Viscoelastic properties and interfacial tension of polystyrene–polyethylene blends

The linear viscoelastic properties of polystyrene polyethylene (PS/PE) blends have been investigated in the molten state. For concentrations of the dispersed phase equal to 30 vol %, the blends exhibited a droplet‐matrix morphology with a volume‐average diameter of 5.5 μm for a 70/30 PS/PE blend at 200 °C and 14.7 μm for a 30/70 PS/PE blend at 230 °C. Enhanced elasticity (G′) for both blends, in the terminal zone, compared to the modulus of the matrix (PS and PE, respectively) was observed. This is related to the deformation of the droplets in the matrix phase and hence to the interfacial forces between the blend components. The results for these uncompatibilized blends are shown to be in agreement with the predictions of the emulsion model of Palierne. These predictions were used to obtain the interfacial tension between PS and PE, which was found to be between 2 and 5 mN/m at 200 °C and 4 ± 1 mN/m at 230 °C. Independent interfacial tension measurements using the breaking‐thread method resulted in a value of 4.7 mN/m and 4.1 mN/m at 200 °C and 230 °C for the respective blends. © 2000 John Wiley & Sons, Inc. J Polym Sci B: Polym Phys 38: 1359–1368, 2000     

Preparation and Characterization of Poly(Lactic Acid)-g-Maleic Anhydride + Starch Blends

Poly(lactic acid) (PLA) and starch copolymers are obtained by reactive blending - varying the starch compositions from 0 to 60%. PLA is functionalized with maleic anhydride (MA), obtaining PLA-g-MA copolymers using dicumyl peroxide as an initiator of grafting in order to improve the compatibility and interfacial adhesion between the constituents. PLA + starch blends without a compatibilizer do not have sufficient interfacial adhesion. Decomposition temperature of PLA is not affected by grafting. Glass transition temperatures and dynamic mechanical properties are affected since MA has a plasticizing effect. Along with an increasing starch content friction decreases while wear loss volume in pin-on-disk tribometry has a minimum at nominal 15% wt. starch but increases at higher starch concentrations. The residual depth in scratching and sliding wear testing has a maximum at 15% starch; there is a minimum of storage modulus E′ determined in dynamic mechanical testing at the same concentration. Microhardness results also reflect the plasticization by MA.     

Transesterification,morphology and some mechanical properties of thermotropic liquid crystal polymers/polycarbonate blends

Blends of polycarbonate (PC) and thermotropic liquid crystal polymer Vectra-A (VA), with up to 20 wt.% VA were prepared at temperatures up to 320°C. Transesterification (TE) was found to take place notably at the highest blending temperature. At this temperature, it increased linearly with the VA content. TE products, located at PC/VA interfaces led to reductions in the size of dispersed phase droplets, as shown by scanning electron microscopy. The inference of increased compatibility was consistent with improvements in mechanical property parameters of the blends. These also showed that mixing time was a factor in defining interfacial states. Acid–base interaction data gave further evidence of the presence of TE products, notably when blending occurred at 320°C, and suggested that ∼10 wt.% of VA was needed to saturate interfaces with PC. The absolute values of acid and base interaction constants were found to be very low, confirming earlier evidence that near 320°C dispersion forces are dominant at PV/VA interfaces, contributing to enhanced compatibility in blends prepared at these high temperatures.     

New approach on the development of plasticized polylactide (PLA): Grafting of poly(ethylene glycol) (PEG) via reactive extrusion

In this work, new ways of plasticizing polylactide (PLA) with low molecular poly(ethylene glycol) (PEG) were developed to improve the ductility of PLA while maintaining the plasticizer content at maximum 20 wt.% PLA. To this end, a reactive blending of anhydride-grafted PLA (MAG-PLA) copolymer with PEG, with chains terminated with hydroxyl groups, was performed. During the melt-processing, a fraction of PEG was grafted into the anhydride-functionalized PLA chains. The role of the grafted fraction was to improve the compatibility between PLA and PEG. Reactive extrusion and melt-blending of neat and modified PLA with PEG did not induce any dramatic drop of PLA molecular weight. The in situ reactive grafting of PEG into the modified PLA in PLA/PEG blends showed a clear effect on the thermal properties of PLA. It was demonstrated by DSC that the mobility gained by PLA chains in the plasticized blends yielded crystallization. The grafting of a fraction of PEG into PLA did not affect this process. However, DSC results obtained after the second heating showed an interesting effect on the T_g when 20 wt.% PEG were melt blended with neat PLA or 10 wt.% MAG-PLA. In the latter case, the T_g displayed by the reactive blend was shifted to even lower temperatures at around 14 °C, while the T_g of neat PLA and PLA blended with 20 wt.% PEG was around 60 and 23 °C, respectively. Regarding viscoelastic and viscoplastic properties, the presence of MAG-PLA does not significantly influence the behavior of plasticized PLA. Indeed, with or without MAG-PLA, elastic modulus and yield stress decrease, while ultimate strain increases with the addition of PEG into PLA.     

环氧基团功能化弹性体增韧聚乳酸的性能

以2种不同结构的弹性体乙烯-辛烯共聚物接枝甲基丙烯酸缩水甘油酯(POE-g-GMA)和乙烯-丙烯酯甲酯-甲基丙烯酯缩水甘油酯三元共聚物(E-MA-GMA)增韧聚乳酸(PLA), 研究了接枝型与嵌段型弹性体的结构对聚乳酸增韧效果的影响. 结果表明, 接枝型聚合物POE-g-GMA与基体PLA之间具有良好的界面相互作用, 当POE-g-GMA的质量分数为15%时, 共混体系的缺口冲击强度为72.4 kJ/m², 而E-MA-GMA的质量分数为15%时, 共混体系的缺口冲击强度为32.4 kJ/m², 结果表明, 接枝型聚合物POE-g-GMA增韧效果明显优于嵌段型E-MA-GMA.     

Thermal,morphological, mechanical and aging properties of polylactide blends with poly(ether urethane) based on chain-extension reaction of poly(ethylene glycol) using diisocyanate

Poly(ether urethane)s(PEU), including PEUI15 and PEUH15, were prepared through chain-extension reaction of poly(ethylene glycol)(PEG-1500) using diisocyanate as a chain extender, including isophorone diisocyanate(IPDI) and hexamethylene diisocyanate(HDI). These PEUs were used to toughen polylactide(PLA) by physical and reactive blending.Thermal, morphological, mechanical and aging properties of the blends were investigated in detail. These PEUs were partially compatible with PLA. The elongation at break of the reactive blends in the presence of triphenyl phosphate(TPP)for PLA with PEUH15 or PEUI15 was much higher than that of the physical blends. The aging test was carried out at-20 °C for 50 h in order to accelerate the crystallization of PEUs. The PEUs in the PLA/PEU blends produced crystallization and formed new phase separation with PLA, resulting in the declined toughness of blends. Fortunately, under the aging condition,although PEUH15 in blends could also form crystallization, the reactive blend of PLA/PEUH15/TPP(80/20/2) had higher toughness than the other blends. The elongation at break of PLA/PEUH15/TPP(80/20/2) dropped to 287% for the aging blend from 350% for the original blend. The tensile strength and modulus of PLA/PEUH15/TPP blend did not change obviously because of the crystallization of PEUH15.     

Rheological Study on Polypropylene/Cycloolefin Copolymer Blends

Summary: Polypropylene, cycloolefin copolymer and their blends were characterized by means of melt flow analysis and capillary rheometry at temperatures between 190 and 230 °C in order to shed more light on COC fiber formation obtained in injection molding process. Melt viscosity and its activation energy as functions of blend composition show negative deviation from the expected additivity (Negative Deviating Blends). The COC/PP viscosity ratio increases with shear rate, but decreases with temperature. High temperature, low viscosity ratio and high shear rate seem to be favorable for fiber formation. Glass transition (from the reversible heat flow curve of modulated DSC) of dumbbell specimens produced by injection molding at 230 °C with COC minor component was 2–4 °C higher than that of grinded pellets obtained from mixing at 190 °C.     

CELLULOSE ACETATE AND EPOXY RESIN BLEND ULTRAFILTRATION MEMBRANES: REPARATION,CHARACTERIZATION, AND APPLICATION

ABSTRACT

Membranes based on cellulose acetate used in ultrafiltration applications lack good, chemical, mechanical and thermal resistance. In order to prepare membranes with improved properties, modification of cellulose acetate with epoxy resin through solution blending was attempted. In the present work, the membrane casting solutions with different polymer blend compositions of cellulose acetate and diglycidyl ether of bisphenol-A (DGEBA) were prepared at 30±2°C. The maximum percent compatibility of the two polymers, cellulose acetate and diglycidyl ether of bisphenol-A, was estimated to be 60/40%. Ultrafiltration blend membranes based on various blend compositions were prepared, characterized in terms of compaction, pure water flux, water content, membrane hydraulic resistance and molecular weight cut-off. The application of these membranes, in rejection of proteins of various molecular weights, are discussed.     

Effect of poly (lactic acid)‐graft‐glycidyl methacrylate as a compatibilizer on properties of poly (lactic acid)/banana fiber biocomposites

The main aim of this study was to synthesis of poly (lactic acid) (PLA)‐graft‐glycidyl methacrylate (GMA) as well as its influence on the properties of PLA/banana fiber biocomposites. PLA‐graft‐GMA graft copolymer (GC) was synthesized by melt blending PLA with GMA using benzoyl peroxide and dicumyl peroxide as initiators. Graft copolymerization was confirmed by FTIR and ¹H‐NMR spectroscopic studies. PLA/silane treated banana fiber (SiB) biocomposites with various GC concentrations were prepared by melt blending followed by injection molding techniques. The influence of GC content on the mechanical, thermal and moisture resistance properties of the composite was investigated. The addition of 15 wt% GC content in the biocomposite provided optimum tensile and flexural strength, which is attributed to the greater compatibility between fiber and PLA matrix. The thermal properties of biocomposites have been evaluated using thermogravimetric analysis which provided evidence of improved interfacial adhesion between SiB and PLA by the addition of GC. Additionally, GC enhanced the moisture absorption resistance of biocomposites. These results indicated that GC is indeed a good candidate as a compatibilizing agent to improve the compatibility in PLA/fiber biocomposites. Copyright © 2015 John Wiley & Sons, Ltd.     

The role of cold crystallization of homochiral crystallites in the superb heat resistant poly(lactic acid)

The superb heat resistance poly(lactic acid) (PLA) were prepared by blending PLA and poly(d ‐lactic acid) (PDLA) with various molecular weight (M_n). Formation of the stereocomplex in the blends was confirmed by differential scanning calorimetry and wide‐angle X‐ray diffraction. The results of the heat resistance implied it is possible that elevating the Vicat penetration temperature of PLA up to 150°C by blending with PDLA. The cold crystallization of homochiral crystallites is proven to be the critical factor affecting the heat resistance of PLA. While the PLA or PLA/PDLA blends were heated to cold crystallization temperature of samples, both the crystal content and the rigid amorphous region content are increased due to the cold crystallization and tethering effect, and the stiffness and heat resistance of the sample are improved. The cold crystallization homochiral crystallites kinetics of PLA and PLA/PDLA blends was also studied. The results showed the activation energy (?E) of cold crystallization increased from 120.30 kJ/mol to 144.66 kJ/mol with the increasing of PDLA content from 2% to 10%.     

Effects of poly(ethylene glycol) on the morphology and properties of biocomposites based on polylactide and cellulose nanofibers

Polylactide (PLA)/cellulose nanofiber (CNF) biocomposites were prepared via solution casting and direct melt mixing. To improve the compatibility, a masterbatch of CNFs and poly(ethylene glycol) (PEG) (1:2) was also prepared. The effects of PEG on the morphology and properties of the biocomposites were investigated. The dispersion/distribution of nanofibers in PLA was improved when the masterbatch was used and the composites were prepared in solution. Substantial effects on the rheological properties of solution-prepared PLA/CNF/PEG composites were observed compared to composites containing no PEG, whereas for melt-prepared composites no significant changes were detected. Increased crystalline content and crystallization temperature were observed for the composites prepared via the masterbatch and solvent casting. The storage modulus of PLA was increased by 42 and 553% at 25 and at 80 °C, respectively, for the solution-based PEG-compatibilized composite containing 2 wt% nanofibers. Also, a better light transmittance was measured for the PLA/CNF/PEG composites prepared in solution.     

Effect of blending ratio and oligomer structure on the thermal transitions of stereocomplexes consisting of a D‐lactic acid oligomer and poly(L‐lactide)

Poly(lactic acid) (PLA) stereocomplexes have high potential as renewable materials for advanced polymer applications, mainly due to their high melting temperature (T_m, typically 230–240°C). The properties of PLA stereocomplexes consisting of linear high molar mass homopolymers have been studied extensively in the past, but the available information about the possibilities to affect the thermal properties of the stereocomplex by varying the structure of the blend components has not been sufficient. Novel stereocomplexes containing linear or star‐shaped D ‐lactic acid (D ‐LA) oligomers and high molar mass poly(L ‐lactide) (L‐ PLA) were thus prepared. The T_m and melting enthalpy (ΔH_m) of the racemic crystallites were found to depend strongly on both the blending ratio and the arm‐length of the D ‐lactic acid oligomer. The preparation method of the oligomers, i.e. step‐growth polymerization or ring‐opening polymerization (ROP), did not affect the T_m or ΔH_m of the blends significantly. Slightly higher ΔH_m values were, however, obtained, when linear oligomers were used. The results thus indicated that the T_m and ΔH_m of PLA stereocomplexes could be optimized, simply by selecting a D ‐LA oligomer having a suitable arm‐length and structure as the other blend component. The possibility to adjust the melting behavior of the stereocomplex blend is a significant advantage and could make PLA suitable for a wider range of products used at elevated temperatures. Copyright © 2010 John Wiley & Sons, Ltd.     

Semicrystalline blends of polyethylene and isotactic polypropylene: Improving mechanical performance by enhancing the interfacial structure

The low‐temperature mechanical behavior of semicrystalline polymer blends is investigated. Isotactic polypropylene (iPP) is blended with both Zeigler–Natta polyethylene (PE) and metallocene PE. Transmission electron microscopy (TEM) on failed tensile bars reveals that the predominate failure mode in the Zeigler–Natta blend is interfacial, while that in the metallocene blend is failure of the iPP matrix. The observed change in failure mode is accompanied by a 40% increase in both tensile toughness and elongation at −10 °C. We argue that crystallite anchoring of interfacially entangled chains is responsible for this dramatic property improvement in the metallocene blend. The interfacial width between PE and iPP melts is approximately 40 Å, allowing significant interfacial entanglement in both blends. TEM micrographs illustrate that the segregation of low molecular weight amorphous material in the Zeigler–Natta blend reduces the number and quality of crystallite anchors as compared with the metallocene blend. The contribution of anchored interfacial structure was further explored by introducing a block copolymer at the PE/iPP interface in the metallocene blend. Small‐angle X‐ray scattering (SAXS) experiments show the block copolymer dilutes the number of crystalline anchors, decoupling the interface. Increasing the interfacial coverage of the block copolymer reduces the number of anchored interfacial chains. At 2% block copolymer loading, the low‐temperature failure mode of the metallocene blend changes from iPP failure to interfacial failure, reducing the blend toughness and elongation to that of the Zeigler–Natta blend. This work demonstrates that anchored interfacial entanglements are a critical factor in designing semicrystalline blends with improved low‐temperature properties. © 2000 John Wiley & Sons, Inc. J Polym Sci B: Polym Phys 38: 108–121, 2000     

聚2,5-呋喃二甲酸乙二醇酯/聚丁二酸丁二醇酯共混物的制备与表征

通过熔融共混制备了聚2,5-呋喃二甲酸乙二醇酯(PEF)/聚丁二酸丁二醇酯(PBS)共混物,探究了制备PEF/PBS共混物的影响因素,考察了共混温度、共混时间、螺杆转速、共混比例对PEF/PBS共混物力学性能的影响因素,并用示差扫描量热仪、热失重、扫描电子显微镜等技术手段对其热性能和相容性进行了表征。 结果表明,当PBS的含量为15%、共混温度为230 ℃,共混时间为90 s、螺杆转速为150 r/min时,为最佳共混制备条件,此时相容性最好,热性能良好,冲击强度和拉伸强度最大,冲击强度相对纯PEF提高了6倍,拉伸强度提高了近20%,从而大幅提高了PEF的冲击强度,有效地增强了PEF的抗冲击韧性。 这些工作为这一生物基聚酯材料的应用提供了可能。     

Study on damping properties of HVBR/EVM blends prepared by in situ polymerization

In comparison with normal damping rubbers such as natural rubber (NR), styrene butadiene rubber (SBR), isobutylene isoprene rubber (IIR) etc., Mo-based high vinyl polybutadiene rubber (HVBR) with high loss factor, excellent aging resistance and glass transition temperature closer to room temperature, is a promising damping material. The effective damping temperature range of HVBR could be further broadened by blending with ethylene-vinyl acetate (EVM) and the effects of blending methods (in situ polymerization blending or mechanical blending) and blending ratios on the damping properties and physical properties of HVBR/EVM blended rubber were studied. HVBR/EVM in situ polymerization blends was prepared by butadiene coordination polymerization by Mo-base catalyst in a toluene solution of EVM. The results of dynamic mechanical analysis (DMA) and scanning electron microscopy (SEM) of the blended vulcanizates via in situ polymerization blending revealed that the compatibility between HVBR and EVM was improved compared with that of the blended vulcanizates via the traditional mechanical blending method. The two phases of HVBR/EVM in situ polymerization blends had good dispersion and uniformity, the damping temperature range was significantly expanded, and the peak and valley of the damping temperature range were greatly improved. A blending ratio of HVBR/EVM900 = 100/40 showed the best damping properties and the effective damping temperature range (tanδ>0.3) was extended from −6.6 °C to 39.4 °C.     

Thermal behaviors and characteristics of polylactide/poly(butylene succinate) blend films via reactive compatibilization and plasticization

Polylactide (PLA)/poly(butylene succinate) (PBS) blend films modified with a compatibilizer and a plasticizer were hot‐melted through a twin screw extruder and prepared by hydraulic press. Toluene diisocyanate (TDI) and polylactide‐grafted‐maleic anhydride (PLA‐g‐MA) were used as compatibilizers, while triethyl citrate and tricresyl phosphate acted as plasticizers. The effects of the type and content of compatibilizer and plasticizer on the mechanical characteristics, thermal properties, crystallization behavior, and phase morphology of the PLA/PBS blend films were investigated. Reactive compatibilization at increasing levels of TDI improved the compatibility of the PLA and PBS, affecting the toughness of the films. As evidenced by scanning electron microscope, the addition of TDI enhanced the interfacial adhesion of the blends, leading to the appearance of many elongated fibrils at the fracture surface. Furthermore, PLA/PBS blending with both TDI and PLA‐g‐MA led to an acceleration of the cold crystallization rate and an increment of the degree of crystallinity ( ). Toluene diisocyanate could be a more effective compatibilizer than PLA‐g‐MA for PLA/PBS blend films. The synergistic combination of compatibilizer and plasticizer brought a significant improvement in elongation at break and tensile‐impact toughness of the PLA/PBS blends, compared with neat PLA. Their failure mode changed from brittle to ductile due to the improved compatibility and molecular segment mobility of the PLA and PBS phases. Differential scanning calorimeter results revealed that the plasticizers triethyl citrate and tricresyl phosphate changed the thermal behavior of T_cc and T_m, affecting α′ and α crystal formations. However, these plasticizers only slightly improved the thermal stability of the films.     

Physical properties and phase separation structure of Antheraea pernyi/Bombyx mori silk fibroin blend films

The physical structure and compatibility of solution-cast Antheraea pernyi/Bombyx mori silk fibroin blend films were stuided by differential scanning calorimetry (DSC), thermomechanical (TMA) and thermogravimetric (TGA) analysis, dynamic viscoelastic measurement, infrared spectroscopy, and x-ray diffractometry. The DSC curves of the blend films showed independent endotherms at 280 and 358°C, corresponding to the thermal decomposition of B. mori and A. pernyi silk fibroins with random coil conformation. The intensity was roughly proportionate to the amount of each component in the blend. The thermal behavior corresponding to the conformational transitions induced by heating on A. pernyi and B. mori silk fibroins overlapped in the temperature range 190–230°C. Thermal expansion and contraction properties, as well as weight retention behavior of the blend films were intermediate between the pure components, as shown by the TMA and TGA curves. The onset temperature of the storage modulus curve decreased markedly, approaching that of B. mori silk fibroin film when the amount of this component in the blend increased. The loss modulus curve of the blend films showed two peaks at ca. 190 and 210°C, the former corresponding to B. mori, and the latter to A. pernyi silk fibroin. Infrared spectra of the blends exhibited absorption bands characteristic of the pure components overlapping in the spectral region 2000–400 cm^?1. The x-ray diffraction peaks at 23 and 21.5°, attributed to the crystalline spacings of A. pernyi and B. mori fibroins, respectively, overlapped in the diffraction curves of the blends, while the peak at 11.4°, of A. pernyi, increased as the content of this fibroin in the blend increased. The degree of crystallinity, calculated from the x-ray diffraction curves, diminished as the amount of B. mori silk fibroin decreased. A low degree of compatibility exists between the two fibroins when they are cast from aqueous solution in the experimental conditions adopted in this work. © 1994 John Wiley & Sons, Inc.     

Rheo-optical FT-IR spectroscopy of poly(3-hydroxybutyrate)/poly(lactic acid) blend films

The orientation of poly(3-hydroxybutyrate) (PHB) and poly(lactic acid) (PLA) segments in PHB/PLA blend films cast from chloroform solutions with compositions PHB < PLA was studied during uniaxial elongation up to 250% strain at 50 °C by in-situ rheo-optical FT-IR spectroscopy. From the orientation functions of the ν(CO) bands of the blend components, it was derived that the PLA chains orient in the direction of elongation while the PHB chains orient perpendicular to the drawing direction. PHB homopolymer and PHB/PLA blend films with PHB > PLA compositions could only be oriented by cold drawing in ice water after quenching from the melt. The IR-dichroic effects of films drawn under these conditions indicate for both blend components a chain alignment parallel to the drawing direction.     

Reactive blending toughened PLA by in situ formation of polyurethane crosslinked elastomer

Polylactide (PLA)/polyurethane (PU) composites were prepared by reactive blending method with in-situ formation of PU particles via the reaction between polyester polyol (PPG) and toluene-2,4-diisocyanate (TDI). The interfacial compatibility and adhesion between the PLA and PU phases were greatly improved by the reaction of the terminal hydroxyl groups of PLA and N=C=O groups of TDI forming graft copolymer, as confirmed by FTIR spectroscopy. The elongation at break and notch impact strength of PLA/PU composites increased considerably with increasing PU content, and the tensile strength of PLA/PU composites decreased slightly compared with that of pure PLA. The excellent interfacial adhesion, dispersed PU elastomeric particles acting as stress concentration areas and the triggering of large matrix shearing yielding and many fibrils by internal cavitation were the main mechanical toughening mechanisms.     

The relationship between the compatibility and thermodegradation stability of modified polyetherimide/bismaleimide resins by hyperbranched polysiloxane with high degree of branching

Amino‐terminated hyperbranched polysiloxane (AHBSi) with high degree of branching (0.8) is used to improve the compatibilization of polyetherimide (PEI)/allyl bisphenol A modified bismaleimide (BD) blend. The relationship between the compatibility and thermal/thermal‐oxidative stability of the AHBSi/PEI/BD system is intensively investigated. Although PEI has high thermal stability, the PEI/BD blend has poorer thermal stability than BD resin due to the incompatibility. With the addition of AHBSi into the PEI/BD blend, AHBSi chemically connects PEI and BD, leading to the increased compatibility; moreover, interestingly, both thermal and thermo‐oxidative stabilities are significantly improved. Under a N₂ atmosphere, the addition of 0.5 wt% of AHBSi increases the initial degradation temperature of the PEI/BD blend from 395°C to 412°C. The thermodegradation kinetics were studied, and results show that the AHBSi/PEI/BD system has much higher activation energy of degradation in both N₂ and air atmospheres. The origin behind these interesting results is intensively investigated. Copyright © 2013 John Wiley & Sons, Ltd.