Mechanical and swelling properties of thermoplastic elastomer blends

The mechanical behavior, microhardness and abrasion resistance of acrylonitrile butadiene rubber (NBR) vulcanizate loaded with 40 phr fast extrusion furnace (FEF) carbon black nanopowder and different concentrations of suspension polymerization polyvinyl chloride (PVC) were studied. The measured parameters (i.e., the Young’s modulus, tensile strength, and elongation at break) varied with the concentration of PVC. Both the elastic modulus and the tensile strength increased with increasing PVC loadings while the elongation at brake recorded a linear decrease. The hardness degree and the abraded mass increased as the concentration of PVC increased. The classical theory of rubber elasticity was used to calculate the rubbery modulus, the number of effective chains per unit volume and the average molecular weight. Swelling measurements were done on the mentioned samples. Addition of PVC was found to decrease the maximum degree of swelling, the penetration rate and the average diffusion coefficient. Swelling was found to slightly affect the degree of hardness and elastic modulus.     

Compatibility and morphology of blends of isotactic and atactic polypropylene

The compatibility and morphology of blends of isotactic and atactic polypropylene have been studied by several means: X-ray scattering, differential scanning calorimetry, and electron microscopy. It was found that the atactic polymer was located mainly inside the spherulites of the isotactic polypropylene on a scale approximately equal to that of the crystalline lamellae. This means that these two polymers were more intimately mixed than are blends of polypropylene and ethylene-propylene copolymer, in which the location of the copolymer is unrelated to the spherulite structure. This difference can be explained by the fact that atactic and isotactic polypropylene are miscible in the melt, whereas polypropylene and ethylene-propylene copolymer are not.     

Strength of thermoplastic elastomers from rubber-polyolefin blends

The strength of different thermoplastic elastomers of varying compositions and interactions has been examined over a wide range of rates and temperatures and for a wide variety of test configurations. Fracture energy was calculated from various test specimens and found to be similar, and independent of the test configuration. Fracture energy values lie between 0.8 and 120kJm_–2. The behaviour could be compared with that of rubbers. However, for a trouser-tear test piece, the fracture energy increases with increasing thickness of the torn path in the very small thickness region, as for the fracture of polyethylene. The fracture surface morphology of various composites indicates different mechanisms of crack propagation. The tensile rupture data over a wide range of rates and temperatures could be represented by a single parabolic curve — the failure envelope. The maximum elongation at break and tensile strength of the composites are related to the modulus.     

Effect of elastomer on polypropylene/nylon-12 blends

Various compositions of polypropylene (PP)/nylon-12 blends with elastomer were prepared. Morphologies and mechanical properties of the blends were studied. In particular, the effect of ethylene-propylene (EP) elastomer and maleic anhydride-grafted ethylene propylene elastomer (Ma-g-EP) on the PP/nylon-12 blends were investigated. The results showed that PP/nylon-12 blends have inferior mechanical properties because of their poor compatibility and dispersion. The EP elastomer has a limited effect on the blends since the mechanical properties of PP/nylon-12 blends were controlled by their interface. The Ma-g-EP elastomer improved the mechanical properties of PP/nylon-12 blends through improvement of the interface between PP and nylon-12, and compatibility between the elastomer and nylon-12. Differential scanning calorimetry (DSC) and scanning electron microscopy (SEM) were used to characterize microstructures. The dispersion of components and the compatibility between PP and nylon-12 were significantly improved with addition of the Ma-g-EP elastomer.     

The effect of compatibilizers on the morphology of isotactic polypropylene/linear low-density polyethylene blends

The morphology of isotactic polypropylene (iPP)/linear low-density polyethylene (LLDPE) blends, compatibilized with ethylene-propylene block copolymer (EP) and two types of styrene-ethylene/butylene-styrene triblock copolymer (SEBS), one containing maleic anhydride, the other no reactive sites, has been investigated by using small-angle X-ray scattering by evaluating their interface distribution functions. To characterize the crystallization behaviour of the blends, their spherulitic growth rates have been measured under the polarizing microscope and nucleation and crystallization kinetics data have been evaluated. The addition of LLDPE to iPP alone has a pronounced effect on the lamellar morphology of the iPP. Adding compatibilizer to the iPP/LLDPE blend leads to a further decrease of the lamellar thickness. Concurrently the nucleation density increases while the Avrami exponent drops from n2.3 for iPP to n=0.74 for the iPP/LLDPE/SEBS blend. It is concluded that the compatibilizer causes the polyethylene component to become more highly dispersed in the polypropylene matrix.     

Morphology and mechanical properties of isotactic polypropylene glass mat thermoplastic composites modified with organophilic montmorillonite

Satisfactory impregnation of glass fiber mats may be obtained with isotactic polypropylene/montmorillonite (MMT) nanocomposites under conditions comparable with industrial conditions. However, it is demonstrated here that the high melt viscosity of the nanocomposite matrix at low shear rates may significantly influence the release of the compressive load in the glass mat and hence the glass fiber distribution in consolidated specimens. Thus, depending on the initial lay-up and overall glass fiber content, the bending modulus may either increase or decrease with increasing MMT content, whereas the tensile modulus is more consistent with micromechanical models assuming a uniform glass fiber distribution. Results from fractographic analyses show that the presence of matrix rich layers at the specimen surfaces may also lead to premature crack initiation and failure in flexion.     

Effect of crosslinking on morphology and phase inversion of EPDM/PP blends

This study investigates the effect of cross-linking on morphology and phase inversion of EPDM/PP blends. Several EPDM/PP blends without and with cross-linking agent were prepared in a Haake batch mixer under constant conditions. The morphology was studied by electronic microscopy (SEM and TEM), and cross-linking was followed by EPDM gel content and swelling. The results showed that the position of the phase inversion region is essentially governed by composition, being independent of the viscosity ratio of the EPDM/PP blend. The TPVs’ morphology of the EPDM/PP blend, with 70 and 50 wt% of PP, consists of EPDM cross-linked particles dispersed in the PP matrix. For EPDM-rich composition (30 wt% of PP), the TPVs’ morphology appears to be co-continuous. Even though dynamic vulcanisation of the rubber phase always improves the dispersion of the EPDM phase, complete phase inversion (from fully dispersed PP in the EPDM matrix to EPDM fully dispersed in the PP matrix) was achieved only with low viscosity EPDM.     

Vibration-dependent morphology and crystal structure of isotactic polypropylene

A small homemade device was used to study the influence of mechanical vibration on the crystal structure and morphology of isotactic polypropylene (iPP) under different melting temperatures, vibration times, vibration frequencies, and cooling rates. The crystallite size, crystal structure, and crystallinity of iPP under or without vibration treatment were investigated by means of differential scanning calorimetry (DSC), wide angle X-ray diffraction (WAXD), and polarized microscopy observation (PLM). The crystallization of iPP varied with the length of vibration time, vibration frequency, cooling rate, and melt temperature. Compared with the data of conventional samples measured by DSC, vibration could increase the crystallinity of iPP, make melting peak of α-crystal move toward higher temperature and make that of β-crystal shift to lower temperature. Meanwhile, WAXD measurements showed that the vibration could reduce the content of β-crystal evidently, particularly at the lower vibration frequency, lower cooling rate, and higher melting temperature. Furthermore, PLM measurements showed that the vibration made the spherulite size smaller.     

Scanning electron microscopy studies on tensile failure of thermoplastic elastomers from polypropylene-natural rubber blends

The tensile properties of thermoplastic polypropylene [pp]-natural rubber [NR]blends have been evaluated with special reference to the effect of blend ratios and dynamic cross-linking of the elastomer phase. The effects of silica filler and silane coupling agent on the tensile properties of the 30:70 PP:NR blend have also been studied. Analysis of the stress-strain curves and scanning electron microscopic examination of the tensile fracture surfaces of the blends have been used to correlate the test results on tensile properties.     

Isotactic polypropylene/EPDM blends: Effect of testing temperature and rubber content on fracture

Charpy impact tests in the temperature range ?100 to +20° C have been carried out on two isotactic polypropylenes (PP) having different molecular weight and their blends containing as rubbery phase an ethylene-propylene-diene terpolymer (EPDM). For fractures of brittle nature the impact data were analysed in terms of the linear elastic fracture mechanics andK _c andG _c were determined. This behaviour was observed for the homopolymers over the temperature range investigated, and for the blends only up to ?20° C. At higher temperatures such materials showed fracture of a semiductile type with visible evidence of craze whitening around the crack tip, followed by brittle type fracture. In this case the results were analysed in terms of a ductile contribution (energy required to form the crazed area) and of a brittle one (relative to the crack propagation area) from whichG _c could be derived according to a procedure proposed in the literature. Tentative interpretations of the results also on a molecular and structural basis have been given. A critical discussion of the elaboration of the semiductile fracture data proposed in the literature has also been provided.     

The effect of ultra-thin graphite on the morphology and physical properties of thermoplastic polyurethane elastomer composites

Composites of thermoplastic polyurethane (TPU) and ultra-thin graphite (UTG) with concentrations ranging from 0.5 wt.% to 3 wt.% were prepared using a solution compounding strategy. Substantial reinforcing effects with increased loadings are achieved. Compared to neat TPU, values for storage modulus and shear viscosity are enhanced by 300% and 150%, respectively, for UTG concentrations of 3 wt.%. Additionally, an enhancement of thermal properties is accomplished. The crystallization temperature and thermal stability increased by 30 °C and 10 °C, respectively, compared to neat TPU. Furthermore, the use of oxidized UTG (UTGO) with its added functional oxygen groups suggests the presence of chemical interactions between UTG and TPU, which additionally impact on the thermal properties of the corresponding composites. Controlling the oxidation degree, thus offers further possibilities to obtain composites with tailored properties. The presented approach is straightforward, leads to homogeneous TPU-UTG composites with improved materials properties and is especially suitable for commercial UTG materials and further up-scaled production.     

Microstructure and mechanical properties of isotactic polypropylene (iPP)/polyamide 12 (PA12) blends

The microstructure and mechanical properties of polyamide 12/isotactic polypropylene blends with different compositions are studied. It is shown that the injection moulding technique used to process all samples results in a more or less pronounced orientation of macromolecular chains, which in its turn is responsible for a preferential orientation of polymer crystals. At a larger scale, the injection technique is also responsible for the deformation of polyamide domains into ellipsoides when polypropylene is dominant. In contrast, when polyamide is dominant, domains of both polymers are co-continuous in the materials. This feature is discussed on the basis of dynamic mechanical measurements.     

Effect of morphology on the behaviour of ternary composites of polypropylene with inorganic fillers and elastomer inclusions

The effects of phase morphology, interfacial adhesion, rigid filler particle shape and elastomer volume fraction on the tensile yield strength of polypropylene (PP) filled with inorganic filler (CaCO₃ or Mg(OH)₂) and ethylene-propylene elastomer (EPR) were investigated. Separation of the filler and elastomer particles was achieved using maleic-anhydride-grafted PP (MPP) to enhance the filler-matrix adhesion. Encapsulation of the rigid filler by the elastomer was achieved using maleic-anhydride-grafted EPR (MEPR) to increase the filler-elastomer adhesion. The two limiting morphologies differ significantly in mechanical properties under tensile loading at the same material composition. Elastomer particles separately dispersed in the matrix enhance the shear banding in the bulk matrix which prevents the crazes growing from the filler surface from becoming unstable and, thus, increases the ductility of the material. Encapsulation by an elastomer layer on the filler surface relieves triaxial stresses at the filler surface, changing the major local failure mechanism from crazing to shear yielding and, hence, increasing the ductility of the material. Increase of the elastomer volume fraction also causes, in both cases, an increase in matrix ductility. Composite models are used to predict upper and lower limits of yield strength (_y) for the two limiting morphologies over an interval of elastomer volume fractions (V _e) from 0 to 0.2 at a constant filler loading of 30 vol.% and over a filler volume fraction from 0 to 0.4 at a constant EPR content in the matrix. Satisfactory agreement was found between the experimental data and theoretical predictions.     

Effect of dynamic crosslinking on crystallization and thermal degradation of polypropylene in polypropylene (PP)/ethylene-propylene DIENE (EPDM) rubber blends

Blends of isotactic polypropylene and ethylene propylene diene (EPDM) rubber were dynamically vulcanized using the dimethylol phenolic resin/stannous chloride crosslinking system. The EPDM blends are thermally more stable than polypropylene (PP). Dynamic curing rendered the vulcanizate thermally more stable than unvulcanized blends. The variations in degree of crosslinking and degree of crystallinity are the main factors for observed increase in thermal stability of vulcanized blends. Degree of crosslinking increases the interfacial adhesion between the PP and EPDM phases. Dimethylol phenolic resin used as a compatibilizer also enhanced the thermal stability of the PP/EPDM blends. Crystallization of PP in the blends of PP/EPDM was also studied through modulated differential scanning calorimetry. Other detailed analyses of endotherm peaks obtained after first and second melts in terms of heat of enthalpy, degree of undercooling, and degree of crystallinity were also evaluated. Kinetic parameters were also determined.     

聚氨酯-聚乳酸共混物的制备及性能

通过熔融共混挤出法制备不同质量比的热塑性聚氨酯-聚乳酸(TPU-PLA)共混物,采用SEM、DSC、TG、微卡软化点温度测定仪和熔融流动速率仪对共混物的表面形态结构、热学、高温加工等性能进行研究。结果表明:TPU-PLA共混物表面光滑且呈现出脆性断裂形貌特征,共混体系两种高聚物呈"海岛"分布;TPU-PLA共混体系中PLA与单独PLA相比,玻璃化转变温度Tg由69.60℃(Original PLA)变为57.58℃(PLA70)、53.29℃(PLA50)和55.64℃(PLA30),TPU均匀分散于PLA基体中且相界面分明,这都说明TPU-PLA共混体系为部分相容体系;TPU-PLA共混物的热失重起始分解温度范围为180~200℃,最快分解温度范围为310~350℃,热稳定性良好;TPU含量占共混物10%~30%时,共混物高温的临界变形温度相对单一体系有所提高;随TPU含量的继续增加,共混物熔融指数呈现先增大后减小的变化趋势,其中PLA与TPU质量比为4∶6的TPU-PLA共混物熔融指数达到最大,为1 406g·(10min)-1。