Thermoplastic vulcanizates based on maleated natural rubber/polypropylene blends: Effect of blend ratios on rheological,mechanical, and morphological properties

Maleated natural rubber (MNR) was prepared and used to formulate thermoplastic vulcanizates (TPVs) based on various MNR/PP blends. The influence of mixing methods on the TPVs properties was first studied. We found that mixing all ingredients in an internal mixer provided the TPVs with better mechanical properties. The final mixing torque, shear stress, and shear viscosity of the TPVs prepared with various blend ratios of MNR/PP increased with increasing levels of MNR in the blends. This may be attributed to higher shear viscosity of the pure MNR than that of the pure PP. Furthermore, as evidenced in SEM micrographs, the TPVs are two phase morphologies with dispersed small vulcanized rubber domains in the PP matrix. Therefore, the higher content of PP caused the more molten continuous phase of the flow during mixing and rheological characterization. Tensile strength and hardness of the TPVs increased with increasing levels of PP, while the elongation at break decreased. Furthermore, the elastomeric properties, in terms of tension set, increased with increasing levels of MNR in the blends. This may be attributed to decreasing trends in the size of vulcanized rubber particles dispersed in the PP matrix with an increasing concentration of MNR. POLYM. ENG. SCI. 46:594–600, 2006. © 2006 Society of Plastics Engineers.     

Monolithic silicon carbide with interconnected and hierarchical pores fabricated by reaction-induced phase separation

Hierarchically porous silicon carbide (SiC) monoliths were fabricated based on polycarbosilane (PCS), divinyl benzene (DVB), and decalin, by a sequence of procedures including catalyst-free hydrosilylation reaction-induced phase separation, ambient-pressure drying, calcination, and HF etching. The influences of ratios of each component on the phase separation were systematically studied. It was found that isotactic polypropylene added as a nonreactive additive could effectively tailor the microstructure and improve the mechanical properties of SiC monoliths. The resultant SiC monoliths mainly consisted of β-SiC nanocrystals, and possessed low bulk density (0.7 g/cm³), high porosity (78%), large specific area (100.6 m²/g), high compressive strength (13.5 ± 1.6 MPa), and hierarchical pores (macropores around 350 nm, mesopores around 4 and 20 nm). These properties make SiC monoliths promising materials for catalyst/catalyst support, gas separator, and the reinforcement of high-temperature composites.     

Compatibilizing agents in polymer blends: Interfacial tension,phase morphology,and mechanical properties

The interfacial tension, phase morphology, and phase growth was determined for four polymer blend systems: polyethylene/polystyrene, polyethylene/polyamide-6, polystyrene/polyamide-6, and polystyrene/poly(ethylene terephthalate). Generally, high interfacial tension correlates with coarse phase morphology and rapid phase coalescence. The addition of various potential compatibilizing agents to these binary blend systems results in lowered interfacial tension, finer and stabilized phase morphologies. The characteristics of different compatibilizing agents were compared for several of the blend systems. We also look at the influences of compatibilizing agents on mechanical properties of the blend systems. Some compatibilizing agents are able to produce substantial improvements in ultimate properties.     

Thermoplastic polyurethanes from renewable resources: effect of soft segment chemical structure and molecular weight on morphology and final properties

The effect of soft segment molecular weight and chemical structure on the morphology and final properties of segmented thermoplastic polyurethanes containing various hard segment contents has been investigated from the viewpoint of the degree of microphase separation. Vegetable oil‐based polyesters and corn sugar‐based chain extender have been used as renewable resources. The synthesis has been carried out in bulk without catalyst using a two‐step polymerization process. Physicochemical, thermal and mechanical properties, and also morphology, have been studied using Fourier transform infrared spectroscopy, differential scanning calorimetry, dynamic mechanical analysis, atomic force microscopy, X‐ray diffraction and mechanical testing. Chemical structure and molecular weight of polyols strongly affect the properties of the synthesized segmented thermoplastic polyurethanes. An increase in soft segment molecular weight leads to an increase of the degree of soft segment crystallinity and microphase separation, thus giving enhanced mechanical properties and higher thermal stability. Copyright © 2012 Society of Chemical Industry     

Effect of C5 petroleum resin content on damping behavior,morphology, and mechanical properties of BIIR/BR vulcanizates

In this work, the white‐silica‐filled vulcanizates of brombutyl rubber (BIIR)/cis 1,4 polybutadiene rubbers (BR) with hydrogenated aromatic hydrocarbon (C5) petroleum resins were prepared by compression molding, and the effects of C5 petroleum resin content on the damping behaviors and mechanical properties of BIIR/BR vulcanizates were investigated by foam force rheometer, dynamic mechanical analysis (DMA), scanning electron microscopy, and mechanical measurements. The results of this study showed that, the C5 resins could retard the vulcanization, and reduce the crosslink density and Mooney viscosity of vulcanizates. The DMA curves exhibited two independent peaks of loss factor (tanδ) corresponding to the glass transition of BR and BIIR vulcanizates, respectively. The addition of C5 resin had a positive impact on the damping of BIIR/BR vulcanizates, with the increment content of C5 resin, the main tanδ peaks shifted significantly to higher temperature and the effective damping temperature range was broadened remarkably, especially in the range of the BIIR glass transition. The mechanical properties such as tensile strength and abrasion performance were influenced by the C5 resin and the changes in mechanical properties were mainly due to the decline of crosslink density and the improvement of filler dispersion. © 2013 Wiley Periodicals, Inc. J. Appl. Polym. Sci., 2013     

Influence of fuel on phase formation,morphology, electric and dielectric properties of iron oxides obtained by SCS method

Nanopowders of iron oxides were obtained by Solution Combustion Synthesis (SCS) method from sol-gel compositions containing iron nitrates and soluble organic reducing agents (glycine, urea, citric acid). The synthesis processes and their intensity depending on the type of fuel and fuel/oxidizer ratio (?) were investigated. It was established that the combustion regime affects the phase formation of the obtained powders, their morphology, the color of the final Fe₂O₃ powders, dielectric properties and etc. It was shown that iron oxides with a preferred morphology and high dielectric properties (ε = 44.5 at ? = 0.6 vs ε = 4.0 at ? = 1.4 using urea as fuel) could be produced by the SCS method.     

Thermoplastic polyurethane/polypropylene blends based on novel vane extruder: A study of morphology and mechanical properties

Thermoplastic polyurethane (TPU) polypropylene (PP) blends of different weight ratios were prepared with a self‐made vane extruder (VE), which generates global dynamic elongational flow, and a traditional twin‐screw extruder (TSE), which generates shear flow. The mechanical properties, phase morphology, thermal behavior, and spherulite size of the blends were investigated to compare the different processing techniques. Samples prepared with a VE had superior mechanical properties than the samples prepared with a TSE. Scanning emission micrographs show that the fiber morphology of the TPU/PP blends (<60 wt% TPU) was improved by elongational flow in VE. Differential scanning calorimetry curves indicate that a dynamical elongational flow could improve the miscibility of the TPU/PP blends. The U‐shaped spherulite size curve indicates the changes in the spherulite size, as observed from a polarization microscope. Interlocked spherulites also reveal the apparent partial miscibility of the TPU/PP blends under elongational flow. POLYM. ENG. SCI., 54:716–724, 2014. © 2013 Society of Plastics Engineers     

Thermoplastic olefin/clay nanocomposites: Morphology and mechanical properties

Thermoplastic olefin (TPO)/clay nanocomposites were made with clay loadings of 0.6–6.7 wt %. The morphology of these TPO/clay nanocomposites was investigated with atomic force microscopy, transmission electron microscopy (TEM), and X‐ray diffraction. The ethylene–propylene rubber (EPR) particle morphology in the TPO underwent progressive particle breakup and decreased in particle size as the clay loading increased from 0.6 to 5.6 wt %. TEM micrographs showed that the clay platelets preferentially segregated to the rubber–particle interface. The breakup of the EPR particles was suspected to be due to the increasing melt viscosity observed as the clay loading increased or to the accompanying chemical modifiers of the clay, acting as interfacial agents and reducing the interfacial tension with a concomitant reduction in the particle size. The flexural modulus of the injection moldings increased monotonically as the clay loading increased. The unnotched (Izod) impact strength was substantially increased or maintained, whereas the notched (Izod) impact strength decreased modestly as the clay loading increased. © 2004 Wiley Periodicals, Inc. J Appl Polym Sci 92: 928–936, 2004     

Improved mechanical properties of ATBN-toughened epoxy networks by controlling the phase separation scale

Amine-terminated butadiene acrylonitrile (ATBN) rubber-toughened epoxy networks with different phase separation scale were formulated by adjusting acrylonitrile content in ATBN, and the effect of phase separation on stress–strain behavior, impact strength, dynamic mechanical thermal properties and thermo-gravimetric performance of the toughened epoxy networks were studied in detail. Scanning electron microscope analysis demonstrated that phase separation occurred in the toughened networks, forming a two-phase morphology, and the size of rubber particles was highly dependent on the acrylonitrile content in ATBN. Toughened epoxy network with larger phase separation scale exhibited longer ultimate elongation, and smaller phase separation scale was proved to be more effective in improving impact strength. Furthermore, bimodal rubber-particle distributed epoxy networks were obtained by addition of two types of ATBN simultaneously. The impact strength of the bimodal rubber-particle distributed epoxy network showed a great increase of 47% without sacrificing other mechanical properties, as compared to those of unimodal rubber-particle distributed epoxy networks.     

Physico‐mechanical,dynamic mechanical,and swelling properties of sodium chloride filled chlorobutyl vulcanizates

The effect of addition of rigid, nonreinforcing, and noninteracting filler viz. finely ground NaCl in chlorobutyl vulcanizates on properties such as physicomechanical, dynamic mechanical, and swelling has been studied. The nonreinforcing effect of NaCl in the system was studied by Russel and Cunnenn analysis and Kraus plots. Mechanical measurements of stress and strain at the break of filled and unfilled samples showed no appreciable change in the mechanical behavior of the system. The dynamic mechanical analysis showed that there is no change at all in the glass transition temperature with addition of NaCl filler. The damping properties showed an increase with increase in filler loading because of the filler–filler friction. The swelling behavior of NaCl‐filled CIIR was studied for a period of 60 days in four different solvents of varying chemical energy potential viz. water, chloroform, acetone, and tetrahydrofuran (THF). The degree of swelling was found to increase continuously with time in water, which is a good solvent for the filler, and in THF, which is a good solvent for the polymer matrix. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 102: 707–714, 2006     

Thermoplastic vulcanizates based on poly(methyl methacrylate)/epoxidized natural rubber blends: Mechanical,thermal, and morphological properties

Epoxidized natural rubbers (ENRs) with epoxide levels of 10, 20, 30, 40 and 50 mol % were prepared. The ENRs were later used to prepare thermoplastic vulcanizates (TPVs) by blending them with poly(methyl methacrylate) (PMMA) using various formulations. Dynamic vulcanization, using sulfur as a vulcanizing agent, was performed during the mixing process. The mixing torque increased as the ENR contents and epoxide molar percentage increased. This was because of an increasing chemical interaction between the polar groups of the blend components, particularly at the interface between the elastomeric and thermoplastic phases. The ultimate tensile strength of the TPVs with ENR‐20 was high because of strain‐induced crystallization. ENRs with epoxide levels >30 mol % exhibited an increase of tensile strength because of increasing levels of chemical interaction between the molecules and the different phases. The hardness of the TPVs also increased with increased epoxide levels but decreased with increased contents of ENRs. Two morphology phases with small domains of vulcanized ENR particles dispersed in the PMMA matrix were observed from scanning electron microscopy micrographs. The TPVs based on ENR‐20 and ENR‐50 showed smaller dispersed rubber domains than those of the other types of ENRs. Furthermore, the size of the vulcanized rubber domain decreased with increasing amounts of PMMA in the blends. The decomposition temperature of the TPVs also increased as both the levels of ENRs in the blends and the epoxide molar percentage increased. © 2005 Wiley Periodicals, Inc. J Appl Polym Sci 98: 1251–1261, 2005     

Thermal,mechanical, and structural properties of zno/polyethylene membranes made by thermally induced phase separation method

In this study, ZnO/polyethylene membranes were fabricated via thermally induced phase separation method. A set of tests including FE‐SEM, EDX, XRD, DSC, TGA, DMA, mechanical test, and pure water flux (PWF) for characterization of membranes were carried out. The results of EDX, XRD, and TGA analyses confirmed the presence of ZnO nanoparticles in the polymer matrix. The results of DSC analysis revealed that the melting point as well as the crystallinity of the membranes increased slightly with increasing ZnO content. However, glass transition temperature of the membranes was not affected by presence of the particles. Addition of nanoparticles also increased storage modulus, loss modulus. and tensile at break of the membranes due to the stiffness improvement effect of inorganic ZnO. Finally, it was observed that incorporation of the nanoparticles improved PWF of the membranes, whereas humic acid rejection decreased due to the increase in mean pore radius of membranes. © 2015 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2015 , 132, 42338.     

A survey of the rheological properties,phase morphology,and crystallization behavior of PP-POSS materials with weak phase separation

Polypropylene (PP) compounds with varying amounts (0.4-8.2 vol%) of tailored allyl-isobutyl polyhedral oligomeric silsesquioxane (POSS) were prepared by melt-blending. The dependence of the crystallization behavior and crystalline structure of PP on the melt-state phase morphology of PP-POSS materials is addressed. PP-POSS systems were predicted to exhibit weak phase separation in both the molten and solid states based on Bagley plot using Hansen solubility parameters. Small-amplitude shear rheometry analysis suggested that the highest loaded (8.2 vol%) PP-POSS system behaves as a two-liquid emulsion, whereas the low-content POSS (0.4-4.0 vol%) systems deviate from this model, resembling a polymer nanocomposite. Based on these findings we hypothesized the formation of a heterogeneous phase morphology in the molten state comprised of nano-size “pseudo-solid” POSS clusters and micrometer-size “pseudo-liquid” POSS droplets dispersed within the PP matrix, depending on the POSS content. Upon cooling, POSS droplets comingle, forming cube-like micrometer-sized crystal domains. The nonisothermal crystallization of PP is enhanced by the presence of POSS clusters. Small-angle X-ray scattering analysis revealed the formation of thinner and more heterogeneous folded chain PP lamellae in the PP-POSS systems.     

Effects of compounding procedure on morphology development,melt rheology,and mechanical properties of nanoclay reinforced dynamically vulcanized EPDM/polypropylene thermoplastic vulcanizates

New nanocomposite thermoplastic vulcanizates (TPVs) comprising dynamically cross‐linked nanoscale EPDM rubber particles dispersed throughout the polypropylene (PP) matrix have been prepared by both batch and continuous melt blending of PP with EPDM in the presence of vulcanizing ingredients, nanoclay and maleated EPDM (EPDM‐g‐MA) as compatibilizer. X‐ray diffraction, linear melt viscoelastic measurement, and tensile mechanical behavior results revealed that the developed microstructure is strongly affected by the type of the melt compounding process as well as the route of material feeding. When EPDM phase was precompounded with a vulcanizing agent, nanoclay, and EPDM‐g‐MA prior to the melt blending with PP, not only nanosize cross‐linked rubber particles appeared uniformly throughout the PP continuous phase, but also the melt blending leads to the significant enhancement of the mechanical properties compared with counterpart samples prepared by one‐step melt mixing process. Also better dispersion of nano layers in the rubber compound before melt blending with PP results in higher mechanical properties of the resulted TPV. POLYM. ENG. SCI., 56:914–921, 2016. © 2016 Society of Plastics Engineers     

Vulcanizates of epoxidized trans-polyisoprene: morphology,mechanical and dynamic properties

Morphology, curing characteristics, mechanical and dynamic properties of vulcanization of epoxidized trans-polyisoprene (ETPI) with different epoxy content were investigated. From scanning electron microscopy micrographs, it is observed that ETPI vulcanizates were a two-phase system. DSC shows that the residual crystallization reduced with increasing epoxy content. With increasing epoxy content, the induction period of cure shortened gradually as well as tensile strength, elongation at break, hardness and tear strength decreased. It is important to note that the wear resistance increased gradually with the increasing of epoxy content. Rebound values at 23 and 70 °C decreased which indicate that damping capacity and wet resistance performance increased, but the rolling resistance increased. DMA tests further show that wet resistance performance enhanced, damping capacity improved, but rolling resistance increased with increasing epoxy content of ETPI.     

Microstructure and mechanical properties of hydroxyapatite obtained by gel-casting process

In the present work, well-shaped HAp green bodies were obtained by the gel-casting process with 50 vol.% slurry. After drying, the microstructure and pore distribution of the green body were investigated. The density, compressive strength and flexural strength of the green body were 1.621 g/cm³, 32.6 ± 3.2 MPa and 13.8 ± 1.0 MPa, respectively. After pressureless sintering at the range of 1100–1300 °C for 2 h, the relative density of the final product ranges from 71.8 to 97.1% th. The maximum value of flexural strength, elastic modulus, hardness and fracture toughness were 84.6 ± 12.6 MPa, 138 ± 7 GPa, 4.45 ± 0.18 GPa and 0.95 ± 0.13 MPa m^1/2, respectively. SEM images show a compact and uniform microstructure; the average grain size was found by using the linear intercept method. XRD and FTIR determined the phase and the radical preserved after sintering.     

Melt processed PLA/PCL blends: Effect of processing method on phase structure,morphology, and mechanical properties

Poly(lactic acid) (PLA)‐rich poly(lactic acid)/poly(ε‐caprolactone) (PLA/PCL) blends were melt‐blended at different compositions. The compositions such as 90/10 and 80/20 were obtained using three different blending methods and processed by injection molding and hot pressing. All blends were immiscible. The crystallinity of PLA increased slightly in the presence of poly(ε‐caprolactone) (PCL), and the PCL exhibited fractionated crystallization in the presence of PLA. Injection molded specimens, compared with hot pressed specimens, presented much smaller PCL particles regardless of the blending method used. Some interfacial adhesion was observed in all cases. The stiffness of PLA/PCL blends decreased as the PCL content was increased and was independent of processing. Injection molded specimens showed ductile behavior and broke at elongation values close to 140%, while the elongation at break of the hot pressed specimens was clearly lower, most likely due to the larger size of the PCL particles. Although the impact strength of the blends remained low, it improved by approximately 200% with 30% PCL and by 350% with 40% PCL. © 2015 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2015 , 132, 42641.     

Thermoplastic film adhesives based on phenol-functional acrylic copolymers: synthesis,mechanical and adhesion properties

Acrylic polymers possessing varying proportions of pendant phenol groups were synthesized by the free radical copolymerization of N-(4-hydroxyphenyl) maleimide (HPM) with butyl acrylate (BuA) and acrylonitrile (AN) and characterized. These thermoplastics form excellent films and their mechanical and adhesion properties were evaluated as a function of the phenol content. Enhancing the HPM content increased both the tensile strength and the modulus but decreased the elongation. A nominal increase in the phenol content was found to be conducive for improving the adhesion properties of the films. At higher concentrations, the adhesion properties showed a decreasing trend due to the embrittlement caused by the rigid maleimide groups. The adhesion property at 50°C increased linearly with the HPM content due to an increased T _g, whereas a reverse trend was observed for the adhesion property measured at-196°C, due to the dominance of the embrittlement effect. The reduced flow characteristics of the high HPM-loaded systems led to a diminished honeycomb flat-wise tensile strength. Enhancing the HPM concentration in the chain promoted the adhesion properties for the vulcanization bonding of nitrile rubber to aluminium. Addition of silica filler marginally improved the lap shear strength (LSS) for the metal-metal system, but was detrimental for rubber-metal bonding; a reverse trend was observed for the carbon-filled system. The diminished performance for metal-metal bonding by carbon could be attributed to the weakening of the interphase, whereas the enhanced rubber-metal bonding could be due to possible reinforcement of the rubber phase by carbon. The fillers generally improved the high temperature adhesion. However, they impaired the flow properties of the resin and, thereby, adversely affected the flat-wise tensile strength in both cases.     

Thermoplastic polyvinyl alcohol/multiwalled carbon nanotube composites: Preparation,mechanical properties,thermal properties,and electromagnetic shielding effectiveness

This study uses the solution mixing method to combine plasticized polyvinyl alcohol (PVA) as a matrix, and multiwalled carbon nanotubes (MWCNTs) as reinforcement to form PVA/MWCNTs films. The films are then laminated and hot pressed to create PVA/MWCNTs composites. The control group of PVA/MWCNTs composites is made by incorporating the melt compounding method. Diverse properties of PVA/MWCNTs composites are then evaluated. For the experimental group, the incorporation of MWCNTs improves the glass transition temperature (T_g), crystallization temperature, T_c), and thermal stability of the composites. In addition, the test results indicate that composites containing 1.5 wt % of MWCNTs have the maximum tensile strength of 51.1 MPa, whereas composites containing 2 wt % MWCNTs have the optimal electrical conductivity of 2.4 S/cm, and electromagnetic shielding effectiveness (EMI SE) of ?31.41 dB. This study proves that the solution mixing method outperforms the melt compounding method in terms of mechanical properties, dispersion, melting and crystallization behaviors, thermal stability, and EMI SE. © 2016 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2016 , 133, 43474.