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The main objective of this study is to develop wood adhesives that can be cured at room temperature, based on modified natural rubber (NR) latex. Two types of modified NR, namely poly(acetoacetoxyethyl methacrylate)-grafted NR, NR-g-PAAEM, and poly(acetoacetoxyethyl methacrylate-co-methyl methacrylate)-grafted NR, NR-g-P(AAEM-co-MMA), were synthesized. Emulsion polymerization technique was exploited to synthesize the graft copolymers. The hydrophilicity of NR after grafting modifications was examined by means of contact angle. These results reveal that the NR become more hydrophilic after being modified with poly(acetoacetoxyethyl methacrylate), PAAEM, and/or poly(methyl methacrylate), PMMA. Adhesion properties in terms of lap shear strength were studied for wood adhesives derived from both types of NR graft copolymers, with glutaraldehyde (GTA) as the crosslinking agent. The results show that adhesives based on the NR graft copolymers gave higher lap shear strength than the NR latex adhesive. For the graft copolymers, the NR-g-P(AAEM-co-MMA) adhesive exhibited much higher lap shear strength than the NR-g-PAAEM adhesive. This indicates that the incorporation of PMMA chains into the NR-g-PAAEM molecules significantly increased the cohesive strength of the resulting adhesive, which is probably due to increased modulus and hardness of the adhesive film. POLYM. ENG. SCI., 2017. © 2017 Society of Plastics Engineers

The aim of the present study was to improve the compatibility in blends of natural rubber (NR) and polyamide 12 (PA12) by grafting NR with hydrophilic monomer, diacetone acrylamide (DAAM), via seeded emulsion polymerization. The increase in polarity of NR after grafting modification was confirmed by a considerable increase in the polar component of its surface energy. Blends of graft copolymers of NR and poly(diacetone acrylamide) prepared using 10 wt% of DAAM (NR-g-PDAAM10) and PA12 were prepared at a 60/40 blend ratio (wt%) using simple blend and dynamic vulcanization techniques. The mechanical and rheological properties of the resulting blends were subsequently investigated and compared with those of the corresponding blends based on unmodified NR. The results show that dynamic vulcanization led to a significant increase in both mechanical and rheological properties of the blends. It was also observed that the dynamically cured NR-g-PDAAM10/PA12 blend had smaller particle size of vulcanized rubber dispersed in the PA12 matrix than observed for the dynamically cured NR/PA12 blend. This is due to the compatibilizing effect of DAAM groups present in NR-g-PDAAM10 molecule, which decreases the interfacial tension between the two polymeric phases. Therefore, it can be stated that the interfacial adhesion between NR and PA12 was improved by the presence of DAAM groups in NR molecule. This was reflected in the higher tensile properties observed in the dynamically cured NR-g-PDAAM10/PA12 blend. Copyright © 2017 John Wiley & Sons, Ltd.

Carbon nanotube (CNT)-filled epoxidized natural rubber (ENR) composites were prepared by mixing in an internal mixer and thereafter on a two-roll mill. Silane coupling agent, namely 3-aminopropyltriethoxy silane (APTES), was directly incorporated in the ENR-CNT composites during mixing of rubber and CNTs in the mixer, to perform in situ functionalization. It was found that pre-crosslinking of ENR and APTES occurred especially at high APTES concentrations, such as 0.06 mL/(g of CNTs) and caused strong CNT agglomeration in the ENR matrix. However, the pre-crosslinking could be reduced or avoided by decreasing the APTES concentration. In the concentration range 0.01–0.015 mL/(g of CNTs) of APTES, the APTES molecules were grafted on the CNT surfaces and generated new chemical linkages with the ENR. This improved the CNT dispersion in the ENR matrix and enhanced the composite properties. A very low approximately 0.5 phr of CNT threshold concentration for electric percolation was achieved in this type of composites. Also, three-dimensional connected CNT networks were found to form in the ENR matrix at very low APTES levels. Thus, the electrical conductivity achieved in these composites reached the level required of conductive materials. POLYM. ENG. SCI., 57:381–391, 2017. © 2016 Society of Plastics Engineers

Conductive elastomer composite based on carbon black (CB) filled epoxidized natural rubber with 50 mol% epoxide (ENR-50) were prepared using two types of CB: high abrasion furnace (HAF) and extra conductive furnace (ECF) with different loading levels. It was found that the ENR-50/ECF composite had the maximum tensile strength at lower loading of 10 phr as compared with the ENR-50/HAF composite at 20 phr. Furthermore, the Kraus's relation revealed that two types of CB provide different degree of reinforcement. Incorporation of CB leads to increase permittivity, loss factor and conductivity of the composites. However, the ENR-50/ECF composites show higher conductivity than that of the ENR-50/HAF composites. The electrical percolation thresholds (pc) of ENR-50/HAF and ENR-50/ECF composites were observed at loading levels of CB = 12.0 and 6.3 vol%, respectively. These are very low percolation thresholds of the conductive elastomer composites with CB. POLYM. COMPOS., 2016. © 2016 Society of Plastics Engineers

Rice husk ash (RHA) and siliceous earth (SE) were compared as alternative reinforcing fillers in epoxidized natural rubber (ENR) vulcanizates. The effects of RHA and SE on processability, curing characteristics, mechanical, thermal and morphological properties, and thermoelastic behavior of vulcanizates were studied, in the presence and absence of bis(triethoxysilylpropyl) tetrasulfide (TESPT) silane coupling agent. The results indicated that the RHA offers processing advantages over the commercial SE. The filled ENR vulcanizates without TESPT provided higher tensile strengths than the unfilled ENR vulcanizates, but had lower elongations at break. This is attributed to physical interactions between filler particles and rubber matrix, which affects the reinforcement by the filler. The modification of filler surfaces with TESPT resulted in further improved properties of the rubber vulcanizates. This is attributed to the coupling of polymer matrix and filler particles via TESPT linkages that increased the polymer–filler interactions. It was also found that the RHA filler, a renewable resource, exhibited similar reinforcement to the conventional SE. This indicates that the RHA has great potential as a reinforcing filler that can substitute for conventional SE in polymer composites. POLYM. COMPOS., 2016. © 2016 Society of Plastics Engineers

Three different types of benzyl ester were synthesized from vegetable oils (i.e., coconut oil, palm oil, and soybean oil). They were then utilized in styrene butadiene rubber (SBR) compound reinforced with carbon black. First, the benzyl esters were investigated by varying the molar ratio of fatty acids in vegetable oil to benzyl alcohol, the catalyst concentration, the reaction time, and the reaction temperature, observing the yield of benzyl ester. Then SBR was compounded with the benzyl esters, observing cure characteristics, mechanical properties, and morphologies of the SBR compounds, with the control compound containing conventional aromatic oil. The highest 96% yield of benzyl ester was obtained with palm oil fatty acid. Furthermore, the benzyl ester oils consumed less energy during processing but gave comparable carbon black dispersion, in comparison with the conventional aromatic oil.

Composites of carbon nanotubes (CNT) and epoxidized natural rubber (ENR) were prepared by in-situ functionalization of CNT with two alternative silane coupling agents: bis(triethoxysilylpropyl) tetrasulfide (TESPT) and 3-aminopropyltriethoxysilane (APTES). The reactions of ENR molecules with the functional groups on CNT surfaces and with the silane molecules were characterized by Fourier transform infrared. Furthermore, cross-link density, relaxation behaviors, curing, mechanical, electrical, and morphological properties of pristine ENR and the ENR composites were investigated. Very low percolation thresholds, at CNT concentrations as low as 1 phr, were observed in the ENR–CNT and the ENR–CNT–TESPT composites. This might be attributed to improvements in the chemical linkages between ENR molecules and functional groups on CNT surfaces that led to a homogenous dispersion of CNTs in the ENR matrix, with loose CNT agglomerates. POLYM. ENG. SCI., 55:2500–2510, 2015. © 2015 Society of Plastics Engineers

Summary N-phenyl-p-phenylenediamine modified epoxidized palm oil (m-EPO) was synthesized and applied as an alternative processing oil in laboratory tests of rubber compounding. The effects of added functionalities in the chemical structure of m-EPO on the properties of ENR/PP TPVs were investigated. Palm oil (PO), epoxidized palm oil (EPO), and petroleum based white oil (WO) were used in this comparative study. The results show that oxirane rings and amine structures on N-phenyl-p-phenylenediamine promoted the compatibility of processing oil with ENR molecules, due to structural similarity and interactions between polar functional groups. Furthermore, the amine structures enhanced the formation of active sulfurating agent for sulfur vulcanization. Therefore, increased torque differences with shorter cure times were observed for ENR vulcanizates with m-EPO, relative to those of the TPVs with the other oils. Also, there were clear improvements in the tensile strength and the elongation at break stemming from the fine morphology of the vulcanized ENR particles. This indicates that the novel m-EPO processing oil is a competitive alternative for the rubber industry in terms of its technical performance.

Epoxidized natural rubbers (ENRs) with three different epoxide contents (i.e., 20, 35, and 50 mol% indicated as ENR20, ENR35, and ENR50, respectively) were prepared. They were then reinforced with 3-methyacryloxypropyl trimethoxysilane-modified nanosilica (MPTS-SiO2). Influence of epoxide level in ENR molecules on morphological, mechanical and dynamic mechanical properties of the ENR nanocomposites was investigated. The scanning electron microscopy results revealed larger agglomerates of SiO2 were found in the ENR composites with higher epoxide content. Furthermore, the strength and moduli of the ENR nanocomposites increased with increasing epoxide content. However, the optimal tensile strength and elongation at break were observed in the nanocomposites with the intermediate level of epoxide contents. The correlation between the strength properties and the interfacial silica-matrix adhesion indicated that the maximum interfacial adhesion of the nanocomposites was observed in the nanocomposite with ENR35. Also, DMA results indicated stronger interaction between ENR35 and MPTS-SiO2 due to higher storage modulus. POLYM. COMPOS., 2015. © 2015 Society of Plastics Engineers

The optimum condition of processing parameters (mixing temperature, rotor speed, fill factor, and blend ratio) and prediction models for the best key mechanical properties of ethylene propylene diene terpolymer/polypropylene thermoplastic vulcanizates (EPDM/PP TPVs) was investigated by using the Taguchi's optimization technique and data analysis. The results reveal that all of the processing parameters affected significantly the mechanical properties of the EPDM/PP TPVs, but specifically the blend ratio contributed more than 90% in effect size on tensile strength and tension set. There were three main factors, the mixing temperature, the fill factor, and the blend ratio, influencing the elongation at break. Furthermore, the mathematic models were effective and reliable in predicting the properties of TPVs. The correlation of mechanical properties, stress relaxation, and phase morphologies of the TPVs prepared from the predicted models was also investigated. It can be summarized that the morphological structure and stress relaxation of the TPVs were strongly governed by the EPDM content in the blend ratio. That is, the higher the EPDM content, the better phase morphology having smaller size of the vulcanized EPDM particles distributed in the PP matrix and the higher rate of stress relaxation. Moreover, these two properties were then principally pushing the mechanical characteristics of the EPDM/PP TPVs. Copyright © 2015 John Wiley & Sons, Ltd.

Sodium-montmorillonite nanoclay was modified with octadecylamine and compounded with natural rubber (NR) by dry mixing method. The effects of organoclay loading level on mechanical properties, thermal–mechanical behavior, and heat build-up of NR/organoclay nanocomposites were investigated. Temperature scanning stress relaxation technique was used to characterize the thermal–mechanical behavior of the composites. The morphological properties were assessed by X-ray diffraction and transmission electron microscopy. Loading levels of organoclay below 5 phr gave improved mechanical properties and heat build-up, along with exfoliated clay structure in the nanocomposites. On the other hand, with loading levels above 7 phr the organoclay tended to agglomerate, and X-ray diffraction revealed an intercalated structure. In these cases, the excess residual organoclay caused significantly increased stress relaxation and heat build-up. Unmodified sodium-montmorillonite as filler did not significantly affect the mechanical and heat build-up properties of NR vulcanizates. POLYM. COMPOS., 2014. © 2014 Society of Plastics Engineers

The objective of this study was to prepare natural rubber composites filled with carbon nanotubes (CNTs) that show an electrical percolation threshold at very low CNT concentrations. Therefore, two methods of surface functionalization of CNTs were investigated to enable an improved dispersion of CNTs and chemical interaction between CNTs and rubber matrix. On one hand, the CNTs have been functionalized ex situ by acid treatment and silanization reaction with bis(triethoxysilylpropyl) tetrasulfide before mixing with the rubber and otherwise in situ functionalization was directly carried out during the processing of the composites in the internal mixer. The grafting of silane molecules onto CNT surface was established by Fourier transform infrared spectroscopy and scanning electron microscopy. Tensile tests revealed the outstanding properties of composites prepared by in situ silanization method. The in situ silanization led to a better dispersion of the CNTs and the formation of chemical linkages between CNT surface and rubber and this became manifest in higher reinforcement of the rubber, higher crosslink densities, and a lower electrical percolation threshold. It was also shown that the in situ silanization is retarding the vulcanization reaction. POLYM. COMPOS., 36:2113–2122, 2015. © 2014 Society of Plastics Engineer

International audience; Flexible composites with a high electrical permittivity are pursued in materials research, due to their potential applications in electrical devices. We synthesized such ceramic-polymer composites from BaTiO3 and epoxidized natural rubber. The influence of BaTiO3 concentration on cure characteristics, mechanical (static & dynamic), dielectric, and morphological properties of the composites was investigated. The tensile strength and elongation at break decreased with BaTiO3 loading, while the storage modulus and permittivity of composites increased. As for dynamic electrical properties, the dielectric loss factor and tan delta of the composites showed a maximum peak within the frequency range extending up to 10(5) Hz, reflecting the relaxation process of the polymer matrix. All of the composites showed two peaks in the frequency dependence of electric modulus, due to conductivity and molecular relaxation. Scanning electron microscopy micrographs confirmed the 0-3 structure of composites, with isolated BaTiO3 particles.

Thermoplastic natural rubber nanocomposites based on epoxidized natural rubber (ENR) and polypropylene blends at a fixed blend ratio of 50/50 wt% reinforced with small amount (2.5 wt%) of nanosilica (SiO2) were prepared by melt-mixing through three different incorporation sequences in an internal mixer. The effects of incorporation techniques on morphology, crystallization behavior, mechanical properties, dynamic, rheological characteristics, and thermal resistance of thermoplastic natural rubber (TPNR) nanocomposites were investigated. It was found that the dispersion of nanosilica in TPNRs was significantly dependent on the incorporation sequence. In the case where SiO2 was premixed in ENR before blending with polypropylene (PP), the final morphology showed the good dispersion of SiO2 in ENR phase, while the SiO2 particles were localized near the PP interface when SiO2 was premixed the in PP first. Whereas, when the three components were simultaneously mixed, the SiO2 particles were mainly dispersed in the PP phase. It was also found that the improvements of Young's modulus, tensile strength, damping behavior, and thermal stability of TPNR nanocomposites were more pronounced when the SiO2 particles localized in ENR phase. By contrast, the presence of SiO2 particles in PP domain either near the interface or inside the PP phase affected the reduction in crystallinity of PP phase and showed a negative effect on mechanical properties due to the poor interface interaction between PP and SiO2 particles. POLYM. COMPOS., 33:1911–1920, 2012. © 2012 Society of Plastics Engineers

Natural rubber (NR)/thermoplastic polyurethane (TPU) blends were prepared with a dynamic vulcanization technique. The main objective was to prepare high-performance thermoplastic vulcanizates (TPVs) based on natural rubber [thermoplastic natural rubber (TPNR)] with low hardness values and improved thermal and mechanical properties. In this study, the preparation of dynamically cured NR/TPU blends was carried out systematically, and the final properties were compared to those of typical commercial TPVs. The influence of sulfur-cured systems, accelerator types, process parameters, and rubber types were investigated. The developed NR/TPU-based TPNRs showed better tensile strengths and thermal properties than commercial TPVs with similar hardnesses. Moreover, the epoxidized natural rubber (ENR)/TPU-based TPNRs exhibited a low compression set. The incorporation of NR into the TPU reduced the Shore A hardness to about 60 in comparison to a value of about 85 for the neat TPU; the blends also showed improved oil resistance (oil swelling = 12%) in comparison to commercial TPVs with similar hardnesses. The experimental results indicate that high-performance TPNRs with low hardness values could be prepared with the proper conditions developed in this study. © 2012 Wiley Periodicals, Inc. J. Appl. Polym. Sci., 2013

Carbon black-filled natural rubber composites were prepared using various types of natural rubber: unmodified natural rubber, epoxidized natural rubber with two levels of epoxy groups at 25 and 50 mol % [epoxidized natural rubber (ENR)-25 and ENR-50], and maleated natural rubber. Two types of carbon black (HAF and ECF) with different structure and surface area were used. The functional groups present in natural rubber and carbon black were characterized by FTIR and 1 H-NMR. Furthermore, cure characteristics, mechanical, morphological, and electrical properties of composites and gum rubber compounds were investigated. It was found that the presence of polar functional groups in rubber molecules and the different structures of carbon black significantly affected the cure characteristics and mechanical properties. This is attributed to physical and chemical interactions between carbon black surfaces and rubber molecules. It was also found that natural rubber filled with ECF showed the highest Young’s modulus and hardness, which is due to the high-surface area and structure of the ECF causing an increase in the degree of entanglement between rubber chains and carbon black particles. Frequency dependency of the dielectric constant, loss tangent, and AC conductivity was also investigated. An increase in dielectric constant, loss tangent, and AC conductivity was observed in the ENR/ECF composites. High-carbon black loading level caused network formation of these conductive particles, increasing the AC conductivity of the composites. POLYM. COMPOS.

A simple blend (i.e., blend without curative) of 60/40 rubber/nylon-12 with three different types of natural rubber (i.e., air-dried sheet natural rubber (ADS) and epoxidized natural rubbers (ENR) with 25 and 50 mol% epoxide) was prepared by the melt-mixing process. Influence of different types of rubbers and the level of epoxide groups in ENR molecules on the properties of the blends were investigated. It was found that all the blends exhibited a co-continuous phase morphology. Furthermore, the ENR/nylon-12 blends exhibited superior mechanical properties, stress relaxation behavior, thermal and rheological properties, and a finer grain morphology than that of the ADS/nylon-12 blend. This may be attributed to the higher interfacial adhesion between the ENR and nylon-12 phases via a chemical interaction of epoxide groups in ENR molecules and polar functional groups in the nylon-12 molecules. Temperature scanning stress relaxation (TSSR) measurement was also performed. Improvement in stress relaxation and thermal resistance of the blends with ENR was observed. Moreover, the higher temperature coefficient and lower glass transition temperature (Tg) of the nylon-12 phase in the ENR-50/nylon-12 blends were found. © 2011 Wiley Periodicals, Inc. Adv Polym Techn 32: 118–129, 2012; View this article online at wileyonlinelibrary.com. DOI 10.1002/adv.20243

Epoxidized natural rubber (ENR) and thermoplastic polyurethane (TPU) blends were prepared by simple blend and dynamic vulcanization. The main objective was to prepare a low-hardness TPU material with good damping and elastic and mechanical properties. It was found that the incorporation of ENR into the blend shows a reduction in Young's modulus, hardness (i.e.

Thermoplastic natural rubber based on polyamide-12 (PA-12) blend was prepared by melt blending technique. Influence of blending techniques (i.e., simple blend and dynamic vulcanization) and types of natural rubber (i.e., unmodified natural rubber (NR) and epoxidized natural rubber (ENR)) on properties of the blends were investigated. It was found that the simple blends with the proportion of rubber ∼ 60 wt % exhibited cocontinuous phase structure while the dynamically cured blends showed dispersed morphology. Furthermore, the blend of ENR exhibited superior mechanical properties, stress relaxation behavior, and fine grain morphology than those of the blend of the unmodified NR. This is attributed to chemical interaction between oxirane groups in ENR molecules and polar functional groups in PA-12 molecules which caused higher interfacial adhesion. It was also found that the dynamic vulcanization caused enhancement of strength and hardness properties. Temperature scanning stress relaxation measurement revealed improvement of stress relaxation properties and thermal resistance of the dynamically cured ENR/PA-12 blend. This is attributed to synergistic effects of dynamic vulcanization of ENR and chemical reaction of the ENR and PA-12 molecules. Furthermore, the dynamically cured ENR/PA-12 blend exhibited smaller rubber particles dispersed in the PA-12 matrix. © 2011 Wiley Periodicals, Inc. J Appl Polym Sci, 2011

Thermal and mechanical degradation of natural rubber (NR) mixed with N-(1,3-dimethylbutyl)-N′-phenyl-p-phenylenediamine (6PPD), polymerized 1,2-dihydro-2,2,4-trimethyl-quinoline (TMQ), and 50/50 weight basis mixture under high temperature and shearing conditions were investigated using a moving die processability test and FTIR spectroscopy. Relationship between dynamic properties in terms of tan δ value and chemical changes of NR molecules during degradation were correlated. The results indicated that the NR mixed with antioxidants caused decreased level of chain scission and oxidative degradation. The 6PPD provided better protection of NR against degradation at elevated temperature than TMQ. Furthermore, it was found that a prolonged mixing time caused more pronounced oxidative degradation on NR molecules than increased mixing temperature. The antioxidative capability of those antioxidants on NR was ordered based on their effectiveness as follows: 6PPD > 6PPD mixed with TMQ > TMQ. It was also found that the moving die processability test and FTIR spectroscopy are efficient routes to estimate the oxidative degradation of NR molecules. Therefore, the techniques could be applied to assess or compare antioxidative capability of various types and amounts of antioxidants used in the rubber formulation within a reasonable testing time. © 2009 Wiley Periodicals, Inc. J Appl Polym Sci, 2010

Mechanical, dynamic, thermal, and morphological properties of dynamically cured 60/40 NR/PP TPVs with various loading levels of paraffinic oil were investigated. It was found that stiffness, hardness, tensile strength, storage shear modulus, complex viscosity, glass transition temperature (Tg) of the vulcanized rubber phase, degree of crystallinity and crystalline melting temperature (Tm) of the polypropylene (PP) phase decreased with increasing loading levels of oil. This is attributed to distribution of oil into the PP and vulcanized rubber domains causing oil-swollen amorphous phase and vulcanized rubber domains. An increasing trend of elastic response in terms of tension set and damping factor was observed in the TPVs with loading levels of oil in a range of 0–20 phr. It is supposed that a major proportion of oil was first preferably migrated into the PP phase and caused an abrupt decreasing trend of degree of crystallinity and Tm of the PP phase. The dispersed vulcanized rubber domains remained small as particles with a low degree of swelling. Increasing loading levels of oil higher than 20 phr caused a decreasing trend of elongation at break and elastomeric properties. Saturation of oil in the PP phase was expected and the excess oil was transferred to the rubber phase which thereafter caused larger swollen vulcanized rubber domains. The remaining amount of oil was able to separate as submicron pools distributed in the PP matrix. This caused lowering of Tg, Tm, crystallinity of PP phase as well as strength, elastomeric, and dynamic properties of the TPVs. © 2009 Wiley Periodicals, Inc. J Appl Polym Sci, 2010

Graft copolymers of natural rubber and poly (methyl methacrylate) (NR-g-PMMA) were prepared in a laboratory scale, and then extended to a pilot scale production. Reaction conditions were first assessed based on a preparation in the laboratory scale with a reactor capacity of 1.5 l. An optimum grafting efficiency was obtained when cumene hydroperoxide/tetraethylenepentamine (CHP/TEPA) redox initiator was used at the reaction temperature and time of 50°C and 3 h, respectively. MMA monomer was used without purification in the polymerization process comparing with the purified one by means of extraction. It was found that only a slight decrease of grafting efficiency was observed when the nonpurified monomer was used in the reaction. The nonpurified monomer was therefore used to prepare the NR-g-PMMA in a pilot scale production with a reactor capacity of 260 L. Various weight ratios of NR/MMA at 50/50, 60/40, 70/30, and 85/15 were studied. The resulting graft copolymers were characterized by FTIR and 1H-NMR techniques. It was found that increasing concentration of MMA caused an increase of free PMMA (i.e., homopolymer) but a decrease of free NR (i.e., ungrafted NR) and grafting efficiency. Quantity of grafted PMMA on the NR backbone was estimated using the integrated peak areas of 1H-NMR spectra and quantitative analysis by extraction method. The results were found to be in good agreement. © 2009 Wiley Periodicals, Inc. J Appl Polym Sci, 2009

Dynamically cured 60/40 NR/HDPE blends with various amounts of phenolic curative were prepared in an internal mixer at 160°C. A simple blend (i.e., the blend without curative) was also prepared using the same materials and blend proportion for comparison purposes. Mechanical, dynamic, and morphological properties; swelling resistance and crosslink density of the blends were investigated. It was found that the thermoplastic vulcanizates (TPVs) gave superior mechanical and dynamic properties than the simple blend. Furthermore, the mechanical properties in terms of elongation at break, modulus and tensile strength and elastic response in dynamic test in terms of storage modulus increased with increased loading amount of the curative. The complex viscosity also increased but the tan δ and tension set decreased with increased loading level of the curative. The crosslink density of the TPVs was estimated based on the elastic shear modulus. It was found that the crosslink density of the blends increased with increased loading levels of the curative while the degree of swelling decreased. This correlated well with the trend of mechanical and dynamic properties. SEM micrographs were used to confirm the level of mechanical and dynamic properties. It was found that the simple blend at a given blend ratio exhibited co-continuous phase morphology. However, the TPVs showed micron scale of vulcanized rubber domains dispersed in a continuous HDPE matrix. The size of vulcanized rubber domains decreased with increasing amounts of the curative. This led to greater interfacial adhesion between the phase and hence superior mechanical and dynamic properties. © 2009 Wiley Periodicals, Inc. J Appl Polym Sci, 2009

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

Maleated natural rubbers (MNRs) were prepared using various levels of maleic anhydride (MA) at 4, 6, 8, 10, and 12 phr. Dynamically cured 60/40 MNR/PP blends with phenolic-modified polypropylene (Ph-PP) compatibilizer at a loading level of 5 wt % of PP were prepared by melt mixing process using sulfur vulcanization system. The influence of the level of MA on properties of the thermoplastic vulcanizates (TPVs) was studied. It was found that the mixing torque, apparent shear stress, shear viscosity, tensile strength, and hardness properties increased with increasing levels of the MA or grafted succinic anhydride groups in the MNR molecules. This is attributed to an increase in chemical interaction and reaction between methylol groups in the Ph-PP molecules and polar functional groups in the MNR molecules upon increasing levels of the grafted succinic anhydride groups. As a consequence, compatibilizing block copolymers of MNR and PP blocks were formed. The block copolymers were capable of compatibilizing with MNR and PP blend components via the respective blocks. Recyclability of the MNR/PP TPVs was also studied. It was found that, after processing through a number of cycles by injection molding and extrusion processing, the TPV exhibited marginal decreases in mechanical properties. This corresponded to slightly increasing size of the dispersed vulcanized rubber domains. © 2008 Wiley Periodicals, Inc. J Appl Polym Sci, 2008

Thermoplastic elastomers (TPEs) based on dynamically cured epoxidized natural rubber/high-density polyethylene (ENR/HDPE) blends were prepared. Influence of the process oil, blend proportion, and curing systems were investigated. It was found that the oil-extended thermoplastic vulcanizates (TPVs) exhibited better elastomeric properties and improved ease of the injection process. Increasing the proportion of ENR caused increasing elastic response of elongation at break, tension set properties, and tan δ. It was also found that the TPV treated with phenolic resin exhibited superior mechanical properties and the smallest vulcanized rubber domains. The TPV treated with the conventional peroxide co-agent curing system showed superior strength properties but had poor elastomeric properties. POLYM. ENG. SCI., 2009. © 2008 Society of Plastics Engineers

Epoxidized natural rubber (ENR) with a level of epoxide groups of 20 mol % was prepared via the performic epoxidation method. It was then used to blend with high-density polyethylene (HDPE) at various blend ratios. Three types of blend compatibilizers were prepared. These included a graft copolymer of HDPE and maleic anhydride (MA; i.e., HDPE-g-MA) and two types of phenolic modified HDPEs using phenolic resins SP-1045 and HRJ-10518 (i.e., PhSP-PE and PhHRJ-PE), respectively. We found that the blend with compatibilizer exhibited superior tensile strength, hardness, and set properties to that of the blend without compatibilizer. The ENR and HDPE interaction via the link of compatibilizer molecules was the polar functional groups of the compatibilizer with the oxirane groups in the ENR molecules. Also, another end of the compatibilizer molecules (i.e., HDPE segments) was compatibilizing with the HDPE molecules in the blend components. The blend with compatibilizer also showed smaller phase morphology than the blend without compatibilizer. Among the three types of the blend compatibilizer, HDPE-g-MA provided the blend with the greatest strength and hardness properties but the lowest set properties. © 2008 Wiley Periodicals, Inc. J Appl Polym Sci, 2008

Thermoplastic elastomer (TPE) comprising air-dried sheet or natural rubber (ADS or NR) and high-density polyethylene (HDPE) was prepared by a simple blending technique. NR and HDPE were mixed with each type of phenolic compatibilizer (HRJ-10518 or SP-1045) or liquid natural rubber (LNR) at 180°C in an internal mixer. The mixing torque, shear stress, and shear viscosity of the blends increased with increasing amounts of NR. Positive deviation blend (PDB) for the blends containing active hydroxyl methyl phenolic resin in HRJ-10518 or dimethyl phenolic resin in SP-1045 was obtained. PDB was not observed for the blends without the compatibilizers or with LNR. The blends with HRJ-10518 or SP-1045 were compatible or partially compatible while the LNR blends were incompatible. In the phenolic compatibilized blends, NR dispersed in the HDPE matrix was found in the NR/HDPE blends of 20/80, 40/60, and 50/50 ratios. HDPE dispersed in NR matrix was obtained in the NR/HDPE blend of 80/20 ratio, and the co-continuous phase was accomplished in the NR/HDPE blend of 60/40 ratio. The NR/HDPE blend at 60/40 ratio compatibilized with HRJ-10518 and fabricated by a simple plastic injection molding machine exhibited higher ultimate tensile strength and elongation at break (EB). Incorporation of parafinic oil caused a decreasing tendency in tensile strength with increases in EB. The TPNRs exhibited high elastomeric nature with low-tension set. Copyright © 2007 John Wiley & Sons, Ltd.

Thermoplastic vulcanizates (TPVs) from natural rubber (NR) and polypropylene (PP) were studied, prepared by dynamic vulcanization during melt mixing, using various peroxides to crosslink the rubber phase. The objective was to find a proper balance between degree of crosslinking of the rubber and degradation of the PP-phase, and the tendency of the peroxide to form smelly by-products, in particular acetophenone. Four types of peroxides were investigated: 2,5-dimethyl-2,5-di(tert-butyl-peroxy) hexyne-3 (DTBPHY), 2,5-dimethyl-2,5-di(tert-butyl-peroxy) hexane (DTBPH), di(tert-butylperoxyisopropyl) benzene (DTBPIB), and dicumyl peroxide (DCP), at two mixing temperatures: 160 and 180°C for a 60/40 NR/PP TPV. The maximum and final mixing torques are clearly related to the intrinsic decomposition temperature of the particular peroxide used, where DCP and DTBPIB turn out to be effective at 160°C, whereas the other two require a higher temperature of 180°C. The best mechanical properties, tensile strength, elongation at break and compression set are obtained at lower mixing temperature with DCP and DTBPIB, presumably due to less degradation of the NR and PP. Unfortunately, these two peroxides form more smelly by-products than DTBPHY and DTBPH. Dependent on the requirements of the pertinent application, a balanced selection needs to be made between the various factors involved to obtain an optimal product performance of these NR/PP TPVs.

Para rubber wood particleboard (PB) was prepared using NR based adhesives and hot pressing processes. Two types of NR based adhesives were used; epoxidized natural rubber (ENR) and unmodified NR. The ENR latex was prepared using in situ performic epoxidation. Molecular weight of the ENR molecules was then reduced by incorporating of a reducing agent; sodium nitrite solution. A chain scission reaction and epoxidation simultaneous occurred via a chain-scission parallel epoxidation mechanism. Sulphur and multifunctional amine (i.e., hexamethoxymethylmelamine) curing systems were used to cure the adhesives. It was found that the hexamethoxymethylmelamine gave the PB with higher tensile strength than that of the sulphur vulcanization system. Furthermore, the tensile strength increased with increasing concentration of citric acid in the compounding formulation. Adhesion of the ENR adhesive with Parawood sawdust was observed to imporve by reducing molecular weight of the ENR molecules. That is, the highest tensile strength of the PB was observed for the ENR adhesive with the lowest (i.e., 1.10 × 105). This may be attributed to the adhesive with lower molecular weight exhibited greater ability to wet or cover the wood particle surfaces. As a consequence, greater chemical interaction between the adhesive and the wood particles was observed. POLYM. ENG. SCI., 47:421–428, 2007. © 2007 Society of Plastics Engineers.

In polymeric materials combining desirable properties, compatibility between constituent components of incompatible blends is necessary. The influence of two types of blend compatibilizers, a graft copolymer of maleic anhydride and polypropylene (PP) and phenolic-modified PP, on the rheological, mechanical, and morphological properties of epoxidized natural rubber/PP thermoplastic vulcanizates was investigated at varied concentrations. All properties improved in a range of loading levels of compatibilizers at 0–7.5 wt % of PP. This was attributed to a chemical interaction between the different phases caused by the functionalized compatibilizers. Increasing chemical interaction between interfaces improved the interfacial tension and led to a microscale size of the dispersion. A decreasing trend in the properties was observed at compatibilizer levels higher than 7.5 wt % of PP because of segregation, which led to a third blend component dispersed in the PP matrix. The compatibilizers behaved as lubricants in the polymer melt flow. © 2007 Wiley Periodicals, Inc. J Appl Polym Sci, 2008

The vulcanization of natural rubber (NR)-blended acrylonitrile–butadiene–styrene (ABS) was carried out with a phenolic curing agent by a melt-mixing process. The NR compound was first prepared before blending with ABS. The effects of the phenolic curative contents (10, 15, and 20 phr) and blend proportions (NR/ABS ratio = 50 : 50, 60 : 40, and 70 : 30) on the mechanical, dynamic, thermal, and morphological properties of the vulcanized NR/ABS blends were investigated. The tensile strength and hardness of the blends increased with increasing ABS content, whereas the elongation at break decreased. The strength property resulting from the thermoplastic component and the vulcanized NR was an essential component for improving the elasticity of the blends. These blends showed a greater elastic response than the neat ABS. The thermal stability of the blends increased with increasing ABS component. Scanning electron micrographs of the blends showed a two-phase morphology system. The vulcanized 60 : 40 NR/ABS blend with 15-phr phenolic resin showed a uniform styrene-co-acrylonitrile phase dispersed in the vulcanized NR phase; it provided better dispersion between the NR and ABS phases, and this resulted in superior elastic properties. © 2015 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2015, 132, 42520.

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.

Epoxidized natural rubbers (ENR) with various levels of epoxide groups were prepared. Thermoplastic vulcanizates based on 75/25 ENRs/PP blends with Ph-PP compatibilizer were later prepared by dynamic vulcanization using sulfur curing system. Influence of various levels of epoxide groups on rheological, mechanical morphological properties, and swelling resistance of the TPVs was investigated. It was found that the mixing torque, apparent shear stress, apparent shear viscosity, tensile strength, and hardness properties increased with increasing levels of epoxide groups in the ENR molecules. This may be attributed to increasing level of chemical interaction between the methylol groups of the Ph-PP molecules and polar functional groups of the ENR molecules. Also, the PP segments in the Ph-PP molecules are capable of compatibilizing with the PP molecules used as a blend composition. In SEM micrographs, we observed finer dispersion of vulcanized rubber domains as increasing levels of epoxide contents. This corresponds to increasing trend of strength and hardness properties of the TPVs. An increasing trend of tension set and a decreasing trend of elongation at break were observed as increasing levels of epoxide groups in the ENR molecules. This is because of higher rigidity of the vulcanized ENR phase with higher epoxide groups. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 101: 3046–3052, 2006

Epoxidized natural rubber (ENR) was prepared using the performic epoxidation method. TPVs based on ENR/PP blends were later prepared by melt-mixing processes via dynamic vulcanization. The effects of blend ratios of ENR/PP, types of compatibilizers, and reactive blending were investigated. Phenolic modified polypropylene (Ph-PP) and graft copolymer of maleic anhydride on polypropylene molecules (PP-g-MA) were prepared and used as blend compatibilizers and reactive blending components of ENR/Ph-PP and ENR/PP-g-MA blends. It was found that the mixing torque, apparent shear stress and apparent shear viscosity increased with increasing levels of ENR. This is attributed to the higher viscosity of the pure ENR than that of the pure PP. Furthermore, there was a higher compatibilizing effect because of the chemical interaction between the polar groups in ENR and PP-g-MA or Ph-PP. Mixing torque, shear flow properties (i.e., shear stress and shear viscosity) and mechanical properties (i.e., tensile strength, elongation at break, and hardness) of the TPVs prepared by reactive blending of ENR/Ph-PP and ENR/PP-g-MA were lower than that of the samples without a compatibilizer. However, the TPVs prepared using Ph-PP and PP-g-MA as compatibilizers exhibited higher values. We observed that the TPVs prepared from ENR/PP with Ph-PP as a compatibilizer gave the highest rheological and mechanical properties, while the reactive blending of ENR/PP exhibited the lowest values. Trend of the properties corresponds to the morphology of the TPVs. That is, the TPV with Ph-PP as a blend compatibilizer showed the smallest rubber particles dispersed in the PP matrix, while the reactive blending of ENR/PP-g-MA showed the largest particles. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 100: 4729–4740, 2006