Foaming behavior of polypropylene/polystyrene blends enhanced by improved interfacial compatibility

A series of polypropylene (PP)/polystyrene (PS) blends were prepared by solvent blending with PS‐grafted PP copolymers (PP‐g‐PS) having different PS graft chain length as compatibilizers. The interfacial compatibility was significantly improved with increasing PS graft chain length until the interface was saturated at PS graft chain length being 3.29 × 10³ g/mol. The blends were foamed by using pressure‐quenching process and supercritical CO₂ as the blowing agent. The cell preferentially formed at compatibilized interface because of low energy barrier for nucleation. Combining with the increased interfacial area, the compatibilized interface lead to the foams with increased cell density compared to the uncompatibilized one. The increase in interfacial compatibility also decreased the escape of gas, held more gas for cell growth, and facilitated the increase in expansion ratio of PP/PS blend foams. © 2008 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 46: 1641–1651, 2008     

In situ preparation of cross‐linked polystyrene/poly(methyl methacrylate) blend foams with a bimodal cellular structure

In situ preparation of a cross‐linked poly(methyl methacrylate) (PMMA) and polystyrene (PS) blend and its foaming were investigated for creating a bimodal cellular structure in the foam. Methyl methacrylate (MMA) monomer was dissolved in PS under supercritical CO₂ at a temperature of 60 °C and a pressure of 8 MPa, and the polymerization of MMA was conducted at 100 °C and 8 MPa CO₂, with a cross‐linking agent in PS. The blend was successively foamed by depressurizing the CO₂. CO₂ played the roles of plasticizing the PS and enhancing the monomer dispersion in PS during the sorption process and as a physical blowing agent in the foaming process. The cross‐linking agent was used for controlling the elasticity of polymerized PMMA domains and differentiating their elasticity from that of the PS matrix. The difference in elasticity delayed the bubble nucleation in the PMMA domains from that in the PS and made the cell size bimodal distribution, in which the smaller cells ranging from 10 to 30 µm in diameter were located in the wall of large cells of 200–400 µm in diameter. The effects of the initial MMA content, the concentration of cross‐linking agent, and the depressurization rate on the bimodal cell structure and bulk foam density were investigated. Copyright © 2011 John Wiley & Sons, Ltd.     

Preparation and characterization of microcellular polystyrene/polystyrene ionomer blends with supercritical carbon dioxide

The preparation of microcellular polystyrene (PS), lightly sulfonated polystyrene (SPS), zinc‐neutralized lightly sulfonated polystyrene (ZnSPS), and blends of PS/SPS and PS/ZnSPS via supercritical CO₂ was carried out with the pressure‐quench process. Both higher foaming temperature and lower pressure result in larger cell sizes, lower cell densities, and lower relative density for microcellular ionomers and blends as for microcellular PS. The difference among various microcellular samples is the change of cell size with the sample composition. The cell size decreases in the sequence from SPS, through PS/SPS blends, PS and PS/ZnSPS blends, to ZnSPS. The diffusivity of CO₂ in samples also decreases in the sequence from SPS, through PS/SPS blends, PS and PS/ZnSPS blends, to ZnSPS. For this series of samples with similar structure and identical solubility of CO₂, the varying diffusivity is responsible for the difference of cell sizes. © 2003 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 41: 368–377, 2003     

Microcellular foaming of polylactide and poly(butylene adipate‐co‐terphathalate) blends and their CaCO3 reinforced nanocomposites using supercritical carbon dioxide

Foamed polylactide (PLA), PLA–PBAT (poly (butylene adipate‐co‐terphathalate)) blend and their composites with CaCO₃ were prepared in a batch process using supercritical carbon dioxide (CO₂) at 12 MPa and 45°C. The solubility of CO₂ and its diffusion patterns in different PLA samples was investigated. PLA systems had a relatively high CO₂ solubility related to the carboxyl groups. CO₂ desorption behaviors in PLA systems first followed the Fickian diffusion mechanism in short time and then decreased slowly to a plateau. The addition of both PBAT and CaCO₃ into PLA impeded the desorption of CO₂. In the presence of second phase PBAT, nanoparticles CaCO₃ and dissolved CO₂, the PLA crystallization behavior investigated by DSC technique was greatly changed. As the desorption time increased, the gas induced crystallinity slightly decreased in consequence of less CO₂ content in each system and thus less plasticization effect. The cell morphology of foamed PLA and PLA composites showed interesting microstructure patterns. The prepared pure PLA foam exhibits a typical bimodal structure because of the foaming in both the amorphous and crystalline zones. With PBAT and CaCO₃ into PLA, the composite foam presented significant increase in cell uniformity and cell density. With less CO₂ content in each PLA sample, the cell structure showed interesting variation. Pure PLA foam presented transition from bimodal structure to more uniform cell structure with decreased cell density. In contract, PLA–PBAT foam show unfoamed regions because of none CO₂ left in the separated PBAT phase. Copyright © 2016 John Wiley & Sons, Ltd.     

Compatibilization efficiency of styrene–butadiene multiblock copolymers in PS/PP blends

The compatibilizing effect of di‐, tri‐, penta‐, and heptablock (two types) copolymers with styrene and butadiene blocks was studied in polystyrene/polypropylene (PS/PP) 4/1 blends. The structure of PS/PP blends with the addition of 5 or 10 wt % of a block copolymer (BC) was determined on several scale levels by means of transmission electron microscopy (TEM) and small‐angle X‐ray scattering (SAXS). The results of the structure analysis were correlated with measured stress‐transfer properties: elongation at break, impact, and tensile strength. Despite the fact that the molar mass of the PS blocks in all the BCs used was about 10,000, that is, below the critical value M^* (～18,000) necessary for the formation of entanglements of PS chains, all the BCs used were found to be good compatibilizers. According to TEM, a certain amount of a BC is localized at the interface in all the analyzed samples, and this results in a finer dispersion of the PP particles in the PS matrix, the effect being more pronounced with S‐B‐S triblock and S‐B‐S‐B‐S pentablock copolymers. The addition of these two BCs to the PS/PP blend also has the most pronounced effect on the improvement of mechanical properties of these blends. Hence, these two BCs can be assumed to be better compatibilizers for the PS/PP (4/1) blend than the S‐B diblock as well as both S‐B‐S‐B‐S‐B‐S and B‐S‐B‐S‐B‐S‐B heptablock copolymers. In both types of PS/PP/BC blends (5 or 10 wt % BC), the BC added was distributed between both the PS/PP interface and the PS phase, and, according to SAXS, it maintained a more or less ordered supermolecular structure of neat BCs. © 2001 John Wiley & Sons, Inc. J Polym Sci B: Polym Phys 39: 931–942, 2001     

Understanding Behavior of Polycaprolactone–Gelatin Blends under High Pressure CO<Subscript>2</Subscript>

Polycaprolactone (PCL) is widely used in biomedical applications as electrospun fibers or porous foams. As PCL is synthetic polymer, many researchers have explored blends of PCL–gelatin to combine mechanical and bioactive properties of individual components. High pressure carbon dioxide (CO2) has been studied to foam and impregnate many biocompatible polymers. In case of PCL–gelatin blends, certain compositions can be swelled reversibly under high pressure CO₂ without permanent deformation. This allows successful impregnation of PCL–gelatin blends under CO₂. This study summarizes effect of different treatments adopted during impregnation process including high pressure CO2 on several blend compositions of PCL–gelatin blends. Stress relaxation, polymer melting and dissolution were observed during several treatments which affects porosity and scaffold structure significantly. Results summarized in this study will aid in optimum selection of PCL–gelatin blend composition for biomedical applications. Furthermore, CO₂ solubility in polymers is restricted due to thermodynamic limitations but can be altered in the presence of a co-solvent to produce better foams. PCL can be foamed using supercritical CO₂. However, CO₂ foaming of PCL–gelatin blend becomes challenging to simultaneous swelling of PCL and compression of gelatin providing blend structural stability. This study has demonstrated ability of supercritical CO₂ to foam PCL–gelatin blends in presence of water to create porous structure. These foams were subjected post-fabrication crosslinking and supercritical CO₂ without losing porosity of foams. Thus, creating a strategy to use environmentally benign processes to fabricate, crosslink and impregnate porous scaffolds for biomedical applications.     

聚乙烯-g-聚苯乙烯对线性低密度聚乙烯/聚苯乙烯共混物机械性能和发泡行为的影响

以通过开环易位聚合、加氢反应和原子转移自由基聚合技术结合制备的聚乙烯-g-聚苯乙烯(PE-g-PS)作为增容剂,研究了加入不同PS支链长度的PE-g-PS对于线性低密度聚乙烯/聚苯乙烯(LLDPE/PS)共混物的机械性能和发泡行为的影响。 以典型组成m(LLDPE):m(PS)=70:30共混物为例,考察了PE-g-PS对共混物拉伸性能的影响。 相对于二元共混物,增容剂的加入使得断裂伸长率、拉伸强度和屈服强度皆提高,且含长PS支链的增容体系提高更明显。 采用超临界CO₂釜式发泡工艺,考察了PE-g-PS中PS支链长度对共混物发泡行为的影响。 结果表明,相对于短PS支链体系,加入PE-g-PS_1.59k(PS相对分子质量为1590)后的泡孔结构更加均一,完全没有“缝隙”形貌的出现。 当发泡温度降至80 ℃时,即使存在LLDPE发泡空间限制作用(LLDPE无法发泡),加入支链长度更长的PE-g-PS_1.59k后泡孔分布也更加均一。     

Effect of nano‐polystyrene (nPS) on thermal,rheological, and mechanical properties of polypropylene (PP)

Polystyrene nanoparticles (nPS) in the range of 10–100 nm with spherical shape were synthesized by oil/water (o/w) microemulsion process. In this process ammonium persulfate (APS) as an initiator, sodium dodecyl sulphate as a surfactant and n‐pentanol as cosurfactant were used. Isolated nPS was characterized by FTIR and ¹H NMR spectroscopy. DSC studies of nPS showed higher T_g as compared to bulk PS. The effect of lower weight percentage (wt%) of nPS on the mechanical, rheological, and thermal properties of PP was investigated. The blends were prepared individually on brabender plastograph by incorporating nPS of ～60 nm with different wt% of loading (i.e., 0.10–0.5%). It was shown from the experimental results that thermal, rheological, and mechanical properties were increased as the polymer particles blended with PP. Blends with 0.25 wt% loading of nPS exhibit better properties compared with that of other wt% loadings. The improvements in properties were due to the close packing of PP chains as recorded by improvement in crystallinity of PP with the addition of nPS as shown by SEM. Copyright © 2010 John Wiley & Sons, Ltd.     

Effect of PEO‐PPO‐PEO copolymer on the mechanical and thermal properties and morphological behavior of biodegradable poly (L‐lactic acid) (PLLA) and poly (butylene succinate‐co‐L‐lactate) (PBSL) blends

A blend of two biodegradable and semi‐crystalline polymers, poly (L‐lactic acid) (PLLA; 70 wt%) and poly (butylene succinate‐co‐L‐lactate) (PBSL; 30 wt%), was prepared in the presence of various polyethylene oxide‐polypropylene oxide‐polyethylene oxide (PEO‐PPO‐PEO) triblock copolymer contents (0.5, 1, 2 wt%). Mechanical, thermal properties, and Fourier transform infrared (FTIR) analysis of the blends were investigated. It was found that the addition of copolymer to PLLA/PBSL improved the fracture toughness of the blends as shown by mode I fracture energies. It was supported by morphological analysis where the brittle deformation behavior of PLLA changed to ductile deformation with the presence of elongated fibril structure in the blend with copolymer system. The glass transition temperature (T_g), melting temperature (T_m) of PLLA, and PBSL shift‐closed together indicated that some compatibility exists in the blends. In short, PEO‐PPO‐PEO could be used as compatibilizer to improve the toughness and compatibility of the PLLA/PBSL blends. Copyright © 2010 John Wiley & Sons, Ltd.     

Synthesis and characterization of polyethylene‐g‐polystyrene as the compatibilizer for polypropylene/ Polystyrene blends

Polyethylene‐g‐polystyrene (PE‐g‐PS) was synthesized as a compatibilizer for polypropylene/polystyrene­(PP/PS) blends by the living radical polymerization of styrene with polyethylene‐co‐glycidylmethacrylate (PE‐co‐GMA). The compatibilizer effect of PE‐g‐PS on the morphology and thermal properties of PP/PS blends was investigated. The crystalline temperature of PP in PP/PS blends decreased with increasing PE‐g‐PS contents. Morphologies of PP/PE‐g‐PS/PS blends showed much better dispersion of each domain for higher PE‐g‐PS contents. The molecular weight of PS segment in PP/PE‐g‐PS/PS blend was increased by addition of styrene monomer during the post melt blending process where post living radical polymerization reaction proceeded. Copyright © 2003 John Wiley & Sons, Ltd.     

Influence of extender oil composition on flowing property,thermal stability,and morphology of styrene‐b‐ethylene‐co‐butylene‐b‐styrene copolymer/polypropylene/oil blends

In this study, a series of styrene‐b‐ethylene‐co‐butylene‐b‐styrene copolymer (SEBS)/polypropylene (PP)/oil blends with different kinds of oil composition was developed through melt blending. The effect of oil with different composition and properties on its phase equilibrium and “redistribution” in multiphasic SEBS elastomer was systematically studied for the first time. Moreover, an integral influencing mechanism of oil composition on the structure and properties of SEBS/PP/oil blends was also put forward. The mineral oil was mainly distributed in ethylene/butylene (EB)/PP phase, which greatly enhanced the processing flowability of SEBS/PP/oil blends. With increasing oil C_N content, a redistribution of oil appeared and excess naphthenic oil (NO) entered the interphase of soft and hard phases. The dynamic mechanical thermal analysis (DMTA) analysis indicated that the polystyrene (PS) phase was plasticized, which also helped to improve the processing fluidity of blends. However, the plasticizing of physical cross‐linking point PS resulted in a decrease in mechanical strength and thermal stability. Small‐angle X‐ray scattering (SAXS) and transmission electron microscope (TEM) results showed that PS phase (45 nm to 55 nm) cylindrically distributed in EB/PP/oil matrix, the excess NO in the interphase enlarged the distance between PS phase and widen the escape channel for oil migration. At over 45% oil C_N content, the electron density difference between soft and hard phases reduced to the minimum, same as T_gPS, indicating a deeper plasticizing effect. The PS phase swelled and exhibited elastic behavior; thus, the force could be uniformly transferred between two phases. Importantly, a recover in strength and thermal stability was observed in O‐5 blend. This work significantly filled the gap of studies in oil‐extended thermoplastic elastomers (TPEs), exhibiting great theoretical guiding significance and application value.     

Effects of polystyrene‐b‐poly(ethylene/propylene)‐b‐polystyrene compatibilizer on the recycled polypropylene and recycled high‐impact polystyrene blends

The recycled polypropylene/recycled high‐impact polystyrene (R‐PP/R‐HIPS) blends were melt extruded by twin‐screw extruder and produced by injection molding machine. The effects of polystyrene‐b‐poly(ethylene/propylene)‐b‐polystyrene copolymer (SEPS) used as compatibilizer on the mechanical properties, morphology, melt flow index, equilibrium torque, and glass transition temperature (T_g) of the blends were investigated. It was found that the notch impact strength and the elongation at break of the R‐PP/R‐HIPS blends with the addition of 10 wt% SEPS were 6.46 kJ/m² and 31.96%, which were significantly improved by 162.46% and 57.06%, respectively, than that of the uncompatibilized blends. Moreover, the addition of SEPS had a negligible effect on the tensile strength of the R‐PP/R‐HIPS blends. Additionally, the morphology of the blends demonstrated improved distribution and decreased size of the dispersed R‐HIPS phase with increasing the SEPS content. The increase of the melt flow index and the equilibrium torque indicated that the viscosity of the blends increased when the SEPS was incorporated into the R‐PP/R‐HIPS blends. The dynamic mechanical properties test showed that when the content of SEPS was 10 wt%, the difference of T_g decreased from 91.72°C to 81.51°C. The results obtained by differential scanning calorimetry were similar to those measured by dynamic mechanical properties, indicating an improved compatibility of the blends with the addition of SEPS.     

Uncross‐linked polypropylene (PP)/ethylene‐propylene‐diene (EPDM)/multi walled carbon nanotube (MWCNT) and dynamically vulcanized PP/EPDM/MWCNT nanocomposites

In this study, relatively large amounts of polypropylene (PP), ethylene‐propylene‐diene (EPDM), and multi‐walled carbon nanotube (MWCNT) were melt‐mixed with and without DCP. Dynamically vulcanized PP/EPDM (TPV)/MWCNT nanocomposites were prepared by two methods: the MWCNTs were added either before or after the dynamic vulcanization of the blends. The effects of composition, rotor speed, and dynamic vulcanization on their surface resistivity were investigated. The surface resistivity of uncross‐linked PP/EPDM/MWCNT nanocomposites increases with increasing the content of EPDM. At PP/EPDM (70/30 wt%) nanocomposite with 1.5 phr MWCNT, slightly lower surface resistivity is obtained by increasing the rotor speed during mixing. However, for PP/EPDM (50/50 wt%) and PP/EPDM (30/70 wt%) nanocomposites, surface resistivity decreases with increasing the rotor speed from 30 to 60 rpm. But further increase in rotor speed (90 rpm) leads to an increase of surface resistivity. When the MWCNTs were added after the dynamic vulcanization of the blends, the surface resistivity of TPV70/MWCNTnanocomposite is lower than that of uncross‐linked PP/EPDM/MWCNT nanocomposite. However, when the MWCNTs were added before the dynamic vulcanization of the blends, the surface resistivity of TPV70/MWCNT nanocomposite is >10¹² Ω/square. Copyright © 2010 John Wiley & Sons, Ltd.     

Correlation of Morphology Evolution with Superior Mechanical Properties in PA6/PS/PP/SEBS Blends Compatibilized by Multi-phase Compatibilizers

In this study,the maleic anhydride(MAH)and styrene(St)dual monomers grafted polypropylene(PP)and poly[styrene-b-(ethylene-co-butylene)-b-styrene](SEBS),i.e.PP-g-(MAH-co-St)and SEBS-g-(MAH-co-St)are prepared as multi-phase compatibilizers and used to compatibilize the PA6/PS/PP/SEBS(70/10/10/10)model quaternary blends.Both PS and SEBS are encapsulated by the hard shell of PP-g-(MAH-co-St)in the dispersed domains(about 2μm)of the PA6/PS/PP-g-(MAH-co-St)/SEBS(70/10/10/10)quaternary blend.In contrast,inside the dispersed domains(about 1μm)of the PA6/PS/PP/SEBS-g-(MAH-co-St)(70/10/10/10)quaternary blend,the soft SEBS-g-(MAH-co-St)encapsulates both the hard PS and PP phases and separates them.With increasing the content of the compatibilizers equally,the morphology of the PA6/PS/(PP+PP-g-(MAH-co-St))/(SEBS+SEBS-g-(MAH-co-St))(70/10/10/10)quaternary blends evolves from the soft(SEBS+SEBS-g-(MAH-co-St))encapsulating PS and partially encapsulating PP(about 1μm),then to PS exclusively encapsulated by the soft SEBS-g-(MAH-co-St)and then separated by PP-g-(MAH-co-St)inside the smaller domains(about 0.6μm).This morphology evolution has been well predicted by spreading coefficients and explained by the reaction between the matrix PA6 and the compatibilizers.The quaternary blends compatibilized by more compatibilizers exhibit stronger hierarchical interfacial adhesions and smaller dispersed domain,which results in the further improved mechanical properties.Compared to the uncompatibilized blend,the blend with both 10 wt%PP-g-(MAH-co-St)and 10 wt%SEBS-g-(MAH-co-St)has the best mechanical properties with the stress at break,strain at break and impact failure energy improved significantly by 97%,71%and 261%,respectively.There is a strong correlation between the structure and property in the blends.     

Compatibilizing effect of functionalized polystyrene blends: a study of morphology,thermal, and mechanical properties

Polystyrene (PS), being an amorphous polymer is immiscible with other polymers. To engender miscible blends, PS has been functionalized with an active amino‐functional group on the molecular chains of PS to yield amino‐substituted polystyrene (APS), which serves as a reactive compatibilizer. The compatibilization effect of amino functionalized polystyrene on the rubber toughening was explored and results were compared in terms of morphology, thermal, and mechanical properties of PS/SEBS‐g‐MA versus APS/SEBS‐g‐MA blends. In addition, the effect of rubber content on the blend morphology and mechanical properties were investigated. An appreciable change in the thermal stability of APS blends in comparison with PS blend has been probed. A marked correlation has been observed between phase morphology and thermal stability. Use of APS produced the compatibilized blends which render improved blend morphology, enhanced thermal and mechanical properties. Optimal thermal, morphological and mechanical profiles were depicted by 20‐wt% APS blend. Copyright © 2008 John Wiley & Sons, Ltd.     

The influence of CaCO3 filler component on thermal decomposition process of PP/LDPE/DAP ternary blend

Polypropylene‐low density polyethylene (PP‐LDPE) blends involving PP‐LDPE (90/10 wt%.) with (0.06 wt%) dialkyl peroxide (DAP) and different amounts (5, 10, 20 wt%) of calcium carbonate (CaCO₃) were prepared by melt‐blending with a single‐screw extruder. The effect of addition of CaCO₃ on thermal decomposition process and kinetic parameters, such as activation energy and pre‐exponential factor of PP‐LDPE blend with DAP matrix, was studied. The kinetics of the thermal degradation of composites was investigated by thermogravimetric analysis in dynamic nitrogen atmosphere at different heating rates. TG curves showed that the thermal decomposition of composites occurred in one weight‐loss stage. The apparent activation energies of thermal decomposition for composites, as determined by the Tang method (TM), the Kissinger–Akahira–Sunose method (KAS), the Flynn–Wall–Ozawa method (FWO), and the Coats–Redfern (CR) method were 156.6, 156.0, 159.8, and 167.7 kJ.mol^?1 for the thermal decomposition of composite with 5 wt% CaCO₃, 191.5, 190.8, 193.1, and 196.8 kJ.mol^?1 for the thermal decomposition of composite with 10 wt% CaCO₃, and 206.3, 206.1, 207.5, and 203.8 kJ mol^?1 for the thermal decomposition of composite with 20 wt% CaCO₃, respectively. The most likely decomposition process for weight‐loss stages of composites with CaCO₃ content 5 and 10 wt% was an A_n sigmoidal type. However, the most likely decomposition process for composite with CaCO₃ content 20 wt% was an R_n contracted geometry shape type in terms of the CR and master plots results. It was also found that the thermal stability, activation energy, and thermal decomposition process were changed with the increase in the CaCO₃ filler weight in composite structure. Copyright © 2009 John Wiley & Sons, Ltd.     

Molecular weight dependence of polystyrene segmental dynamics in dilute blends with poly(vinyl methyl ether)

The segmental dynamics of backbone‐deuterated polystyrenes (d₃PS) with varying molecular weights (1.7–67 kg/mol) have been measured in blends with poly(vinyl methyl ether) (PVME). ²H NMR T₁ values at 15 and 77 MHz are reported for the pure d₃PS and for the dilute d₃PS component in PVME matrices. The temperature shift that is needed to superpose the NMR T₁ data for the pure d₃PS and the d₃PS as a dilute component in the blend ranges from 45 to 70 K. In the framework of Lodge/McLeish model, the self‐concentration value for d₃PS in these dilute blends with PVME is found to be independent of molecular weight. We thus establish for this system that the substantial influence of molecular weight on the blend segmental dynamics can be explained by homopolymer T_g differences. © 2007 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 45: 2252–2262, 2007     

Tailoring of interface of polypropylene/polystyrene/carbon nanofibre composites by polystyrene-block-poly(ethylene-ran-butylene)-block-polystyrene

Mechanical and physical properties of polypropylene (PP)/polystyrene (PS) blend, PP/PS/polystyrene-block-poly(ethylene-ran-butylene)-block-polystyrene (SEBS) ternary blend and their composites with carbon nanofibers (CNF) were investigated. Composites of ternary blend exhibited superior properties compared to those of binary blends. Mechanical performance of nanocomposites was intimately related to their phase morphology. PP/PS/SEBS/0.1 wt% CNF hybrid composites exhibited excellent impact strength (Four-fold increase compared to PP/PS blend) and ductility (12-fold increase in elongation at break, with respect to PP/PS blend). Moreover, these composites displayed good tensile strength and modulus (15% increase in Young's modulus, compared to PP/PS/SEBS blend) and are suitable for various end-use applications including automobile applications. Although crystallinity of PP phase is decreased by the incorporation of CNF, thermal stability of the composites remained almost unaffected. Contact angle measurements revealed that ternary composites exhibited maximum hydrophobicity.     

Mechanical properties of polypropylene (PP) + high‐density polyethylene (HDPE) binary blends: Non‐isothermal degradation kinetics of PP + HDPE (80/20) Blends

In this study, the mechanical properties and non‐isothermal degradation kinetics of polypropylene (PP), high‐density polyethylene (HDPE) with dilauroyl peroxide and their blends in different mixture ratios were investigated. The effects of adding dilauroyl peroxide (0–0.20 wt%) on the mechanical and thermal properties of PP + HDPE blends have been studied. On the other hand, the kinetics of the thermal degradation and thermal oxidative degradation of PP + HDPE (80/20 wt%) blends were studied in different atmospheres, to analyze their thermal stability. The kinetic and thermodynamic parameters such as the activation energy, E_a, the pre‐exponential factor, A, the reaction order, n, the entropy change, the enthalpy change, and the free energies of activated complex related to PP, HDPE, and blend systems were calculated by means of the several methods on the basis of the single heating rate. A computer program was developed for automatically processing the data to estimate the reaction parameters by using different models. Most appropriate method was determined for each decomposition step according to the least‐squares linear regression. Copyright © 2013 John Wiley & Sons, Ltd.     

Morphology,structure, and properties of in situ compatibilized linear low‐density polyethylene/polystyrene and linear low‐density polyethylene/high‐impact polystyrene blends

Blends of linear low‐density polyethylene (LLDPE) with polystyrene (PS) and blends of LLDPE with high‐impact polystyrene (HIPS) were prepared through a reactive extrusion method. For increased compatibility of the two blending components, a Lewis acid catalyst, aluminum chloride (AlCl₃), was adopted to initiate the Friedel–Crafts alkylation reaction between the blending components. Spectra data from Raman spectra of the LLDPE/PS/AlCl₃ blends extracted with tetrahydrofuran verified that LLDPE segments were grafted to the para position of the benzene rings of PS, and this confirmed the graft structure of the Friedel–Crafts reaction between the polyolefin and PS. Because the in situ generated LLDPE‐g‐PS and LLDPE‐g‐HIPS copolymers acted as compatibilizers in the relative blending systems, the mechanical properties of the LLDPE/PS and LLDPE/HIPS blending systems were greatly improved. For example, after compatibilization, the Izod impact strength of an LLDPE/PS blend (80/20 w/w) was increased from 88.5 to 401.6 J/m, and its elongation at break increased from 370 to 790%. For an LLDPE/HIPS (60/40 w/w) blend, its Charpy impact strength was increased from 284.2 to 495.8 kJ/m². Scanning electron microscopy micrographs showed that the size of the domains decreased from 4–5 to less than 1 μm, depending on the content of added AlCl₃. The crystallization behavior of the LLDPE/PS blend was investigated with differential scanning calorimetry. Fractionated crystallization phenomena were noticed because of the reduction in the size of the LLDPE droplets. The melt‐flow rate of the blending system depended on the competition of the grafting reaction of LLDPE with PS and the degradation of the blending components. The degradation of PS only happened during the alkylation reaction between LLDPE and PS. Gel permeation chromatography showed that the alkylation reaction increased the molecular weight of the blend polymer. The low molecular weight part disappeared with reactive blending. © 2003 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 41: 1837–1849, 2003