohexanedimethanol (CHDM) and ethylene glycol (EG). The microstructure, thermal and mechanical properties were investigated. Poly(ethylene 2,5-thiophenedicarboxylate) (PETF) displayed the glass transition temperature (~64 °C) and tensile strength (~72 MPa) similar to poly(ethylene terephthalate) (PET). However, the nonlinear structure of TDCA resulted in an angle of 148° between carboxylic acid carbons and the S atom resulted in a permanent dipole, so the thiophene ring-flipping was hindered and the low elongation at break (~24%) was observed for PETF. The peak corresponding to the secondary relaxation shifted to lower temperature due to the incorporation of CHDM, which yielded ductile copolyesters with high elongation at break. When the CHDM content was equal to or higher than 29%, a high elongation at break (>160%) was observed.

Poly(lactic acid) (PLA) has been found to be important in various applications, such as in the medical, pharmaceutical, and packaging industries. However, the long-term associated degradation process of PLA is a limiting factor for some applications. Therefore, in this research, the influence of corona and radio-frequency (RF) surface plasma treatment on the degradation of PLA in accelerated weathering tests was studied. The accelerated weathering test was applied using standard UV irradiation for up to 2000 h. The morphological/topographical, chemical, crystallization, mechanical, and thermal changes were analyzed after 500, 1000, and 2000 h of accelerated weathering time. The introduction of the polar functional groups caused by plasma treatment on the PLA surface improved its wettability, and therefore, hydrolytic degradation was promoted over the accelerated weathering time. It was revealed that the plasma treatment enhanced the hydrolytic and UV degradation of the PLA, as was confirmed by investigation of the physical, chemical, mechanical, and thermal properties. Moreover, the RF plasma was more pronounced than the corona plasma in the degradation of the PLA. Such an approach represents a pathway to promote and tailor PLA degradation. [ABSTRACT FROM AUTHOR]