Biodegradable Poly(3-hydroxybutyrate) Nanocomposite

This work seeks bringing a technological and social contribution by searching blends and composites of poly(3-hydroxybutyrate) (PHB) and polyethylene widely used in packaging films, and colloidal silica. The mixtures were prepared by extrusion using a single-screw extruder and were analyzed regarding their thermal and mechanical properties and morphology. The results have shown PHB toughness in the studied compositions, which elongation at break was in the range 5–80% compared to 2% for neat PHB. The small amount (0.2 to 0.4%) of added silica seemed to increase in 20% the tensile strength. The thermal degradation by thermogravimetry from room temperature to 800 °C revealed a mixed behavior for the composites between PHB and polyethylene.     

Influence of poly (ethylene glycol) on the thermal, mechanical, morphological, physical-chemical and biodegradation properties of poly (3-hydroxybutyrate)

Blends of poly (3-hydroxybutyrate) (PHB) with poly (ethylene glycol) (PEG), (PHB/PEG), in different proportions of 100/0, 98/2, 95/5, 90/10, 80/20 and 60/40 wt%, respectively, were investigated for their thermal properties (using differential scanning calorimetry and thermogravimetric analysis), tensile properties, water vapor transmission rate, enzymatic biodegradation (using light microscopy) and mass retention. The addition of plasticizer did not alter the thermal stability of the blends, although an increase in the PEG content reduced the tensile strength and increased the elongation at break of pure PHB.     

Thermal and mechanical properties of polypropylene in the thermoplastic elastomeric state

One result of the discovery of homogeneous metallocene stereospecific catalysts is the ability to prepare polypropylene in a stereoblock form in which the isotactic stretches give crystallites acting as temporary crosslinks in an elastomeric network structure. The fact that these elastomers are thermoplastic and thus reprocessible increases the importance of establishing their structure-property relationships. In this report, the dependence of their physical properties on isotactic pentad content, molecular weight, and possible strain-induced crystallization are described. Thermal evaluations and mechanical tests of these materials under oscillatory strain, continuous extension and near-equilibrium uniaxial and biaxial elongation showed that they were multiphase, tough elastomeric materials. Their moduli and tensile strengths increased with increase in % isotactic pentad content and with increase in molecular weight. Equilibrium stress-strain measurements showed the occurrence of strain-induced crystallization in uniaxial, but not in biaxial, deformations.     

Thermomechanical behavior of metallocene ethylene-α-olefin copolymers

The thermal, dynamic mechanical and stress-strain properties of a set of commercial LLDPEs prepared by metallocene catalysts were studied and compared with two LLDPEs obtained with traditional Ziegler-Natta catalysts. The type and amount of comonomer strongly affects the degree of crystallinity and branching, resulting in different material morphology and macroscopic thermomechanical behavior. Within each set of ethylene-α-olefin copolymers a gradual decrease in the percentage crystallinity and position and intensity of β- and γ-transition is observed, with respect to the comonomer content. In addition, the studied materials are characterized by the absence of an α-transition. This behavior is attributed to the high comonomer content (5-24)%. Tensile behavior changes from the typical necking, cold drawing and strain hardening to the uniform elastomeric deformation, as the comonomer content increases.The experimental methods used, in combination with scanning electron microscopy, lead to converged results, while tensile testing proved to be sensitive to the crystallite size and distribution.     

Cure characteristics and properties of NBR composites filled with co‐precipitates of black liquor and montmorillonite

Acrylonitrile‐butadiene rubber (NBR) composites filled with co‐precipitates of black liquor and montmorillonite (CLM) were prepared by mechanical mixing on a two‐roll mill. The cure characteristics, mechanical properties, thermal properties, and thermo‐oxidative aging properties of NBR/CLM composites were evaluated. Scanning electron microscopy and transmission electron microscopy showed that the filler particles were well dispersed in the NBR/CLM composites. The scorch time and optimum cure time increase with increasing filler loading. A remarkable enhancement in tensile strength, elongation at break, 300% modulus, and shore “A” hardness was also observed. When the loading of CLM was 40 parts per hundred rubbers, it showed about seven times increase in tensile strength, about 1.8 times increase in elongation at break, about three times increase in 300% modulus, and about 1.3 times increase in shore A hardness, respectively, as compared with those of pure cured NBR. Thermal properties and thermal oxidative aging properties, in general, were also improved with loading of this novel filler. Copyright © 2011 John Wiley & Sons, Ltd.     

EPR-g-PS热塑弹性体结构与性能的关系

通过聚苯乙烯大分子单体与乙烯、丙烯共聚得到的乙丙橡胶(EPR)为主干、聚苯乙烯(PS)为支链的接枝共聚物EPR-g-PS,在无化学交联的情况下,模压样品具有与三元乙丙硫化胶可比拟的强度(PS=37.5％,M_(300％)=113公斤/厘米~2,抗张强度=198公斤/厘米~2,伸长率=705％)。聚苯乙烯含量、平均支链数目和成型条件是影响接枝共聚物力学性能的主要因素。聚苯乙烯微区除了以热塑交联网络起到物理交联作用外,在应力作用下本身还发生非弹性形变,起到补强填料的作用,使EPR-g-PS表现出热塑弹性体的性质。     

Efficient barrier properties of mechanically enhanced agro-extracted cellulosic biocomposites

The objective of this work was to prepare the mechanically stable hydrophobic biocomposites by incorporating the cellulose fibers into the polymer matrices for their applications in biomedical and food packaging. Herein, two different types of biocomposites were prepared by mixing polylactic acid (PLA) and polyhydroxybutyrate (PHB) with the agro-extracted cellulose, separately at 170 °C. The influence of the cellulose fibers on the thermal, mechanical, and barrier properties of polymer matrices (PLA and PHB) was observed. With an increase in the cellulose content in PLA and PHB, the tensile strength of the biocomposite materials significantly improved with the enhancement of 24.45% and 32.08%, respectively, compared with the pure PLA and PHB. Furthermore, a decrease of 74.16% and 73.49% in the water vapor transmission rate and oxygen transmission rate, respectively, was observed for cellulose/PHB biocomposites. This study highlights that adding cellulose fibers significantly improves the mechanical and the barrier properties of PLA and PHB, suggesting their biocomposites for use in biodegradable polymer industries.     

聚氨酯弹性体力学性能影响因素探讨

研究了合成方法、原料的种类与配比、硫化工艺条件等因素对聚氨酯弹性体力学性能的影响。结果表明,聚氨酯弹性体的结构与组成以及由此引起的微相分离程度的变化是影响弹性体性能的重要因素。对于同样的聚合多元醇、二异氰酸酯及扩链剂合成的弹性体,采用不同的硫化及熟化条件其力学性能不同,并找到达到最佳力学性能所需的工艺条件。     

Effect of poly(vinyl acetate) (PVAc) on thermal behavior and mechanical properties of poly(3-hydroxybutyrate)/poly(propylene carbonate) (PHB/PPC) blends

To assess the compatibility of blends of synthetic poly(propylene carbonate) (PPC), with a natural bacterial poly(3-hydroxybutyrate) (PHB), a simple casting procedure of blend was used. poly(3-hydroxybutyrate)/poly(propylene carbonate) blends are found to be incompatible according to DSC and DMA analysis. In order to improve the compatibility and mechanical properties of PHB/PPC blends, poly(vinyl acetate) (PVAc) was added as a compatibilizer. The effects of PVAc on the thermal behavior, morphology, and mechanical properties of 70PHB/30PPC blend were investigated. The results show that the melting point and the crystallization temperature of PHB in blends decrease with the increase of PVAc content in blends, the loss factor changes from two separate peaks of 70PHB/30PPC blend to one peak of 70PHB/30PPC/12PVAc blend. It is also found that adding PVAc into 70PHB/30PPC blend can decrease the size of dispersed phase from morphology analysis. The result of tensile properties shows that PVAc can increase the tensile strength and Young’s modulus of 70PHB/30PPC blend, and both the elongation at break and the tensile toughness increase significantly with PVAc added into 70PHB/30PPC.     

Liquid crystal polymers. I. Preparation and properties of p-hydroxybenzoic acid copolyesters

High molecular weight copolyesters were prepared by the acidolysis of poly(ethylene terephthalate) with p-acetoxybenzoic acid and polycondensation through the acetate and carboxyl groups. The mechanical properties of the injection-molded copolyesters containing 40–90 mole- % p-hydroxybenzoic acid (PHB) were highly anisotropic and dependent upon the PHB content, polyester molecular weight, injection-molding temperature, and specimen thickness. As the injection-molding temperature increased and the specimen thickness decreased, the tensile strength, stiffness, and Izod impact strength increased when measured along the direction of flow of the polymer melt, and the coefficient of thermal expansion was zero. In some compositions these properties were superior to those of commercial glass fiber reinforced polyesters. Maximum tensile strengths, flexural moduli, notched Izod impact strengths, and minimum melt viscosities were obtained with polyesters containing 60–70 mole-% PHB. Higher oxygen indicies (39-40) and heat deflection temperatures (150-220°C) were obtained with 80–90 mole-% PHB.     

Effect of PHB on the properties of biodegradable PLA blends

Blends of biodegradable polymers polylactic acid/thermoplastic starch/polyhydroxybutyrate (PLA/TPS/PHB) were prepared using a twin-screw extruder. The TPS content was constant (50 %) and the PHB content in the blends was gradually changed from 0 mass % to 20 mass %. TPS was prepared by melting, where a mixture of native starch, water and glycerol was fed into the twinscrew extruder. Average temperature of extrusion was 180°C and the concentration of glycerol was 40 mass %. Influence of the PHB concentration in the blend and that of the processing technology on the mechanical and rheological properties of the PLA/PHB composition containing TPS were studied. Mechanical properties were measured 24 h after the film and monofilament preparation and also after the specific storage time to study the effect of storage on the properties. The results indicate that differences in morphology strongly influence the mechanical properties of the studied materials with identical material composition.     

Thermoplastic elastomer based on epoxidized natural rubber/thermoplastic polyurethane blends: influence of blending technique

Epoxidized natural rubber (ENR) and thermoplastic polyurethane (TPU) blends were prepared by simple blend and dynamic vulcanization. The main objective was to prepare a low‐hardness TPU material with good damping and elastic and mechanical properties. It was found that the incorporation of ENR into the blend shows a reduction in Young's modulus, hardness (i.e. <70 Shore A), damping properties (i.e. tan δ < 0.3), and tension set (i.e. <20%) compared with the pure TPU. This indicates the formation of softer TPU materials with superior damping and elastomeric properties. However, incorporation of ENR sacrificed mechanical properties in terms of tensile strength and elongation at break, but these still remain in the range of applicability for industrial uses. It was also found that dynamic vulcanization caused enhancement of mechanical properties, relaxation, damping, rheological properties, and elasticity of the blends. Temperature scanning stress relaxation measurements revealed an improvement in stress relaxation properties and thermal resistance of the dynamically cured ENR/TPU blend. Copyright © 2011 John Wiley & Sons, Ltd.     

Correlative analysis between morphology and mechanical properties of poly-3-hydroxybutyrate (PHB) blended with polycarprolactone (PCL) using solid-state NMR

Blends of poly(3-hydroxybutyrate) (PHB) and poly(caprolactone) (PCL) were evaluated using multiscale instrumental analyses to reveal the effects of blend ratio and crosslinking reagent. In the multiscale instrumental analyses, molecular mobility from molecular to nano scales was examined by solid-state NMR, while the morphology at the micron scale was revealed by scanning electron microscopy (SEM). PHB-rich blends adopted a sea-island morphology and showed a larger maximum stress due to dispersed PHB filler. A PCL-rich blend also adopted a sea-island morphology but the sea domain consisted of PCL and showed a larger strain at break. An equal ratio PHB/PCL blend had a bicontinuous morphology which showed lower maximum stress and lower strain at break because of large hemispherical defects. The crosslinking reagent changes these heterogeneous morphologies of PHB/PCL blends to homogeneous at the micron scale, which improved tensile properties. Even though the molecular mobility changed with the polymer content and the crosslinking reagent, the bicontinuous and homogeneous morphologies more significantly affected the tensile properties of the PHB/PCL blends.     

Liquid crystal polymers. I. Preparation and properties of p-hydroxybenzoic acid copolyesters

High molecular weight copolyesters were prepared by the acidolysis of poly(ethylene terephthalate) with p-acetoxybenzoic acid and polycondensation through the acetate and carboxyl groups. The mechanical properties of the injection-molded copolyesters containing 40–90 mole-% p-hydroxybenzoic acid (PHB) were highly anisotropic and dependent upon the PHB content, polyester molecular weight, injection-molding temperature, and specimen thickness. As the injection-molding temperature increased and the specimen thickness decreased, the tensile strength, stiffness, and Izod impact strength increased when measured along the direction of flow of the polymer melt, and the coefficient of thermal expansion was zero. In some compositions these properties were superior to those of commercial glass fiber reinforced polyesters. Maximum tensile strengths, flexural moduli, notched Izod impact strengths, and minimum melt viscosities were obtained with polyesters containing 60–70 mole-% PHB. Higher oxygen indicies (39–40) and heat deflection temperatures (150–220°C) were obtained with 80–90 mole-% PHB.     

Graphene oxide/epoxy composites with enhanced fracture toughness for liquid hydrogen storage

Graphene oxide (GO)/epoxy composites cured by aliphatic dibasic acids have been prepared. The influences of structure of aliphatic dibasic acid and loading of GO on curing process and mechanical properties of epoxy composites were studied. The results show that the reaction activities, gel time of corresponding epoxy-acid system and tensile strength of the formed epoxy resins decrease with the increase of the chain length of aliphatic dibasic acids. Both fracture toughness (>1.96 MPa⋅m^1/2) and elongations at break (>6%) increase with the increase of the chain length of aliphatic dibasic acids. The introduction of GO is helpful to increase the mechanical properties and the gas transmission coefficient of GO/epoxy composites. A maximum of tensile strength and elongations at break were obtained when the loading of GO is 0.6 wt%. The gas transmission coefficient of GO/epoxy composite increases with the increase of GO loading. The excellent mechanical properties and gas leakage resistance coefficient of the formed epoxy composites provides potential application in many fields where conventional brittle epoxy resins are inapplicable.     

Dielectric,magnetic and mechanical properties of ferrite composites

The dielectric and magnetic properties of carbonyl—iron (CI) and nickel zinc ferrite polymer composites were studied with respect to the ferrite particulate content and microwave frequency. From the experimental data and using empirical models that relate the composite dielectric and magnetic properties, the respective dielectric and magnetic properties of the neat fillers were estimated. The tensile properties of the particulate composites comprising CI were shown to follow qualitatively Mooney's equation for the elastic modulus. The tensile strength of an elastomeric polyurethane and PVC composites containing CI increased with particulate content, while the elongation to break decreased with filler content. SEM micrographs of tensile fracture surfaces indicated that somewhat better adhesion is obtained in the case of the polyurethane-based composites compared to the PVC ones.     

Hydrogen bonding and mechanical properties of thin films of polyether-based polyurethane-silica nanocomposites

Two series of thin films of polyether-based polyurethane-silica nanocomposites having hard segment content of 51% and 34% and different concentrations of SiO₂ nanoparticles (0, 0.5, 1.0 and 3.0 vol.%) have been prepared. Infrared linear dichroic (LDIR) ratio, mechanical and differential scanning calorimetry (DSC) measurements were performed in order to determine the influence of hydrogen bonding on their mechanical and thermal properties. The degree of phase separation (DPS) and orientational functions in dependence on strain were calculated from the polarized IR spectra. The presence of silica nanoparticles gives rise to significant differences in the mechanical (stress-strain) properties of the nanocomposites with regard to the pure polymer. The nanocomposite thin films with lower hard segment content (HSC) displayed decreased stiffness and tensile and increased elongation at break in comparison to the nanocomposites with higher HSC. There was no distinctive influence of nanoparticles on the glass transition temperatures of soft segments. Nanosilica significantly affected the melting behavior of the hard phase only in samples with higher HSC.     

Mechanical properties of amphiphilic urethane acrylate ionomer hydrogels having heterophasic gel structure

Amphiphilic urethane acryale hydrogels containing ionic groups (dimethylolpropionic acid) were prepared by varying the molecular weight of the soft segment (polyether type) and the type of diisocyanate, and their mechanical properties were examined. They showed heterophasic gel structure composed of ionic hard domains induced by aggregation of the ionic groups and polyether soft domains comprising the urethane acrylate network. This heterophasic structure could be confirmed by dynamic mechanical analysis (DMA) and by wide-angle X-ray scattering analysis (WAXS); the crystallinity detected by WAXS and the transition peak of the ionic hard domains detected by DMA strongly suggested that there were ionic aggregates. These ionic aggregates acted as reinforcing fillers in the network, which eventually enhanced the tensile strength of the hydrogels. Above all, the tensile properties of the hydrogels were of interest in that the trends of the stress-strain curves were consistent with the rubbery ones. It is believed that the higher purity of the polyether soft domains resulted from the heterophasic gel structure imparting further elastomeric properties on the network. Received: 31 July 1998 Accepted in revised form: 15 October 1998     

Completely biodegradable composites of poly(propylene carbonate) and short,lignocellulose fiber Hildegardia populifolia

The composites of biodegradable poly(propylene carbonate) (PPC) reinforced with short Hildegardia populifolia natural fiber were prepared by melt mixing followed by compression molding. The mechanical properties, thermal properties, and morphologies of the composites were studied via static and dynamic mechanical measurements, thermogravimetric analysis, and scanning electron microscopy (SEM) techniques, respectively. Static tensile tests showed that the stiffness and tensile strength of the composites increased with an increasing fiber content. However, the elongation at break and the energy to break decreased dramatically with the addition of short fiber. The relationship between the experimental results and the compatibility or interaction between the PPC matrix and fiber was correlated. SEM observations indicated good interfacial contact between the short fiber and PPC matrix. Thermogravimetric analysis revealed that the introduction of short Hildegardia populifolia fiber led to a slightly improved thermooxidative stability of PPC. © 2004 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 42: 666–675, 2004