Wiley

Multi‐walled carbon nanotube/polypropylene composites (PPCNs) were prepared by melt compounding. The linear viscoelastic properties, nonisothermal crystallization behavior, and kinetics of PPCNs were, respectively, investigated by the parallel plate rheometer, differential scanning calorimeter (DSC), X‐ray diffractometer (XRD), and polarized optical microscope (POM). PPCNs show the typical nonterminal viscoelastic response because of the percolation of nanotubes. The rheological percolation threshold of about 2 wt % is determined using Cole‐Cole method. Small addition of nanotube can highly promote crystallization of PP matrix because of the heterogeneous nucleating effect. With increasing nanotube loadings, however, the crystallization rate decreases gradually because the mobility of PP chain is restrained by the presence of nanotube, especially at high loading levels. © 2008 Wiley Periodicals, Inc. J Appl Polym Sci 2008

Polycarbonates (PCs) are commonly used as a blend and a composite to achieve pecuniary advantages and dimensional stability. While the toughness of a homogeneous PC matrix has been extensively investigated, examination for the toughness of heterogeneous blend systems such as PC/polypropylene (PP) blends has been limited. Furthermore, recent interest in highly flowable PCs (low‐molecular‐weight PCs with low ductility) has surfaced due to the large and geometrically complex plastic parts. Herein, the toughness for PC/PP blends and PC/PP/talc composites in a ductile and a brittle PC matrix was explored by using various toughness measurements such as notched Izod impact strength, falling dart impact, boss quasi‐static energy/impact energy, and tensile toughness tests. In a ductile PC matrix [melt flow index (MFI) = 8], the incorporation of PP gradually reduced the toughness. On the other hand, the toughness was improved by 450% at 2 wt % PP in a brittle PC matrix (MFI = 19). Similarly, in the talc‐induced brittle PC matrix, the toughness was enhanced at the PP loading from 2 to 10 wt %. The density of PC/PP blends was gradually reduced from 1.19 to 1.10 g cm⁻³ with increasing PP concentration from 0 to 20 wt %. Degradation, density, thermal behaviors, and morphology were also investigated. © 2018 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2019, 136, 47110.

The thermal sensitivity, nucleating ability, and nonisothermal crystallization of high‐density polyethylene (HDPE) with different wood fillers during wood/HDPE melt processing were investigated with thermogravimetric analysis and differential scanning calorimetry. The results showed that the wood degraded at a lower temperature than HDPE. The thermal decomposition behavior was similar across wood species. The most remarkable dissimilarities were observed between wood and bark in the decomposition rate around a processing temperature of 300°C and in the peak temperature location for cellulose degradation. The higher degradation rate for bark was explained by the devolatilization of extractives and the degradation of lignin, which were present in higher amounts in pine bark. The nucleating ability for various wood fillers was evaluated with the crystalline weight fraction, crystal conversion, crystallization half‐time, and crystallization temperature of the HDPE matrix. The nucleation activity improved with the addition of wood particles to the HDPE matrix. However, no effect of wood species on the crystal conversion was found. For composites based on semicrystalline matrix polymers, the crystal conversion may be an important factor in determining the stiffness and fracture behavior. © 2009 Wiley Periodicals, Inc. J Appl Polym Sci, 2009

The influence of the electron beam modification of a dual‐phase filler on the dynamic mechanical properties of styrene‐butadiene rubber (SBR) is investigated in the presence and absence of trimethylol propane triacrylate or triethoxysilylpropyltetrasulfide. Electron beam modification of the filler results in reduction of the tan δ at 70°C, a parameter for rolling resistance, and an increase in the tan δ at 0°C, a parameter for wet skid resistance of SBR vulcanizates. These modified fillers give significantly better overall performance in comparison with the control dual‐phase filler. This variation in properties is explained in terms of filler parameters such as the filler structure that leads to rubber occlusion and filler networking. These results are further corroborated using the master curves obtained by the time–temperature superposition principle. © 2003 Wiley Periodicals, Inc. J Appl Polym Sci 88: 2992–3004, 2003

Simple blending of natural rubber/ethylene–propylene–diene rubber (NR/EPDM) generally results in inferior mechanical properties because of curative migration and their differences for filler affinity. In this work, the 70/30 and 50/50 NR/EPDM blends prepared by reactive processing techniques were investigated and compared with the simple, nonreactive blends. The reactive blend compounds were prepared by preheating EPDM, containing all curatives to a predetermined time related to their scorch time prior to blending with NR. For the 70/30 gum blends, four types of accelerators were studied: 2,2‐mercaptobenzothiazole (MBT), 2,2‐dithiobis‐ (benzothiazole) (MBTS), N‐cyclohexyl‐2‐benzothiazolesulfenamide (CBS), and N‐tert‐butyl‐2‐benzothiazolesulfenamide (TBBS). When compared with the simple blends, the reactive blends cured with CBS and MBTS showed a clearly improved tensile strength whereas the increase of tensile strength in the blends cured with TBBS and MBT was marginal. However, a dramatic improvement of ultimate tensile properties in the reactive 50/50 NR/EPDM blends cured with TBBS was observed when compared with the simple blend. For the N‐550‐filled blends at the blend ratios of 70/30 and 50/50, the reactive‐filled blends prepared under the optimized preheating times demonstrated superior tensile strength and elongation at break over the simple blends. The improved crosslink and/or filler distribution between the two rubber phases in the reactive blends accounts for such improvement in their mechanical properties. This is shown in the scanning electron micrographs of the tensile fractured surfaces of the reactive blends, which indicate a more homogeneous blend. © 2008 Wiley Periodicals, Inc. J Appl Polym Sci, 2009

Filled covulcanizates of elastomer blend comprising natural rubber (NR) and ethylene‐propylene‐diene rubber (EPDM) of commercial importance were successfully prepared by using a multifunctional rubber additive; namely, bis(diisopropyl)thiophosphoryl disulfide (DIPDIS). A Two‐stage vulcanization technique further improved the physicochemical properties of the blend vulcanizates by restricting, through the formation of polar rubber bound intermediates, the migration of curative and filler from lower to highly unsaturated rubber. Scanning electron microscopy studies indicate homogeneity and coherency in the morphology of the two‐stage vulcanizates. © 2002 Wiley Periodicals, Inc. J Appl Polym Sci 84: 1001–1010, 2002; DOI 10.1002/app.10361

Electron‐beam initiated crosslinking of a poly(vinyl chloride)/epoxidized natural rubber blend (PVC/ENR), which contained trimethylolpropane triacrylate (TMPTA), was carried out over a range of irradiation doses (20–200 kGy) and concentrations of TMPTA (1–5 phr). The gelation dose was determined by a method proposed by Charlesby. It was evident from the gelation dose, resilience, hysteresis, glass‐transition temperature (T_g), IR spectroscopy, and scanning electron microscopy studies that the miscible PVC/ENR blend underwent crosslinking by electron‐beam irradiation. The acceleration of crosslinking by the TMPTA was further confirmed in this study. Agreement of the results with a theory relating the T_g with the distance between crosslinks provided further evidence of irradiation‐induced crosslinking. The possible mechanism of crosslinking induced by the irradiation between PVC and ENR is also proposed. © 2001 John Wiley & Sons, Inc. J Appl Polym Sci 81: 1914–1925, 2001

Films were prepared from a blend of low‐density polyethylene (LDPE) and ethylene‐vinyl acetate (EVA) containing 45% VA and ditrimethylol propane tetraacrylate (DTMPTA). Electron‐beam initiated crosslinking of these films was carried out over a range of radiation doses (20–500 kGy), concentrations of DTMPTA (1–5 parts by weight), and blend compositions. The IR studies revealed that oxidation and crosslinking dominated up to an irradiation dose of 100 kGy. At higher irradiation doses chain scission and disproportionation predominated among all the competitive processes for the 50:50 blend without DTMPTA. The gel fraction of the films increased with the increase in irradiation dose, DTMPTA level, and EVA content of the blends. X‐ray diffraction and differential scanning calorimetry studies showed that the crystalline portion of the blends was only affected by radiation at higher irradiation doses (≥200 kGy). Scanning electron microscopy studies indicated that in the 50:50 blend the LDPE formed the continuous phase, which was further confirmed by atomic force microscopy and transmission electron microscopy studies. However, a co‐continuous morphology was formed when the EVA content was increased. When DTMPTA was added to the blends (≥3 wt %), the 50:50 blend exhibited a co‐continuous morphology. © 2001 John Wiley & Sons, Inc. J Appl Polym Sci 81: 1936–1950, 2001

EPDM incorporated into blends of natural rubber/butadiene rubber (NR/BR) improves ozone resistance. In this work, the inferior mechanical properties of NR/BR/EPDM blends generally obtained by conventional straight mixing are overcome by utilizing a reactive processing technique. The entire amount of curatives, based on a commonly employed accelerator N‐cyclohexyl‐2‐benzothiazole sulfenamide (CBS) and sulfur, is first added into the EPDM phase. After a thermal pretreatment step tuned to the scorch time of the EPDM phase, the modified EPDM is mixed with premasticated NR/BR. The reactive blend vulcanizates show a significant improvement in tensile properties: tensile strength and elongation at break, as compared to those prepared by straight mixing, in both gum and carbon black‐filled blends. The increase of tensile properties in gum and filled reactive blend vulcanizates does suggest that the reactive processing technique leads to more homogeneous blends due to, either a better crosslink distribution, or more homogeneous filler distribution, or both. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 103:2538–2546, 2007

The internal structure of pressure‐sensitive adhesives was studied using electron microscopy and measurements of mechanical loss, tensile modulus, viscosity, stress relaxation, and critical surface tension. The adhesives were blends of natural rubber and the pentaerythritol ester of hydrogenated rosin. Compositions containing up to 40 wt‐% resin are homogeneous mixtures. The temperature dispersion of mechanical loss shows a single peak, and the peak value remains almost constant. When the resin concentration exceeds 40 wt‐%, phase separation occurs. The disperse phase is resin containing a small amount of rubber. Two peaks, or a peak and a shoulder, appear in the temperature–loss peak curves. It is postulated that one of the peaks corresponds to the phase in which resin is uniformly dispersed in the rubber and the other peak corresponds to the resin phase which contains a small amount of rubber. Evidence for homogeneity in compositions containing 40 wt‐% or less resin and of heterogeneity at higher concentrations of resin was also obtained from the electron microscope observations. The relationships between the internal structure of pressure‐sensitive adhesives and viscosity, Young's modulus, the relaxation spectrum, tack, and critical surface tension are discussed.