Mechanical properties and blend compatibility of natural rubber –chlorosulfonated polyethylene blends

Natural rubber (NR) was blended with chlorosulfonated polyethylene (CSM) with various formulation and blend ratios (NR/CSM: 80/20 –20/80, wt/wt). Rubber blends were prepared by using a two‐roll mill and vulcanized in a compression mold to obtain the 2 mm‐thick sheets. Tensile properties, tear resistance, thermal aging resistance, ozone resistance, and oil resistance were determined according to ASTM. Compatible NR/CSM blends are derived from certain blends containing 20–30% CSM without adding any compatibilizing agent. Tensile and tear strength of NR‐rich blends for certain formulations show positive deviation from the rule of mixture. Thermal aging resistance depends on formulation and blend ratio, while ozone and oil resistance of the blends increase with CSM content. Homogenizing agents used were Stuktol®60NS and Epoxyprene®25. Stuktol®60NS tends to decrease the mechanical properties of the blends and shows no significant effect on blend morphology. Addition of 5–10 phr of epoxidized natural rubber (ENR, Epoxyprene® 25) increases tensile strength, thermal aging resistance, and ozone resistance of the blends. It is found that ENR acts as a compatibilizer of the NR/CSM blends by decreasing both CSM particle size diameter and α transition temperature of CSM. © 2005 Wiley Periodicals, Inc. J Appl Polym Sci 99: 127–140, 2006     

Photoluminescence study of β relaxation of polyethylene blends

Secondary β relaxation of polyethylene blends (50/50 HDPE/LDPE) were studied by photoluminescence of anthracene molecules dissolved in the polymer bulk. The temperature of the β relaxation has been determined as T_β = ?40°C by the dependence of the ratio of vibronic components of the fluorescence band on the temperature. The molecular mechanism of this relaxation has been discussed considering the possibility of the energy migration involving anthracene molecules in the singlet electronic excited and ground states. © 1993 John Wiley & Sons, Inc.     

TGA analysis of γ‐irradiated linear low‐density polyethylene

Linear low‐density polyethylene (LLDPE), based on butene‐1 or hexene‐1, was irradiated with γ‐rays under vacuum or in the presence of air. The study focused on the influence of the dose rate and the γ‐dose on the thermal properties of LLDPE. Differential scanning calorimetry, thermogravimetric analysis (TGA), and TGA/FTIR techniques were used to address the thermal behavior as a result of γ‐irradiation. During this irradiation, competition between crosslinking and scission reactions, subsequent to oxidation reactions, occurred in the polymeric material, which strongly depends on the experimental conditions. A decrease of the crystallinity for γ‐irradiated samples was observed in particular for samples irradiated under vacuum. This observation may be explained by increased hindrance of segment mobility due to crosslinking reactions that prevent crystal growth. TGA investigations revealed an enhancement of the thermal stability for samples irradiated under vacuum but not for those irradiated in air. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 100: 2790–2795, 2006     

Preparation and characterization of γ‐irradiated crosslinked silicone rubber/organoattapulgite composites

Silicone rubber (SR)/organoattapulgite (OAT) composites were prepared with γ‐irradiation crosslinking at a dose range varied from 30 to 300 kGy. Natural fibrillar silicate attapulgite (AT) was modified by silane coupling agent, and the obtained OAT was used as reinforcing fillers in SR. The effect of irradiation doses on the degree of crosslinking of SR/OAT composites was determined by solvent swelling method. It was found that the molecular weight between crosslinks (M_c) reduced with the increase in irradiation doses. Moreover, the addition of OAT to SR matrix promoted an increase in the crosslinking density of the composites because of the presence of the active crosslinking sites of OAT. The mechanical properties of the SR/OAT composites including tensile strength, elongation at break, and Shore A hardness subjected to various irradiation doses were studied. The experimental results showed that the tensile strength, elongation at break, and Shore A hardness were all improved significantly in the presence of OAT, which indicated that OAT was an alternative reinforcing filler of SR. In addition, the effect of various irradiation doses on the mechanical properties of SR and SR/OAT composites was also investigated. POLYM. COMPOS., 2010. © 2009 Society of Plastics Engineers     

Tensile properties of polyethylene blends

Binary and ternary blends were prepared from low, medium, and high density polyethylene. The tensile properties of these materials indicated that the blends formed either compatible or semi-compatible mixtures. One of the ternary blends exhibited a slight synergism in properties which could be partially attributed to an enhancement in crystallinity. Such blends may have practical utility by yielding materials having a combination of strength, stiffness, and toughness.     

Development of novel elastomeric blends containing natural rubber and ultra-low-density polyethylene

This study sought to develop novel elastomeric compounds using natural rubber (NR) and ultra-low-density polyethylene (ULDPE). Blends were prepared by means of a two-roll mill for three ratios (70/30, 60/40, and 50/50 NR/ULDPE). Conventional vulcanization was performed in a compression mold. The physical and mechanical properties of the blend were determined according to ASTM standards. The results were compared with those obtained from NR blended with styrene-butadiene rubber (SBR). The morphological examinations with scanning electron microscopy indicated that ULDPE was compatible with NR; thus, the addition of a compatibilizer was not necessary. The cocontinuous phase was dominant in the NR/ULDPE blend containing 50 and 60 wt % NR. The tensile properties, tear resistance, and aging resistance of the NR/ULDPE blends were found to be superior to those of NR/SBR blends. On the other hand, the abrasion and flex cracking resistances of the NR/ULDPE blend were inferior to those exhibited by SBR blends but the Mooney viscosity and resilience of both blends fell in the same range. However, the addition of dicumyl peroxide appeared to have caused crosslinking of the ULDPE phase in the blend, which in turn increased the tensile properties and abrasion and aging resistance. The properties of the tertiary NR/SBR/ULDPE blend were investigated as well. © 2001 John Wiley & Sons, Inc. J Appl Polym Sci 82: 650–660, 2001     

Short fiber-reinforced thermoplastic elastomers from blends of natural rubber and polyethylene

Thermoplastic elastomer blends of natural rubber (NR) with high density polyethylene (HDPE) and with low density polyethylene (LDPE) were reinforced with short silk fiber. Processing characteristics such as torque and temperature developed during mixing and the effect of processing parameters such as nip gap and number of passes in the mill necessary to secure maximum orientation of the fibers in the blends were studied. A small nip gap and a single pass in the mill were found to give best results. Of the different mixing sequences studied, the sequence where short fibers followed by rubber were added to the molten thermoplastic was found to give a uniform dispersion of fibers. Fiber breakage and the change in aspect ratio of the fibers after mixing were also examined. It was observed that, as a direct consequence of the mixing sequence, each fiber was coated with a layer of thermoplastic. Although the properties improved on the addition of the dry bonding system of silica–resorcinol–hexamethylenetetramine, the comparatively long curing time required for full development of adhesion between the fibers and the matrix proved to be a major disadvantage associated with the incorporation of the bonding system. The tensile and tear properties were substantially enhanced, but the ultimate elongation decreased sharply with increasing loading of short fibers in the blends. The effect of fiber orientation and the development of anisotropy in the properties was also noted. Scanning electron microscopy (SEM) studies of the benzene-extracted surfaces of the NR/HDPE (high density polyethylene) blends substantiated the theory of fibers behaving like “mechanical anchors” between the rubber and thermoplastic phase. The effect of fiber loading on the tear and tensile properties of the blends of NR/LDPE with varying blend ratios was studied. Most pronounced improvement in the properties on the addition of short fibers was observed in the high rubber blends. As the plastic content in the blends increased, the short fibers were found to have a lesser influence on the properties. SEM photomicrographs of the tensile and tear fracture surfaces indicated the fiber orientations and the effect of orientation, fiber loading, and blend ratios on the nature of fracture.     

Electrical and thermal properties of γ‐irradiated nitrile rubber/rice husk ash composites

The effects of both the rice husk ash (RHA) loading and fumed silica (FS) loading on the structure, thermal stability, and electrical properties of acrylonitrile–butadiene rubber (NBR) composites were studied. The filler loading were chosen to be 5 and 20 phr for RHA and 5 and 30 phr for silica. Also, the effect of the γ‐irradiation dose (25 kGy) on these parameters was investigated. The structure and thermal stability were studied with X‐ray diffraction and thermogravimetric analysis techniques. Furthermore, some electrical parameters, such as the direct‐current electrical conductivity (σ_dc), activation energy (E_a), dielectric constant (?′), and dielectric loss (?″), were determined. The incorporation of both RHA and FS resulted in improved thermal stability after γ irradiation at 25 kGy. The loading of FS on NBR was shown to decrease σ_dc, ?′, and ?″ and increase E_a. On the other hand, the loading of RHA showed the opposite trend. Finally, γ irradiation of NBR composites filled with both fillers decreased the values of σ_dc, ?′, and ?″ for all the samples, which followed the trend for the unirradiated composites. © 2009 Wiley Periodicals, Inc. J Appl Polym Sci, 2010     

Tensile properties and interfacial adhesion of silicone rubber/polyethylene blends by reactive blending

Two‐phase blends of silicone rubber (SR) and linear low density polyethylene (LLDPE) were prepared by reactive blending using peroxide crosslinking agent of SR. The tensile strength and elastic modulus of the SR were found to be increased by reactive blending with LLDPE without sacrifice of the elongation. The improvement of the tensile properties is attributed to the strong adhesion at the interface between SR matrix and LLDPE domain due to the chemical reaction by peroxide. The observation by polarized optical microscopies revealed that the debonding did not occur at the interface, but the LLDPE domains were elongated to longer one. Despite the elongation of the LLDPE domain, the blends exhibited good deformation recoverability. © 2018 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2018 , 135, 46192.     

Carboxymethylation of γ‐irradiated starch

Low viscosity carboxymethyl corn starch was prepared by the reaction of γ‐irradiated starch with monochloroacetic acid in the presence of alkali. It was found that irradiation dose influences the product viscosity remarkably. The viscosity decreases as the irradiation dose level increases; however, the viscosity increases with the increasing dose rate and the degree of substitution (DS). γ‐Irradiation can activate the starch to react with monochloroacetic acid, and the more of the irradiation dose, the higher of the DS and the reaction efficiency. The product has the character of low viscosity at high concentration, and the more of the irradiation dose, the more similar of the rheological behavior to a Newtonian liquid. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 101: 2210–2215, 2006     

Influence of thermal and morphological characteristics on mechanical responses of polypropylene/γ‐irradiated elastomer blends

The approach of this paper is to examine the mechanical responses of polypropylene (PP)/γ‐irradiated ethylene acrylic elastomer blends and subsequently compare them with the PP/unirradiated ethylene acrylic elastomer blends. Thorough correlations were drawn between the mechanical characteristics of blends and their morphological, thermal, thermomechanical, and fractured surface morphological aspects. The idea of carrying out γ‐irradiation was to introduce crosslinking points in the elastomer phase. For better understanding, correlations between the impact test results and the fractured surface morphologies were analyzed. The limited tensile properties of PP/γ‐irradiated elastomer blends were attributed not only to the poor interfacial adhesion, obtained by fitting with several theoretical mechanical models, but also to the substantially higher elastomer particle size in the blends than in the PP/unirradiated elastomer blends. The higher loss modulus and tan δ values for PP/unirradiated elastomer blends along with the attainment of much smaller particles of elastomers were responsible for the phenomenal increase in impact properties, which was actually attributed to the formation of crazes inside the dispersed phase during applied impact stress. © 2018 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2018 , 135, 46597.     

HIPS/γ‐irradiated UHMWPE/carbon black blends: Structuring and enhancement of mechanical properties

CB‐containing HIPS/UHMWPE and HIPS/XL‐UHMWPE are unique systems, in which structuring takes place, affecting the electrical (to be described in a future article), rheological, mechanical, and dynamical‐mechanical properties. The XL‐UHMWPE particles have undergone structural fixation due to the crosslinking, maintaining their porosity and internal intricate structure even after high‐temperature melt processing, as opposed to the UHMWPE particles. Differences in the flow mechanisms of HIPS/UHMWPE and HIPS/XL‐UHMWPE blends have been attributed to polymer viscous flow in the former case vs. particle slippage in the latter. The mechanical properties of HIPS/UHMWPE are enhanced when utilizing XL‐UHMWPE as a dispersed phase, especially the strength, because of changes in the inherent properties of the UHMWPE following irradiation, and in particular, the nature of the HIPS/XL‐UHMWPE interface. The results for the CB‐containing 70HIPS/30XL‐UHMWPE blend are especially surprising and of practical importance, due to the fact that no degradation of the mechanical properties has occurred as a result of the CB incorporation. The dynamical mechanical properties reflect the differences between the UHMWPE and XL‐UHMWPE‐containing blends as well. The presence of either type of UHMWPE, CB content, and blend composition affect the dissipation, but have only a minor influence on the transition temperatures of the components. Of special interest is the increased damping of XL‐UHMWPE–containing compositions. © 1999 John Wiley & Sons, Inc. J Appl Polym Sci 74: 1731–1744, 1999     

Thermomechanical devulcanization of ethylene propylene diene monomer rubber and its application in blends with high-density polyethylene

The recycling of ethylene propylene diene monomer (EPDM) rubber remains a challenge, as its cross-linked structure cannot be broken down reversibly. Devulcanization may offer a breakthrough; however, a 100% decrease in cross-link density (CLD) with no chain degradation has never been reported. In this research, sulfur- and peroxide-cured EPDM rubbers of known compositions were devulcanized on a two-roll mill and in an internal mixer. The CLD of both rubber samples decreased by around 85%, while the sol content of the peroxidic devulcanizate was considerably higher than that of the sulfuric devulcanizate (23% vs. 3%). Horikx's theory revealed that sulfur-cured samples showed excellent selectivity for cross-link scission, while peroxide-cured samples suffered degradation. Uncured, cured, and devulcanized rubber samples were mixed into high-density polyethylene at various compositions. Large EPDM rubber contents impaired the mechanical properties of the blends, indicating insufficient adhesion between the two phases. Compounds containing originally uncured rubber mixtures had the most beneficial mechanical properties.     

Search for the sources of color in thermally aged,weathered and γ-ray irradiated bisphenol a polycarbonate

Bisphenol A polycarbonate (BPA-PC) is an important high performance engineering thermoplastic well known for its outstanding combination of toughness, transparency and heat resistance. These properties make it an idel material for demanding applications where it is exposed to external stresses such as elevated temperatures, ultraviolet light and γ-ray sterilization. However, on extended exposure to these conditions, BPA-PC slowly degrades, turning progressively more yellow, eventually leading to a decrease in its physical properties. Over the years, there has been numerous studies made to understand these degradative processes so as to better design more stable BPA-PC formulations. In this paper, this chemistry is briefly reviewed along with more recent work in this area with a special emphasis on the efforts made to identifying the actual chemical species responsible for the observed yellow color and the chemistry responsible for their formation.     

Acrylic acid γ-ray irradiation-grafted nylon 4 membranes

This study was to improve the performances of nylon 4 membranes for washing waste-water treatment of nuclear power plants, e.g., removal of detergent and salt by membranes. The effects of the degree of grafting and ionization on the reverse osmosis performances of acrylic acid (AA)-grafted nylon 4 membranes by γ-ray irradiation modification were investigated. The relationships of operating conditions, such as feed concentrations of salt and detergent, operating temperature, and pressure, and the performances of water flux and solute rejection of the prepared membranes were obtained. Water flux of the prepared membranes was highly sensitive with the operating temperature. It was found that an increase in the operating pressure could increase the water flux and the impaction effect directly. Water flux and salt rejection were significantly improved by both ionized and nonionized AA-grafted nylon 4 membranes compared to ungrafted nylon 4 membranes. Water flux increased rapidly and solute rejection dropped off slightly as the grafted membranes were ionized. The 100% detergent rejection could be obtained by the nonionized AA-grafted nylon 4 membranes with 38.6 and 69.6% degrees of grafting under various operating conditions. Results obtained showed that these modified nylon 4 membranes were usable for washing waste-water treatment of nuclear power plants. © 1993 John Wiley & Sons, Inc.     

Mechanical and flow properties of high-density polyethylene/low-density polyethylene blends

The recycling of plastic waste is of particular interest in large urban areas where municipal waste represents a large ecological problem. To achieve their objective (consumer products from plastic waste), formulators of a recycling program have to understand the implications of working with mixtures of different resins. Furthermore, in a multiphase system, the thermomechanical history experienced by the resins during processing represents an important link between operating conditions, resin properties, and final product performance. High-density polyethylene/low-density polyethylene (HDPE/LDPE) blends (10, 20, 35, 50, 65, 80, and 90 percent by weight HDPE) were melt blended in an internal mixer. A complete rheological characterization was performed on each blend. The resulting blends were extruded under different processing conditions. The extruded sheets were further characterized to determine their mechanical properties, The experimental results show important differences in the mechanical properties (transverse and longitudinal) of the sheets obtained from the blends. These differences are explained on the basis of the processing conditions (thermomechanical history) and the rheological properties of the molten blends.     

Morphology and tensile properties of high-density polyethylene/natural rubber/thermoplastic tapioca starch blends: The effect of citric acid-modified tapioca starch

The effect of citric acid on the tensile properties of high density polyethylene (HDPE)/natural rubber (NR)/thermoplastic tapioca starch (TPS) blends was investigated. The ratio between HDPE/NR was fixed at 70/30 and used as the matrix system. TPS loadings, after modification with citric acid (TPSCA) and without modification (TPS), were varied from 0 to 30 wt %. The morphologies and tensile properties of HDPE/NR blends were evaluated as a function of TPS loadings. The tensile strength, Young's modulus, and elongation at break were found to decrease with increasing TPS loading. However, a slight improvement in the tensile strength of HDPE/NR/TPSCA blends at 5 and 10 wt % TPS loadings were observed. TPS can be partly depolymerised to produce a low viscosity product when processed with citric acid. TPS with low viscosity can easily disperse in the thermoplastic natural rubber (TPNR) system and reduce the surface tension at the interphase of TPS-HDPE/NR as shown by scanning electron microscopy (SEM). © 2011 Wiley Periodicals, Inc. J Appl Polym Sci, 2012     

Performance of crystallization analysis fractionation and preparative fractionation on the characterization of γ‐irradiated low‐density polyethylene

The effects of γ‐radiation on a low‐density polyethylene (LDPE) were investigated by novel techniques, such as crystallization analysis fractionation and preparative fractionation, to analyze and compare their performance with other analytical procedures such as DSC, FTIR, and GPC. The LDPE was thus irradiated with four different doses of γ‐radiation. Different fractions were obtained from these irradiated materials by preparative fractionation, which were characterized by the above‐mentioned analysis techniques. The changes in the morphology and chemical structure of LDPE after the irradiation were analyzed and it was found that both oxidative scission and crosslinking are phenomena related to the exposure of LDPE at high‐energy radiation. Crystallization analysis fractionation and preparative fractionation proved to be suitable techniques to characterize the effects of γ‐radiation on a low‐density polyethylene material. © 2004 Wiley Periodicals, Inc. J Appl Polym Sci 94: 1803–1814, 2004     

Linear low-density polyethylene/high-density polyethylene blends: Effect of high-density polyethylene content on die swell and flow instability

This work aimed to evaluate the effect of high-density polyethylene (HDPE) content and of shear rate on the die swell and flow instability of linear low-density polyethylene (LLDPE)/HDPE blends. The results showed that the die swell of the LLDPE/HDPE blends increased with the increase in the shear rate. At high shear rates, the increase in the HDPE content led to an increase in the die swell of LLDPE/HDPE blends. The surface morphology analysis of the extrudates by optical and scanning electron microscopy revealed the presence of sharkskin and stick–slip flow instabilities in LLDPE and LLDPE/HDPE blends at the shear rates investigated. These instabilities were attenuated with the addition of HDPE and almost disappeared in the LLDPE/HDPE blend containing 50 wt% of HDPE.     

Rheological properties of recycled chlorinated polyethylene/natural rubber blends vulcanized by sulfur

Blends of elastomeric chlorinated polyethylene (CPE) and natural rubber (NR) with a blend composition ratio of 80/20 were prepared and recycled. Viscoelastic properties of the blends as a function of the recycling cycle were monitored. The results obtained revealed that, with an increase in the number of recycling cycles, a noticeable change in the viscoelastic properties of blends could be observed; that is, a decrease in the elastic contribution associated with a noticeable shift in the glass‐transition temperature of the NR phase of the blends was observed, implying a molecular change in the NR phase via a thermal chain‐scission mechanism. The influence of magnesium oxide (MgO) as an acid acceptor for CPE on the viscoelasticity of the blends was also investigated. Through a reduction of the amount of MgO, the molecular change was found to be more pronounced in NR than in CPE phases in a manner similar to the increase in the recycling cycles. An explanation of the changes in the viscoelastic properties of the blends with various MgO loadings and recycling cycles is proposed in terms of thermal degradation via a molecular chain‐scission mechanism taking place mainly in the NR phase. © 2008 Wiley Periodicals, Inc. J Appl Polym Sci, 2009