Use of EVA-containing mercapto groups in natural rubber–EVA blends. I. Mechanical,thermal, and morphological properties

The effect of ethylene–vinyl acetate (EVA) modified with mercaptoacetic acid on mechanical, thermal, and morphological properties of blends of natural rubber (NR) and EVA copolymers has been investigated. The introduction of EVASH promotes a crosslinking of natural rubber phase as indicated by extraction experiments and microscopy analysis. This crosslinking may be attributed to bonding between sulfhydryl groups along the EVASH backbone and double bonds in rubber phase and may be responsible for the hardness improvement of most of the studied blends. Better results on hardness and ultimate tensile strength with EVASH addition were achieved for NR–EVA (60 : 40) ratio, probably due to cocontinuous morphology of this composition. The influence of EVASH on crystallinity degree of NR–EVA blends was also studied by differential scanning calorimetry. The morphology of the blends was studied through scanning electronic microscopy. © 1995 John Wiley & Sons, Inc.     

The effect of peroxide crosslinking on thermal,mechanical, and rheological properties of polycaprolactone/epoxidized natural rubber blends

Polycaprolactone (PCL)/epoxidized natural rubber (ENR) blends (PCL/ENR = 70/30, 50/50 wt/wt) were prepared by a melt mixing in an internal mixer in the presence of a small amount (0.5 and 1 phr) of dicumyl peroxide. The effect of peroxide crosslinking on thermal, mechanical, and rheological properties of the blends was investigated by means of DSC, tensile test, and small amplitude oscillating rheometer, respectively. It was revealed that peroxide crosslinking enhanced degree of crystallinity of PCL phase and its non-isothermal melt crystallization temperature. The crosslinked blends behave like a thermoplastic elastomer exhibiting high elongation-at-break and fairly good elastic recovery as well as melt processibility. From melt rheological analysis, the peroxide crosslinked blends showed more pronounced shear thinning effect and higher elasticity compared to simple blends.     

Studies on mechanical and thermal properties of ternary blends of polyethylenes. I

Six film samples of varying compositions of linear low‐density polyethylene (LLDPE), 10–35 wt %, and high‐density polyethylene (HDPE), 40–65 wt %, having a fixed percentage of low‐density polyethylene (LDPE) at 25 wt % were extruded by melt blending in a single‐screw extruder (L/D ratio = 20 : 1) of uniform thickness of 2 mil. The tensile strength, elongation at break, and impact strength were found to increase up to 60 wt % HDPE addition, starting from 40 wt % HDPE, in the blends and then decreased. The blend sample B‐500 was found to be more thermally stable than its counterparts. The appearance of a single peak beyond 45 wt % HDPE content in the blend in dynamic DSC scans showed the formation of miscible blend systems and this was further confirmed by scanning electron microscopic analysis. © 2005 Wiley Periodicals, Inc. J Appl Polym Sci 96: 1691–1698, 2005     

Selective crosslinking in polymer blends. II. Its effect on impact strength and other mechanical properties of polypropylene/unsaturated elastomer blends

The effect of selective crosslinking of the unsaturated elastomer particles in polypropylene (PP) matrix was investigated. The crosslink system comprised N,N′-m-phenylene-bismaleimide and 6-ethoxy-2,2,4-trimethyl-1,2-dihydroqinoline or polymerized-(2,2,4-trimethyl-1,2-dihydroquinoline). The system, which produces only carbon radicals, crosslinks the elastomer particles selectively without causing excessive degradation of the PP matrix. The reaction was carried out under a dynamic crosslinking process using a twin extruder on PP/EPDM, PP/SBS, and PP/SIS blends, all of which comprised 80 wt % of PP and 20 wt % of the elastomer. After the crosslinking, the impact strength of the blends increased. Especially remarkable increase is obtained at 23°C where PP is above its T_g. The increase of interfacial adhesion caused by production of PP/elastomer graft copolymer at the interface is considered to be the most important factor in the improvement. It permits the interactions of the stress concentrate zone developed at the elastomer particles and causes shear yielding of the PP matrix. Impact fracture energy absorption can be thus changed by adjusting the degree of the interfacial adhesion even at essentially the same morphology. The crosslinked elastomer particles also play the role of a nucleation agent. The selective cross-linking of the elastomer particles in PP/elastomer blends is demonstrated to be an excellent technique to produce a high-impact, high-modulus PP. © 1994 John Wiley & Sons, Inc.     

The effect of kevlar fiber reinforcement on the curing,thermal, and dynamic‐mechanical properties of an epoxy/anhydride system

Curing, thermal, and dynamic‐mechanical relaxational behavior of an epoxy/‐anhydride resin and a Kevlar‐fiber/epoxy composite were compared. Reinforcement by Kevlar fibers had a catalytic effect on the curing reaction. Reinforced formulations produced higher extents of reaction than neat formulations at the same curing time. Curing kinetics was also studied by means of DSC heating scans. When the Kevlar content increased, the heat flow curves and the exothermic peak temperature shifted significantly to lower temperatures. The glass transition temperature of the matrix also decreased as the Kevlar content increased. Postcuring reduced the differences between the neat and reinforced formulations. Loss tangent and storage modulus versus frequency master curves were obtained from isothermal dynamic‐mechanical measurements. The effect of fiber addition on the main dynamic‐mechanical relaxation was analyzed with a simple mechanical model.     

Dependence of mechanical properties in polyolefin blends on shear and thermal history

Variously dispersed two-component blends of linear polyethylene and a thermoplastic rubber were subjected to different thermal histories after compression molding and their properties were evaluated. It has been shown that ultimate properties of the blends are not defined by the composition, but vary greatly with degree of dispersion and thermal history. Stronger materials failing in a ductile manner were produced under shock cool conditions and in, finely-dispersed blends. Brittle failures and weaker materials were favored by annealing procedures and in blends subjected to brief and/or lowshear dispersion procedures. Time and temperature dependent changes in properties of blends prepared under standard conditions have been observed and activation energies for the aging process calculated. Data interpretation was based on a hypothesis of domain morphology in the blends, and on the existence of “tie molecules” which help to determine the cohesive strength of domain boundaries.     

Effect of different curing systems on heat shrinkability and mechanical properties of ethylene vinyl acetate/epoxidized natural rubber blends

Ethylene vinyl acetate (EVA)/epoxidized natural rubber (ENR) blends containing 10 and 30 wt % ENR were prepared by using an internal mixer. Five different types of curing systems were employed: dicumyl peroxide (DCP), sulfur (S), phenolic resin (Ph), DCP + S, and DCP + Ph. DCP could crosslink with both EVA and ENR while S and Ph were curing agents for ENR. The DCP system provided the lowest tensile properties and tear strength because of low crosslinking in ENR phase. Addition of sulfur or phenolic resin increased the mechanical properties due to a better vulcanization of the rubber phase. The mechanical properties of the blends decreased with increasing ENR content. The rubber particle size in the blends containing 30% ENR played a more important role in the mechanical properties than the blends containing 10% ENR. ENR particle size did not affect heat shrinkability of EVA and a well vulcanized rubber phase was not required for high heat shrinkage. Furthermore, heat shrinkage of the blends slightly changed as the ENR content increased for all curing systems. With regard to the mechanical properties and heat shrinkability, the most appropriate curing system was DCP + Ph and in the case the 10 wt % ENR content produced a more favorable blend. © 2010 Wiley Periodicals, Inc. J Appl Polym Sci, 2011     

Studies on the thermal and curing behavior of polyimide blends

Blends of thermosetting (Thermid MC-600 and Thermid FA-700) and thermoplastic (UL-TEM 1000) polyimide resins with different compositions were prepared. Curing and thermal behavior of the blends were investigated using differential scanning calorimetry and dynamic thermogravimetry in a nitrogen atmosphere. The peak exotherm temperature increased with increasing amount of thermoplastic resin, whereas the heat of polymerization decreased. The electrical characteristics of the blends were also investigated using a dielectric analyzer. Dynamic as well as isothermal scans were recorded. Ionic conductivity, permittivity, and the loss factor were measured as a function of temperature at various frequencies. These results showed the complete curing of the resins having 50% Ultem at 225°C in 1 h, whereas Thermid MC-600 required a postcuring step to observe fully cured resins. A marginal decrease in thermal stability was observed on blending. © 1994 John Wiley & Sons, Inc.     

Effect of conductive polyaniline in thermoplastic natural rubber blends on the mechanical,thermal stability,and electrical conductivity properties

This research was conducted to fabricate thermoplastic natural rubber/polyaniline (TPNR/PANI) blends via melt blending method using an internal mixer and followed by compression molding. The effects of PANI contents between 1 and 5 wt % PANI in the TPNR blends on the mechanical properties, thermal stability, electrical conductivity (impedance), and morphology observation were investigated. The TPNR/3 wt % PANI sample exhibited the highest tensile strength (3.7 MPa), elongation at break (583%), flexural strength (1.8 MPa), flexural modulus (37.0 MPa), and impact strength (7.1 kJ m⁻²). From the aspect of thermal properties, it was found that with the addition of PANI, the thermal stability of the TPNR/PANI increased. Comparing to nonconductive TPNR sample, the incorporation of PANI promoted the electrical conductivity characteristic to PANI-filled TPNR blends which showing a magnitude order of 10⁻⁹ S cm⁻¹. Scanning electron microscopy micrograph revealed the good distribution of PANI at the optimum content (3 wt % PANI) in the TPNR blends and the good interaction between TPNR and PANI. It can be concluded that the TPNR blends incorporated with a low loading of PANI could be a newly good conductive material. © 2019 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2019 , 136, 47527.     

The effect of curing additive on the mechanical properties of phthalonitrile-carbon fiber composites

Unidirectional carbon fiber-reinforced phthalonitrile composite panels were fabricated by prepreg consolidation with bis[4-(4-aminophenoxy)phenyl]sulfone (p-BAPS) as the phthalonitrile curing additive. Rheometric measurements and elevated-temperature, short beam shear tests were used to evaluate the cure of the composite as a function of the cure and postcure conditions. These techniques revealed that a fully cured phthalonitrile composite was obtained when the composite was heated at 375°C for 8 hours. Room-temperature mechanical properties of the cured composite were then evaluated using short beam shear, tension, and flexural tests. The results are compared with those obtained by curing the phthalonitrile with 1,3-bis(3-aminophenoxy)benzene (m-APB). The data indicate that substitution of p-BAPS for m-APB has little effect on the mechanical properties of the cured composite. Elevated-temperature, short beam shear studies up to 371°C show that the cured phthalonitrile composite retains approximately 70% of its room-temperature apparent interlaminar shear strength. The composite also retains 70% of its room-temperature storage modulus up to 450°C. Polym. Compos. 25:554–561, 2004. © 2004 Society of Plastics Engineers.     

The effect of composition on the dynamic and mechanical properties of natural rubber–poly(methylmethacrylate) blends

The miscibility of the components in natural rubber–poly(methylmethacrylate) blends for potential use as reinforced rubbers was evaluated using the glass transition temperatures, peak widths of the loss tangent peak at the glass transition and the complex heat capacity data obtained from dynamic mechanical thermal analysis (DMTA), and modulated differential scanning calorimetry (MDSC). In addition, the effect of the poly(methylmethacrylate) content on the dynamic mechanical and the physical properties such as tensile behavior and hysteresis loss was studied. DMTA and MDSC data clearly indicated that the blends were phase‐separated. Nevertheless, the glass transition temperature of the natural rubber component in the 30–50 wt % NR/PMMA blends has shifted to higher temperatures compared to the natural rubber treated under the same condition, indicating some limited extent of mixing of components in these blends. The physicomechanical properties including moduli at 100, 300, and 500% and tensile strength of the NR/PMMA blends were determined. Incorporation of PMMA into NR matrix improved the strength properties of the NR/PMMA blends prepared reasonably akin to interpenetrating polymer networks (IPN) polymerization method. © 2009 Wiley Periodicals, Inc. J Appl Polym Sci, 2009     

Curing behavior and thermal mechanical properties of cyanate ester blends

Cyanate esters are a class of important thermally resistant polymers. To tailor their processability and thermomechanical properties, a series of cyanate ester blends based on a trifunctional novolac cyanate ester (HF‐5), a difunctional bisphenol E cyanate ester (HF‐9), and a reactive catalyst [2,2′‐diallyl bisphenol A (DBA)] were formulated. The effect of the blend composition on the rheology and curing behavior of these cyanate ester blends and the corresponding thermal and mechanical properties of the cured cyanate ester blends was studied. The results showed that HF‐5 contributed to good mechanical property retention at high temperatures because of its trifunctionality, whereas HF‐9 imparted processability by reducing the viscosity and extending the pot life of the formulated cyanate ester blends at the processing temperature. On the basis of the results, an optimal cyanate ester blend suitable for resin transfer molding was determined: the HF‐5/HF‐9/DBA weight ratio of 80 : 15 : 5 exhibited good processability and thermomechanical properties. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 102: 4284–4290, 2006     

Effects of reactive functional groups in the compatibilizer on mechanical properties of compatibilized blends

The compatibility of blends of polyamide-6/[styrene-(ethylene-butylene)-styrene] triblock copolymer (SEBS) was enhanced with a compatibilizer, maleated SEBS, whose compositions were varied from 0 to 4 wt % of the blends. The maleated SEBS (MA-g-SEBS) was synthesized by reacting (grafting) maleic anhydride (MA) with SEBS in the laboratory at various maleic anhydride concentrations ranging from 8 to 13 wt % of the maleated compatibilizer. The effects of graft levels of the reactive MA functional group in the compatibilizer on the effectiveness in compatibilizing the blends were investigated. The morphology and the impact strengths of the compatibilized blends were determined. It was found that, depending on the maleated extents, the compatibilizer influenced significantly the properties of the blends. Although the maleated extents (graft ratios) of the compatibilizer is influential, the concentrations of the compatibilizer in the blends more sensitively affected the mechanical properties of the compatibilized blends. In summary, this study has shown that by increasing the MA contents (within the reported window) in the compatibilizer, the impact toughness could be more dramatically improved. © 1994 John Wiley & Sons, Inc.     

The effects of polyamic acid on curing behavior,thermal stability,and mechanical properties of epoxy/DDS system

A thermoplastic modification method was studied for the purpose of improving the toughness and heat resistance and decreasing the curing temperature of the cured epoxy/4, 4′‐diaminodiphenyl sulfone resin system. A polyimide precursor‐polyamic acid (PAA) was used as the modifier which can react with epoxy. The effects of PAA on curing temperature, thermal stability and mechanical properties were investigated. The initial curing temperature (T_i) of the resin with 5 wt % PAA decreased about 50°C. The onset temperature of thermal decomposition and 10 wt %‐weight‐loss temperature for the resin system containing 2 wt % PAA increased about 60°C and 15°C respectively. Besides, the value of impact toughness and plain strain fracture toughness for the modified epoxy resin increased ～ 190% and 55%, respectively. Those changes were attributed to the outstanding thermal and mechanical properties of polyimide, and more importantly to formation of semi‐interpenetrating polymer networks composed by the epoxy network and linear PAA. © 2012 Wiley Periodicals, Inc. J. Appl. Polym. Sci., 2013     

LLDPE/LDPE blends. I. Rheological,thermal, and mechanical properties

Structure and mechanical properties were studied for the binary blends of a linear low density polyethylene (LLDPE) (ethylene‐1‐hexene copolymer; density = 900 kg m⁻³) with narrow short chain branching distribution and a low density polyethylene (LDPE) which is characterized by the long chain branches. It was found by the rheological measurements that the LLDPE and the LDPE are miscible in the molten state. The steady‐state rheological properties of the blends can be predicted using oscillatory shear moduli. Furthermore, the crystallization temperature of LDPE is higher than that of the LLDPE and is found to act as a nucleating agent for the crystallization of the LLDPE. Consequently, the melting temperature, degree of crystallinity, and hardness of the blend increase rapidly with increases in the LDPE content in the blend, even though the amount of the LDPE in the blend is small. © 1999 John Wiley & Sons, Inc. J Appl Polym Sci 74: 3153–3159, 1999     

Cure characteristics and mechanical properties of hydrogenated natural rubber/natural rubber blends

The cure characteristics and mechanical properties of blends consisting of hydrogenated natural rubber (HNR) and natural rubber (NR) blends were investigated. The HNR/NR blends at 50/50 wt ratio were vulcanized using various cure systems: peroxide vulcanization, conventional vulcanization with peroxide, and efficient vulcanization with peroxide. The HNR/NR vulcanizates cured by the combination of peroxide and sulfur donor (tetramethylthiuram disulfide, TMTD) in the efficient vulcanization with peroxide exhibited the best mechanical properties. It was also found that the hydrogenation level of HNR did not affect the tensile strength of the vulcanizates. The tensile strength of the blends decreased with increasing HNR content because of the higher incompatibility to cause the noncoherency behavior between NR and HNR. However, the HNR/NR vulcanizate at 50/50 wt ratio showed the maximum ultimate elongation corresponding to a co‐continuous morphology as attested to by scanning electron micrographs. © 2008 Wiley Periodicals, Inc. J Appl Polym Sci, 2009     

The impact of polymer matrix blends on thermal and mechanical properties of boron nitride composites

To improve mechanical and thermal properties of a hexagonal boron nitride platelet filled polymer composites, maleic anhydride was studied as a coupling agent and compatibilizer. Injection molded blends of acrylonitrile butadiene styrene (ABS), high-density polyethylene (HDPE), and maleic anhydride with boron nitride filler were tested for thermal conductivity and impact strength to determine whether adding maleic anhydride improved interfacial interactions between matrix and filler and between the polymers. Adding both HDPE and maleic anhydride to ABS as the matrix of the composite resulted in a 40% improvement in impact strength without a decrease in thermal conductivity when compared to an ABS matrix. The best combination of thermal conductivity and impact strength was using pure HDPE as the matrix material. The effective medium theory model is used to help explain how strong filler alignment helps achieve high thermal conductivity, greater than 5 W/m K for 60 wt % boron nitride. © 2019 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2019 , 137, 48661.     

The effect of poly(butylene succinate) content on the structure and thermal and mechanical properties of its blends with polylactide

Poly(butylene succinate) (PBS) and polylactide (PLA) were blended in a co‐rotating twin‐screw extruder with various contents of PBS from 0 to 100 wt%. The effect of PBS content on the thermal and mechanical properties of PBS/PLA blends was investigated by using DSC, softening point measurements, a Charpy impact test and tensile testing. The Fourier transform infrared spectra showed that the polymers are immiscible, but the addition of PBS could modify the PLA structure in PBS/PLA blends by changing the content of amorphous and crystalline phases. In addition, the cold crystallization temperature of PLA in blends decreases in comparison with pure PLA, which shows that PBS could have a plasticizing effect on PLA. This is confirmed by the results of DSC analysis. The mechanical properties of the blends depend on the percentage of PBS addition. Typically, the mechanical properties of PBS/PLA blends are intermediate between the properties of the polyesters from which they are obtained. However, in some cases unexpected changes in mechanical properties of the blends were observed. For example, the elongation at break for a PBS/PLA blend containing 10 wt% PLA is higher than for pure PBS. © 2019 Society of Chemical Industry     

The effect of UV‐irradiation and molten medium on the mechanical and thermal properties of polystyrene–polycarbonate blends

Polymer materials with improved properties can be obtained through polymer blends. As a polymer mixture is generally immiscible and incompatible, it is necessary to develop new methods to improve the interfacial adhesion. The aim of this work is to find formulations and associated processes to upgrade engineering polystyrene (PS) and polycarbonate (PC) polymer blends with the objective of using the best “process‐formulation” couple. In this study, blends of PS/PC were prepared in molten medium using reactive extrusion after UV‐irradiation. The effects of UV‐irradiation on some properties of blends under molten medium were investigated by differential scanning calorimetry (DSC), fourier transform infrared (FTIR), and thermogravimetric analysis (TGA). The data showed that the presence of polycarbonate in the blend increased the tensile strength and elongation at break with respect to pure PS. The mechanical properties of the blends were improved after irradiation. All irradiated blends are thermally more stable than those nonirradiated. Chemical changes can be clearly seen in FTIR spectra through two bands assigned to C?O and OH groups. The mutual influence between the PS/PC polymer blends compositions during UV‐irradiation was studied. PS and PC have different photo‐mechanisms due to the larger UV absorption of polystyrene and formation of more stable tertiary carbon radicals. © 2011 Wiley Periodicals, Inc. J Appl Polym Sci, 2012     

Effect of maleimide curing on mechanical properties of ground tyre rubber/waste polypropylene blends

Abstract

Blends of ground tyre rubber and waste polypropylene with a maleimide curing system (50∶50 blends of ground tyre rubber/waste polypropylene) were prepared in a Haake Rheocord Polylab System, at 180°C and 90 rev min^–1 for 5 min. The curing agent and the activator used were N,N′-meta-phenylene dimaleimide (HVA-2) and di(tert-butylperoxyisopropyl) benzene (DTBPIB) respectively. The HVA-2 level varied from 0 to 5 parts per hundred parts (pphp), while the DTBPIB level varied from 0 to 1 pphp. Melt viscosity, tensile strength and elongation at break showed an increase with HVA-2 content, while the impact energy showed an optimum at 3 pphp level. The addition of the DTBPIB increased melt viscosity further and produced a homogeneous phase morphology of the blends. Impact energy improved with the DTBPIB level, while elongation at break and tensile strength showed an optimum at 0·6 pphp. Swelling behaviour and gel/sol from the boiled xylene extractions were studied, and the results obtained were correlated with the impact and tensile properties.