Phase separation of off‐critical polymer blends of poly(styrene‐co‐maleic anhydride) and poly(methyl methacrylate). II. Morphology and mechanical properties

The effects of the phase‐separation temperature and time on the mechanical properties and morphology of poly(methyl methacrylate)/poly(styrene‐co‐maleic anhydride with 10 wt% ethyl acrylate) (SMA) blends were studied. Two compositions (20/80 and 40/60 w/w SMA/PMMAe) were prepared with a miniature twin‐screw extruder. Compared with those of the miscible blends, the Young's modulus values of the blends increased after the phase separation of the 40/60 SMA/PMMAe blend and within the early stage of spinodal decomposition of the 20/80 SMA/PMMAe blend. The mechanical properties, in terms of the tensile strength at break and the elongation, were better for the miscible blends than for the phase‐separation blends. This was believed to be the result of changes in the composition and molecular reorganization. The changes in the phase‐separating domains of both compositions, as observed by transmission electron microscopy, had no significant influence on the tensile moduli. Detailed studies of the morphology revealed a cocontinuous structure, indicating that the blends underwent spinodal decomposition. A morphological comparison of the two compositions illustrated the validity of the level rule. The growth rate of the droplet size was determined by approximation from the light scattering data and by direct measurements with transmission electron microscopy. The discrepancies observed in the droplet size growth rate were attributed to heat variations induced by the different sample thicknesses and heat transfer during the investigation. © 2004 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 42: 886–897, 2004     

Melt‐processable blends of ionic poly(p‐phenylene terephthalamide) and poly(4‐vinylpyridine): Relaxation behavior

Melt‐processable blends were prepared from rigid molecules of an ionically modified poly(p‐phenylene terephthalamide) (PPTA) and flexible‐coil molecules of poly(4‐vinylpyridine) (PVP). Dynamic mechanical analyses of blends with 50% or more of the ionic PPTA component revealed the presence of two distinct phases. The glass‐transition temperature of the more stable, ionic PPTA‐rich phase increased linearly with the ionic PPTA content. The second phase present in these blends was an ionic PPTA‐poor, or a PVP‐rich, phase. For this phase, a reasonably good fit of the data, showing the glass‐transition temperature as a function of the ionic PPTA content, was achieved between the results of this study and the reported results of previous investigation of molecular composites of the same two components with ionic PPTA contents of 15 wt % or less. The possible influence of annealing on the blend structure of a 90/10 blend of ionic PPTA and PVP was examined. © 2003 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 41: 1468–1475, 2003     

Improving polyethylene–octene elastomer/chitosan by graftation of acrylic acid onto polyethylene–octene elastomer—mechanical properties and biodegradability examination and composites characterization

In this study, the properties of polyethylene–octene elastomer/chitosan (POE/chitosan) and acrylic acid (AA)‐grafted‐polyethylene–octene elastomer/chitosan (POE‐g‐AA/chitosan) were examined using various characterizing instruments. Mechanical and thermal properties of POE deteriorated noticeably when it was blended with chitosan, due to the unsatisfactory compatibility between the two phases. The greater compatibility of POE‐g‐AA with chitosan, due to the formation of ester carbonyl and imide groups, led to a much better dispersion and homogeneity of chitosan in the POE‐g‐AA matrix and consequently to noticeably better mechanical properties. Furthermore, with a lower melting point temperature, the POE‐g‐AA/chitosan blend was more easily processed than POE/chitosan. POE‐g‐AA/chitosan had a higher water resistance than POE/chitosan. Both blends suffered weight loss when buried in soil, especially at high levels of chitosan substitution, indicating that both were biodegradable. The mechanical properties of both blends, such as tensile strength and elongation at break, also deteriorated after being buried in soil. © 2003 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 41: 3882–3891, 2003     

SALS,WAXS and mechanical properties of heat‐treated thermotropic polymers

The influence of heat treatment on the texture, microstructure and tensile mechanical properties of extruded thin films of a series of high‐performance thermotropic liquid crystal polymers (LCPs) was investigated. LCPs based on random units of hydroxybenzoic acid (B), hydroxynaphthoic acid (N), terephthalic acid (TA) and biphenol (BP) were kindly supplied by the former Hoechst Celanese Corp as 50 µm thick extruded tapes. The LCPs, denoted B‐N, COTBP and RD1000, have B and N as common comonomers and vary the other comonomers. Thus, this study also enables the investigation of the influence of monomer composition on microstructure and mechanical properties. Heat treatments were carried out at temperatures close to the solid‐to‐nematic transition (T_s→n) for periods up to 5 h, under dry air conditions. The thermal treatment produced either two endotherms or a small increase of T_s→n (B‐N and RD1000), or increased significantly T_s→n (COTBP). Moreover, when heat treatment was carried out approximately 40°C below the respective T_s→n, the mechanical Young's modulus, E, along the extrusion axis, increased for all LCPs. Strikingly, for COTBP, E increased over 100% relative to the as‐extruded film. The results also showed that the optimum treatment time for improving the Young modulus, under dry air atmosphere, was between 3 and 4 h. Wide‐angle X‐ray scattering showed a significant sharpening of crystalline reflections and concentration of the 002 meridional reflection as a result of thermal treatment, suggesting the elimination of defects and a better alignment of the molecular chains along the extrusion axis. This would explain the increase in tensile modulus. Copyright © 2013 John Wiley & Sons, Ltd.     

Mechanical properties of emulsion polymer blends

Polymer blend technology has been one of the most investigated areas in polymer science in the past 3 decades. The one area of polymer blends that has been virtually ignored involves simple emulsion blends, although several articles have recently appeared that address film formation and mechanical characteristics. In this study, we investigated the mechanical property behavior of emulsion blends composed of low/high‐glass‐transition‐temperature polymers (where low and high mean below and above the test temperature, respectively). The emulsions chosen for this study had similar particle sizes, and the mixtures were rheologically stable. Two conditions were chosen, a binary combination of polymers that were thermodynamically immiscible and another system that was thermodynamically miscible. The mechanical property results over the entire composition range were compared with the predictions of the equivalent box model (EBM) with the universal parameters predicted by percolation theory. An array of randomly mixed and equal‐size particles of differing moduli was expected to show excellent agreement with theory, and the emulsion blends provided an excellent experimental basis for testing the theory. For the immiscible blend, the EBM prediction for the modulus showed excellent agreement with experimental results. With tensile strength, the agreement between the modulus and theory was good if the yield strength for the higher glass‐transition‐temperature polymer was employed in comparison with the actual tensile strength. The phase inversion point (where both phases were equally continuous) was at a 0.50 volume fraction of each component (based on an analysis employing Kerner's equation), just as expected for a random mixture of equal‐size particles. © 2001 John Wiley & Sons, Inc. J Polym Sci B: Polym Phys 39: 1093–1106, 2001     

Effects of compatibility of poly(l‐lactic‐acid) and thermoplastic polyurethane on mechanical property of blend fiber

Blending poly(l ‐lactic‐acid) (PLLA) and thermoplastic polyurethane (TPU) has been performed in an effort to toughen PLLA without compromising its biodegradability and biocompatibility. The mixing enthalpy calculation of PLLA and TPU predicted that the blend was a thermodynamic miscible system. The viscoelastic properties and phase morphologies of PLLA/TPU blends were investigated further by dynamic mechanical analysis and scanning electron microscopy. It was found that the blend was a partially miscible system. The dynamic mechanical analysis showed that T_g of PLLA and TPU shifted toward with TPU content increasing. Scanning electron microscopy photos showed that the morphologies of the blends changed from a sea island structure to a bicontinuous structure as an increment in TPU content, which suggested that the miscibility of PLLA and TPU was enhanced when the TPU increased. PLLA/TPU blend fibers were fabricated. With the TPU content increasing from 0 wt% to 30 wt%, the tensile strength and initial modulus of blend fibers decreased first then increased, while elongation at break and fracture work gradually increased. The change of tensile properties indicated the toughening effects of TPU on PLLA fibers, also suggested that the formation of blend fibers was influenced by the blend rheological behavior other than the compatibility. Copyright © 2014 John Wiley & Sons, Ltd.     

Structure–property relationship in PCL/starch blend compatibilized with starch‐g‐PCL copolymer

The polycaprolactone (PCL)/starch blends were prepared by using the starch‐g‐PCL (SGCL) graft copolymers as compatibilizers, and their mechanical properties were correlated with the compatibilizing effect of the SGCL copolymers having various molecular structures. The modulus and strength of the PCL/starch blend were decreased, whereas the percent elongation and the toughness were increased remarkably with the addition of SGCL having appropriate graft structure. These property changes were analyzed in terms of the PCL crystallinity and the interfacial adhesion between the PCL matrix and starch dispersion phases, which were dominated by the compatibilizing effects of the SGCL copolymers. © 1999 John Wiley & Sons, Inc. J Polym Sci B: Polym Phys 37: 2430–2438, 1999     

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     

Evaluation of compatibility and properties of biodegradable polyester blends

Three different biodegradable polyesters, namely, polycaprolactone (PCL), polybutylene succinate (BIONOLLE), and a copolyester of adipic acid, terephthalic acid, and 1,4‐butanediol (EASTAR) were melt‐blended using a twin‐screw extruder. The percentage composition of each of the aforementioned polymers was varied to obtain different blends, and the mechanical properties were evaluated. Selected blends showed significant improvement in tensile strength as compared with the individual polymers used to prepare the blend. The compatibility between the polymer phases was examined via Fourier transform infrared (FTIR) and nuclear magnetic resonace (NMR) spectroscopy as well as dynamic mechanical analysis. FTIR and NMR data confirmed the occurrence of hydrogen‐bonding and ester‐interchange reactions. Thermal properties and changes in crystallinity of the blends were examined with differential scanning calorimetry and X‐ray diffraction. A considerable increase in crystallinity was shown by the blend system containing BIONOLLE/PCL. The morphology of the blends was observed and correlated to the improved mechanical properties of the blend system. Results revealed an intermediate multiphase system in which a significant degree of mixing was achieved through the chemical interaction of the functional groups present, while using the twin‐screw extruder. Significant improvement in mechanical properties of some blends was observed, and information about the miscibility of these polyesters is provided. © 2002 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 40: 2003–2014, 2002     

Fiber property and structure development of polyester blend fibers reinforced with a thermotropic liquid‐crystal polymer

Ternary blend fibers (TBFs), based on melt blends of poly(ethylene 2,6‐naphthalate), poly(ethylene terephthalate), and a thermotropic liquid‐crystal polymer (TLCP), were prepared by a process of melt blending and spinning to achieve high‐performance fibers. The reinforcement effect of the polymer matrix by the TLCP component, the fibrillar structure with TLCP fibrils of high aspect ratios, and the development of more ordered and perfect crystalline structures by an annealing process resulted in the improvement of the tensile strength and modulus for the TBFs. An increase in the apparent crystallite size with the spinning speed was attributed to the development of larger crystallites and more ordered crystalline structures in the annealed TBFs. The birefringence and density of the TBFs increased with increasing spinning speed, the TBFs becoming more oriented and the crystal packing becoming more enhanced. The molecular orientation was an important factor in determining the tensile strength and modulus of the TBFs. © 2003 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 42: 395–403, 2004     

Mechanical properties of polymer‐blend nanocomposites with organoclays: Polystyrene/ABS and high impact polystyrene/ABS

Thirty‐three polystyrene (PS)/acrylonitrile‐butadiene‐styrene (ABS) and high impact PS/ABS polymer blends with organoclay and copolymer additives were prepared by melt processing using different mixing sequences in order to test the putative capability of clay to perform a compatibilizing role in polymer blends. In general, the addition of clay increased the tensile modulus and had little effect on tensile strength. For the blends studied in this work, the addition of organoclays caused a catastrophic reduction in impact strength, a critical property for commercial viability. The polymer‐blend nanocomposites adopted a structure similar to that for ABS/clay nanocomposites as determined by X‐ray diffraction and transmission electron microscopy. It is suggested that clay reinforcement inhibits energy absorption by craze formation and shear yielding at high strain rates. Simultaneous mixing of the three components provided nanocomposites with superior elongation and energy to failure compared to sequential mixing. The clay pre‐treated with a benzyl‐containing surfactant gave the best overall properties among the various organoclays tested and of the two clay contents studied 4 wt % was preferred over 8 wt % addition. © 2011 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys, 2011     

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.     

A literature review on the in situ generation of reinforcing fibers

Liquid crystal polymers (LCPs) are a relatively new class of materials. These polymers usually consist of rigid rodlike molecular chains and they are capable of forming highly oriented structures even in the as-made product, with strength/modulus significantly higher than those of the conventional flexible chain polymers. Blending of LCPs with conventional polymers produces composite-like structures with LCPs serving as the reinforcing component. The properties of the blends are affected by the size, shape and distribution of the LCPs in the matrix polymer, which in turn are related to the processing conditions such as the blend composition, the extrusion and drawing conditions, the viscosity ratio of the component polymers and the type and grade of the LCPs and the matrix polymers. Improved processability of the blend due to the reduction in viscosity and the improved interfacial adhesion between reinforcing fibers and the matrix polymer are among the advantages of these materials over the conventional short fiber reinforced composites. This paper gives a brief review of the work currently available in the literature on rheology, fabrication, blend morphology and mechanical/thermal properties of the in situ composites from blends of LCPs and conventional polymers.     

Dynamic mechanical behavior of acrylonitrile butadiene rubber/poly(ethylene‐co‐vinyl acetate) blends

The dynamic mechanical behavior of uncrosslinked (thermoplastic) and crosslinked (thermosetting) acrylonitrile butadiene rubber/poly(ethylene‐co‐vinyl acetate) (NBR/EVA) blends was studied with reference to the effect of blend ratio, crosslinking systems, frequency, and temperature. Different crosslinked systems were prepared using peroxide (DCP), sulfur, and mixed crosslink systems. The glass‐transition behavior of the blends was affected by the blend ratio, the nature of crosslinking, and frequency. sThe damping properties of the blends increased with NBR content. The variations in tan δ_max were in accordance with morphology changes in the blends. From tan δ values of peroxide‐cured NBR, EVA, and blends the crosslinking effect of DCP was more predominant in NBR. The morphology of the uncrosslinked blends was examined using scanning electron and optical microscopes. Cocontinuous morphology was observed between 40 and 60 wt % of NBR. The particle size distribution curve of the blends was also drawn. The Arrhenius relationship was used to calculate the activation energy for the glass transition of the blends, and it decreased with an increase in the NBR content. Various theoretical models were used to predict the modulus of the blends. From wide‐angle X‐ray scattering studies, the degree of crystallinity of the blends decreased with an increasing NBR content. The thermal behavior of the uncrosslinked and crosslinked systems of NBR/EVA blends was analyzed using a differential scanning calorimeter. © 2002 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 40: 1556–1570, 2002     

Morphology and mechanical and viscoelastic properties of natural rubber and styrene butadiene rubber latex blends

The morphology and mechanical and viscoelastic properties of a series of blends of natural rubber (NR) and styrene butadiene rubber (SBR) latex blends were studied in the uncrosslinked and crosslinked state. The morphology of the NR/SBR blends was analyzed using a scanning electron microscope. The morphology of the blends indicated a two phase structure in which SBR is dispersed as domains in the continuous NR matrix when its content is less than 50%. A cocontinuous morphology was obtained at a 50/50 NR/SBR ratio and phase inversion was seen beyond 50% SBR when NR formed the dispersed phase. The mechanical properties of the blends were studied with special reference to the effect of the blend ratio, surface active agents, vulcanizing system, and time for prevulcanization. As the NR content and time of prevulcanization increased, the mechanical properties such as the tensile strength, modulus, elongation at break, and hardness increased. This was due to the increased degree of crosslinking that leads to the strengthening of the 3‐dimensional network. In most cases the tear strength values increased as the prevulcanization time increased. The mechanical data were compared with theoretical predictions. The effects of the blend ratio and prevulcanization on the dynamic mechanical properties of the blends were investigated at different temperatures and frequencies. All the blends showed two distinct glass‐transition temperatures, indicating that the system is immiscible. It was also found that the glass‐transition temperatures of vulcanized blends are higher than those of unvulcanized blends. The time–temperature superposition and Cole–Cole analysis were made to understand the phase behavior of the blends. The tensile and tear fracture surfaces were examined by a scanning electron microscope to gain an insight into the failure mechanism. © 2000 John Wiley & Sons, Inc. J Polym Sci B: Polym Phys 38: 2189–2211, 2000     

Biodegradable stereocomplex materials of polylactide‐grafted dextran exhibiting soft and tough properties in dry and wet states

Water‐swellable biodegradable materials exhibiting mechanically tenacious and tough characters in the wet state were prepared by a simple blend of two enantiomeric polylactide‐grafted dextran copolymers (Dex‐g‐PLLA and Dex‐g‐PDLA). DSC and WAXD analyses demonstrated the formation of SC crystals in the copolymer blend films. SC blend films showed lamellar‐type microphase‐separated structures. When swollen with water, these blend films showed the same level of tensile strengths and Young's modulus as the films in the dry state. SC blend films degraded gradually over a month under physiological conditions with a degradation rate faster than the corresponding Dex‐g‐PLLA films. The SC‐forming enantiomeric mixture of polylactide‐grafted polysaccharides should be a good candidate for an implantable biocompatible material exhibiting favorable mechanical properties and degradation behavior. © 2012 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2012     

Diglycidyl ether of bisphenol‐A epoxy resin modified using poly(ether ether ketone) with pendent tert‐butyl groups

Bisphenol‐A‐based difunctional epoxy resin was modified with poly(ether ether ketone) with pendent tert‐butyl groups (PEEKT). PEEKT was synthesized by the nucleophilic substitution reaction of 4,4′‐difluoro benzophenone with tert‐butyl hydroquinone in N‐methyl‐2‐pyrrolidone. Blends with various amounts of PEEKT were prepared by melt‐mixing. All the blends were homogeneous in the uncured state. The glass transition temperature of the binary epoxy/PEEKT blends was predicted using several equations. Reaction‐induced phase separation was found to occur upon curing with a diamine 4,4′‐diaminodiphenyl sulfone. The phase morphology of the blends was studied using scanning electron microscopy. From the micrographs, it was found that PEEKT‐rich phase was dispersed in a continuous epoxy matrix. The domain size increased with the amount of PEEKT in the blends. The increase in domain size was due to the coalescence of the domains after phase separation. Dynamic mechanical analysis of the blends gave two peaks corresponding to epoxy‐rich phase and thermoplastic‐rich phase. The tensile strength and modulus of the blends remained close to that of the unmodified resin, while the flexural properties decreased with the addition of PEEKT to epoxy resin. The fracture toughness of the epoxy resin increased with the addition of PEEKT. Investigation of the fracture surfaces revealed evidences for local plastic deformation of the matrix, crack pinning, crack path deflection, and ductile tearing of PEEKT‐rich phase. Thermogravimetric analysis revealed that the initial decomposition temperature of the blends were close to that of the unmodified resin. Finally, the properties of the blends were compared with other modified PEEK/epoxy blends. © 2007 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 45: 2481–2496, 2007     

Electrospun fiber mats of poly(3‐hydroxybutyrate), poly(3‐hydroxybutyrate‐co‐3‐hydroxyvalerate), and their blends

Electrospinning of poly(3‐hydroxybutyrate) (PHB), poly(3‐hydroxybutyrate‐co‐3‐hydroxyvalerate) (PHBV), and their blends was first carried out in chloroform at 50 °C on a stationary collector. The average diameter of the as‐spun fiber from PHB and PHBV solutions decreased with increasing collection distance and increased with increasing solution concentration and applied electrical potential. In all of the spinning conditions investigated, the average diameter of the as‐spun pure fibers ranged between 1.6 and 8.8 μm. Electrospinning of PHB, PHBV, and their blends was carried out further at a fixed solution concentration of 14% w/v on a homemade rotating cylindrical collector. Well‐aligned, cross‐sectionally round fibers without beads were obtained. The average diameter of the as‐spun pure and blend fibers ranged between 2.3 and 4.0 μm. The as‐spun fiber mats appeared to be more hydrophobic than the corresponding films and much improvement in the tensile strength and the elongation at break was observed for the blend fiber mats over those of the pure fiber ones. Lastly, indirect cytotoxicity evaluation of the as‐spun pure and blend fiber mats with mouse fibroblasts (L929) indicated that these mats posed no threat to the cells. © 2006 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 44: 2923–2933, 2006     

Preparation and characterization of melt‐compounded polyethylene/vermiculite nanocomposites

Polyethylene (PE)‐layered vermiculite (VMT) nanocomposites were fabricated via direct melt compounding in a twin‐screw extruder followed by injection molding. Exfoliated PE/VMT nanocomposites were readily prepared via in situ melt mixing of maleic anhydride modified VMT with PE. Maleic anhydride acts as either the intercalation agent for VMT or as a compatibilizer for the PE and VMT phases. X‐ray diffraction and transmission electron microscopic observations revealed the formation of exfoliated PE/VMT nanocomposites. The experimental results showed that the storage modulus and strength of nanocomposites tend to increase with an increasing VMT content. Nearly 25.35% increment in the tensile strength and 50% increment in the storage modulus were achieved by incorporating 4 wt % VMT into PE. The thermal properties of the nanocomposites were investigated by dynamic mechanical analysis and differential scanning calorimetry. The glass‐transition temperature of PE/VMT nanocomposites appeared to increase upon the introduction of VMT into the PE matrix. The effects of maleic anhydride addition on the formation of the PE/VMT nanocomposites are discussed. © 2003 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 41: 1476–1484, 2003     

Biodegradable polycaprolactone–polyanhydrides blends

Biodegradable polymers based on a blend of polycaprolactone (PCL) and aliphatic polyanhydrides with various monomer lengths were prepared to obtain desired polymer blends for use as drug carriers. The physicochemical, mechanical, and drug‐release properties of these blends were investigated by various techniques to evaluate the uniformity degree of the polymer blends to establish their potential applications in drug delivery. The results demonstrated that the heat of fusion (ΔH) of the polyanhydride or the blend is increased in relation to the length of the aliphatic chain. However, the blends had different properties than pure polyanhydride, and the crystallization degree of the blends, as expressed by the ΔH, decreased in relation to the ΔH of the pure polyanhydride. Drug‐release studies from blends of PCL and aliphatic polyanhydrides demonstrated first‐order kinetics of the release rate. Polymer degradation was independent at the polyanhydride monomer length. On the basis of theoretical calculation of the interaction factor, a blend of PCL and poly(dodecanedeoic anhydride) was chosen for further elucidation of its thermal, mechanical, and degradation properties. © 2003 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 41: 3781–3787, 2003