Graft‐modified HCPE with methyl methacrylate by the mechanochemistry reaction. II. Physical‐mechanical properties and processability

In this article, the physical‐mechanical properties and processability of graft‐modified highly chlorinated polyethylene (HCPE; chlorine contents: ≥ 60%) with methyl methacrylate (MMA) by mechanochemistry reaction were studied. The results showed that the HCPE‐g‐MMA system is superior to unmodified HCPE in physical‐mechanical properties, particularly in processability. In addition, the HCPE‐g‐MMA system, with about 62% chlorine content, was the same as PVC in its physical‐mechanical properties. The HCPE‐g‐MMA system, with about 65.5% chlorine content, is the same as chlorinated poly(vinyl chloride) (CPVC) in its physical‐mechanical properties, except that the Vicat softening temperature and processability of HCPE‐g‐MMA system are superior to PVC and CPVC. Compared with PVC and CPVC, the HCPE‐g‐MMA system proves better due to its lack of a toxic monomer. © 2003 Wiley Periodicals, Inc. J Appl Polym Sci 91: 282–287, 2004     

Natural rubber‐g‐methyl methacrylate/poly(methyl methacrylate) blends

The grafting of the methyl methacrylate (MMA) monomer onto natural rubber using potassium persulfate as an initiator was carried out by emulsion polymerization. The rubber macroradicals reacted with MMA to form graft copolymers. The morphology of grafted natural rubber (GNR) was determined by transmission electron microscopy and it was confirmed that the graft copolymerization was a surface‐controlled process. The effects of the initiator concentration, reaction temperature, monomer concentration, and reaction time on the monomer conversion and grafting efficiency were investigated. The grafting efficiency of the GNR was determined by a solvent‐extraction technique. The natural rubber‐g‐methyl methacrylate/poly(methyl methacrylate) (NR‐g‐MMA/PMMA) blends were prepared by a melt‐mixing system. The mechanical properties and the fracture behavior of GNR/PMMA blends were evaluated as a function of the graft copolymer composition and the blend ratio. The tensile strength, tear strength, and hardness increased with an increase in PMMA content. The tensile fracture surface examined by scanning electron microscopy disclosed that the graft copolymer acted as an interfacial agent and gave a good adhesion between the two phases of the compatibilized blend. © 2001 John Wiley & Sons, Inc. J Appl Polym Sci 81: 428–439, 2001     

氯化石蜡共混改性天然胶乳的研究

分别采用氯化石蜡、氯化石蜡／Sb2O3共混改性天然胶乳．考察了改性胶乳硫化胶膜的力学性能及阻燃性能．并进行了TG·DTG和DSC分析。结果表明：改性胶乳的阻燃效果比未改性天然胶乳的高．且氯化石蜡／Sb2O3共混改性天然胶乳可产生协同阻燃效果；随Sb2O3用量的增加．硫化胶膜撕裂强度增加．而拉伸强度下降。氯化石蜡／Sb2O3改性胶乳的热降解过程为二步反应．且起始热降解温度比天然胶乳的低．玻璃化转变温度提高。     

不同品系天然橡胶胶乳的性能研究

对同一割龄6个品系的鲜胶乳,将其浓缩后比较各品系浓缩胶乳的性能,浓缩胶乳硫化胶膜的物理机械性能进行研究.结果表明热研8-79鲜胶及浓乳的干胶和总固含量最高,热研88-13的钙镁含量最高,RRIM600的分子量最大,硫化胶膜物理机械性能最好.     

“胶乳共混法”制备天然橡胶／二氧化硅纳米复合材料及其性能

采用γ-甲基丙烯酰氧基丙基三甲氧基硅烷（KH570）改性纳米二氧化硅（SiO2）,然后通过乳液聚合接枝上聚甲基丙烯酸甲酯（PMMA）,再将其与甲基丙烯酸甲酯（MMA）改性的天然胶乳,通过胶乳共混法制备天然橡胶／二氧化硅纳米复合材料,结果显示,纳米二氧化硅表面接枝上了PMMA,二氧化硅在橡胶基体中分散良好,粒径在60～100nm之间,得到的胶膜力学性能有很大的提高。     

Novel thermoplastic natural rubber based on thermoplastic polyurethane blends: influence of modified natural rubbers on properties of the blends

Three different forms of natural rubber: maleated natural rubber (MNR), epoxidized natural rubber (ENR) and natural rubber-graft-poly(methyl methacrylate) (NR-g-PMMA) were prepared. Degree of functional groups in rubber molecules was quantified using the integrated peak areas of ¹H NMR. It was found that the modified rubbers with similar level of functionality had been successfully prepared. Thermoplastic natural rubber (TPNR) based on blending of thermoplastic polyurethane (TPU) and various forms of rubber were then prepared using melt blending method. The properties of the blends were studied and compared together in relation to different types of natural rubbers prepared (i.e., unmodified NR, MNR, ENR and NR-g-PMMA). It was found that the blends with modified NR exhibited superior stiffness, entropy effect and damping factor compared to other blends with unmodified NR. This is attributed to the chemical interaction between the functional groups of modified NR molecules and polar functional groups in TPU molecules which facilitated higher interfacial adhesion between both phases. The chemical interaction was verified by ATR-FTIR and TSSR techniques. It was also found that the MNR/TPU blend showed the highest tensile modulus, mechanical and elastic properties with smallest and finer grain dispersion of co-continuous phase compared to ENR/TPU, NR-g-PMMA/TPU and unmodified NR/TPU blends, respectively. This might be due to higher chemical interactions between MNR and TPU phases. Furthermore, the incorporation of rubber did reduce hardness (i.e., <60 Shore A) with improvement of elasticity of the blends compared with the original TPU (i.e., ~85 Shore A).     

马来酸酐和苯乙烯接枝改性对天然橡胶/聚丙烯共混物物理机械性能的影响

用动态硫化法制备了天然橡胶(NR)/聚丙烯(PP)热塑性弹性体(TPV)。研究了马来酸酐/苯乙烯/过氧化二异丙苯(MAH/St/DCP)多单体熔融接枝交联改性及纳米二氧化硅用量对NR/PP TPV物理机械性能的影响,讨论了NR/PP TPV的重复加工性能。结果表明,当MAH/St/DCP用量为3.750/1.875/0.375质量份、纳米二氧化硅用量为3质量份时,NR/PP TPV的物理机械性能最好,达到了国内外有关通用橡胶/PP TPV的水平,并且具有较好的重复加工性能。     

Green Composites from Natural Rubber and Oil Palm Fiber: Physical and Mechanical Properties

Natural rubber (NR) composites were prepared by incorporating short oil palm fibers of different lengths (viz., 2, 6, 10, and 14 mm) into natural rubber matrix in a mixing mill according to a base formulation. The curing characteristics of the mixes were studied and the samples were vulcanized at 150°C. The vulcanization parameters, processability characteristics, and tensile properties of these composites were analyzed. The effects of fiber length, orientation, loading, and fiber-matrix interaction on the mechanical properties of the green composites were studied. The reinforcement property of the alkali-treated fiber was compared with that of the untreated one. The extent of fiber orientation was studied from green strength measurements. From anisotropic swelling studies, the extent of fiber alignment and the strength of fiber–rubber interface adhesion were analyzed. Scanning electron microscopic (SEM) studies were carried out to analyze the fiber surface morphology, fiber pullout, and fiber–rubber interface.     

Phosphorus modification of epoxidized liquid natural rubber to improve flame resistance of vulcanized rubbers

The use of phosphorus for improving flame retardancy of natural rubber vulcanizates was attempted by incorporating a modified form of natural rubber. By reacting epoxidized liquid natural rubber (ELNR) with dibutylphosphate it was possible to chemically modify the polymer. On a 25% epoxidized LNR, 5.2–6.8% w/w of phosphorus could be fixed on the polymer backbone. The reaction carried out in bulk and solution resulted in products with different T_g values probably due to the varying crosslink levels in the resultant products. Chemical analysis of the modified polymers prepared by two sets of reactions under identical conditions proved the reproducibility of the reactions in bulk and in solution. Incorporation of the phosphorus-modified ELNR in a natural rubber formulation decreased the flammability behaviors of the vulcanizate. On the other hand, a decrease of the rate of curing and mechanical properties was observed. The phosphorus addition could also be carried out by mixing ELNR and dibutylphosphate at the time of mixing the compounds and resulted in equally good flame retardance with relatively better processing and mechanical properties. © 1994 John Wiley & Sons, Inc.     

Zn(MMA)_2对硫黄硫化天然橡胶性能的影响

甲基丙烯酸锌(Zn(MMA)_2)在自由基存在下可以与橡胶发生接枝和交联反应,在橡胶中引入金属离子键交联结构,发生自聚合反应生成纳米聚盐粒子等,使得硫化橡胶具有多元的交联网络结构和多元的填充网络结构,这使得硫化胶的物理力学性能大大提高。为了获得Zn(MMA)_2所给出的优异性能,需采用过氧化物硫化体系,虽然过氧化物与硫黄并用的体系有很多报道,但是都没有单纯采用过氧化物硫化时的性能好。由于硫黄硫化是不饱和橡胶最广泛采用的硫化体系,因此在硫黄硫化条件下,获得Zn(MMA)_2的优异性能,无疑是非常有意义的。从化学计量角度设计了胶料中硫黄的摩尔用量远远大于Zn(MMA)_2的摩尔用量(14:1/mol:mol)的情况,对比了三种硫化体系(S、Zn(MMA)_2/S、Zn(MMA)_2/S*)硫化天然橡胶的特点。结果表明Zn(MMA)_2/S体系硫化胶料的物理力学性能显著提高,这使在硫黄硫化体系中实现Zn(MMA)_2的优异性能成为可能。论文分析阐述了产生这些结果的原因并提出了可能的机理     

The effect of devulcanization level on mechanical properties of reclaimed rubber by thermal‐mechanical shearing devulcanization

Ground tire rubber (GTR) with crosslinked structure has hardly any plasticity and processability, which makes its property very poor. Thermal‐mechanical shearing devulcanization method can effectively destroy the crosslinked structure and restore GTR a certain extent of plasticity and processability. This article investigated the characteristic and reprocessing performance of reclaimed rubber prepared through thermal‐mechanical shearing devulcanization. The relationship between the devulcanization level (indicated by gel fraction and crosslink density) and the mechanical property was analyzed by sufficient experiments. Fourier transform infrared spectroscopy and elemental analyzer studies revealed the chemical structure of GTR changed and many complex reactions occurred after devulcanization. The gel permeation chromatography indicated the specific changes of molecular weight and molecular weight distribution in devulcanization process. The differential scanning calorimetry revealed various vulcanized abilities and vulcanized structures of reclaimed rubber. The scanning electron microscope further confirmed the recovery of plasticity after devulcanization and the distinct vulcanized structures between revulcanizates. The determination of devulcanization level and mechanical properties verified that mechanical properties especially tensile strength reached to the optimum value only at an appropriate devulcanization level. © 2013 Wiley Periodicals, Inc. J. Appl. Polym. Sci., 2013     

Natural rubber–isotactic polypropylene thermoplastic blends

Thermoplastic elastomers, prepared by melt blending of natural rubber (NR) and isotactic polypropylene (PP) through a dynamic vulcanization technique, were developed during the later 1970s. However, they have certain drawbacks due to thermal degradation and higher molecular weight of NR. In the study reported here, NR was masticated to different levels prior its addition to isotactic polypropylene to improve the flow properties and to reduce the incompatibility resulting from molecular weight mismatch of NR/PP thermoplastic blends. Mixing energy curves of uncrosslinked blends and those of dynamically vulcanized blends crosslinked using different cure systems were compared. The mixing energy curves of blends containing NR of different molecular weight (M _n) and two grades of PP (injection and film grades) were also compared. Technological and processing properties of the dynamically vulcanized (sulphur and peroxide cure systems) and unvulcanized blends were compared with those of the samples containing unmasticated NR. The results indicated that a number average molecular weight in the range 4 × 10⁵ for NR increased the procoessability without significantly affecting the technological properties of NR/PP thermoplastic blends. Among the three cure systems studied Luperox 101 and dicumyl peroxide gave better technological properties than the sulphur‐cured samples. Two antioxidants, viz. quinoline (TDQ) and imidazole (MBI) type, were tried in NR/PP blends. It was found that TDQ imparts better aging resistance compared to MBI. The improvement in processability due to the reduction in molecular weight of natural rubber by mastication is more noticeable in the case of peroxide vulcanized blends compared to sulphur vulcanized samples. © 2004 Wiley Periodicals, Inc. J Appl Polym Sci 92: 2063–2068, 2004     

Preparation of natural rubber-montmorillonite nanocomposite in aqueous medium: evidence for polymer-platelet adhesion

Nanocomposites of natural rubber latex and layered silicates are prepared by a mild dispersion shear blending process. The results of X-ray diffraction (XRD) and transmission electron microscopy (TEM) show that clay particles are well dispersed in the dry latex and the platelets have a preferential orientation, forming translucent nanocomposites. These show tensile mechanical properties analogous to those obtained with vulcanized rubber as well as an increased solvent resistance, which is expected considering that there is significant adhesion between clay lamellae and rubber. Nanocomposite swelling is strongly anisotropic. Natural rubber properties may thus be strongly modified by nanocomposite formation producing unprecedented combinations of properties.     

蛋白质对天然橡胶及其性能影响的研究

天然橡胶(NR)的主要成分为橡胶烃、水、非胶物质,其中非胶物质中蛋白质的含量对其性能的影响最大.本文分析了天然胶乳中的蛋白质的结构,介绍了低蛋白天然胶乳的制备及其性能的研究概况、蛋白质对其硫化及力学性能影响研究现状,并对低蛋白天然胶市场前景进行了分析与展望.     

Synthesis,characterization, and enzymatic degradation of starch-grafted poly(methyl methacrylate) copolymer films

Graft copolymerization of methyl methacrylate (MMA) onto the corn starch (CS) backbone was carried out in an aqueous medium using ceric ammonium nitrate as an initiator under nitrogen atmosphere. The weight ratio of CS/MMA varied with their composition, as 7/3, 6/4, 5/5, 4/6, and 3/7 were used in this study of the graft efficiency and graft percentage (GP); thus, five different GP CS-g-PMMA copolymers were obtained. The molecular weight of CS-g-PMMA copolymers were measured by using gel permeation chromatography. The structure of CS and CS-g-PMMA copolymer were confirmed by infrared spectra. CS and CS-g-PMMA copolymers were characterized by thermal gravimetric analysis, differential scanning calorimetry, and scanning electron microscopy (SEM). Horowitz-Metzger and Broido methods were applied to investigate the thermal decomposition kinetics of CS-g-PMMA copolymers. The effect of GP on the activation energy of decomposition, crystallization behavior, and morphology was investigated. In addition, the biodegradability of CS-g-PMMA films were also studied by α-amylase treatment with different times. The weight loss of CS-g-PMMA films after α-amylase treatment were calculated. Finally, the morphology of CS-g-PMMA films before and after α-amylase treatment were observed by SEM photograph. © 2011 Wiley Periodicals, Inc. J Appl Polym Sci, 2012     

Reinforcement effect of poly (methyl methacrylate)-<Emphasis Type="Italic">g</Emphasis>-cellulose nanofibers on LDPE/thermoplastic starch composites: preparation and characterization

The effect of cellulose nanofibers (CNFs) and poly [methyl methacrylate (MMA)]-grafted cellulose nanofibers (CNF-g-PMMA) on mechanical properties and degradability of a 75/25 low density polyethylene/thermoplastic starch (LDPE/TPS) blend was investigated. Graft copolymerization on CNFs was performed in an aqueous suspension by free radical polymerization using MMA as an acrylic monomer. In addition, a LDPE/TPS blend was reinforced by different amounts of CNFs (1–5 wt%) and CNF-g-PMMA (1–7 wt%) using a twin-screw extruder. A 61% grafting of PMMA on the surface of CNFs was demonstrated by gravimetric analysis. Moreover, after modification the X-ray photoelectron spectroscopy analysis showed a 20% increase of carbon atoms on the surface of CNFs and a 22.6% decrease in the oxygen content of its surface. The mechanical properties of the CNFs-modified composites were significantly improved compared to the unmodified nanocomposites. The highest tensile strength and Young’s modulus were obtained for the composites reinforced by 3 and 7 wt% CNF-g-PMMA, respectively. The degradability of cellulose nanocomposites was studied by water absorption and soil burial tests. Surface modification of CNFs lowered water absorption, and soil burial test of the LDPE/TPS blend showed improvement in biodegradability by addition of CNF-g-PMMA.     

纳米蒙脱土改性天然胶乳的制备及其性能研究

采用胶乳接枝插层法制备了纳米蒙脱土改性天然胶乳，并对其性能进行了研究。结果表明，采用胶乳接枝插层法不仅能实现天然胶乳与甲基丙烯酸甲酯（MMA）的接枝，而且能与有机改性蒙脱土插层。通过这种方法制备的改性胶乳的硫化胶乳胶膜具有优良的物理性能和热力学性能。     

Contribution of hydrogen and/or covalent bonds on reinforcement of natural rubber latex films with surface modified silica

A macromolecular coupling agent containing hydrophilic and hydrophobic groups is made to react with precipitated silica. Interfacial interactions between  OH groups of silica and  COOH groups of macromolecule are found to be created through either hydrogen bonds alone or through hydrogen bonds and covalent bonds. Aqueous dispersions of unmodified and modified silica are prepared and the colloidal stability and particle size distribution of the dispersions are observed. The dispersions at neutral pH are incorporated into vulcanized/unvulcanized natural rubber latex. The formation of hydrogen bonds and/or covalent bonds is studied via FTIR spectroscopy and their contribution in encouraging filler‐rubber interactions is emphasized through mechanical and swelling properties. Uniform distribution and dispersion of modified filler particles throughout the rubber matrix is confirmed by the microstructures of the latex films cast from filler added natural rubber latex. © 2014 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2014 , 131, 40380.     

Effect of natural coagula maturation on the processability,cure, and mechanical properties of unfilled vulcanizates of Hevea natural rubber

Fresh latex from different Hevea brasiliensis clones was naturally coagulated, subjected to different durations of maturation, processed into solid rubber, and compounded into pure gum stocks and vulcanized. Coagula maturation had clone‐specific effects on the processability of the raw rubber: reduced for some clones, while others was less sensitive. The cure and mechanical behaviors of the compounded stocks and vulcanizates, respectively, were not sensitive to the clonal origin of coagula and their duration of maturation. Although coagula maturation could be associated with leaching, deactivation of inherent antioxidants in Hevea latex, as well as crosslinking and/or oxidation of polyisoprene chains, these results show that compounding with a standard pure gum recipe compensates for the Hevea latex constituents affected by maturation. Hence, extended maturation of Hevea coagula, for economic or other reasons, would influence much more the bulk behavior of raw rubber and have insignificant effects on the compounded stocks and vulcanizates. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 103: 2359–2363, 2007     

Blends of poly(vinyl chloride) (PVC)/natural rubber‐g‐(styrene‐co‐methyl methacrylate) for improved impact resistance of PVC

To improve the mechanical properties of poly(vinyl chloride) (PVC), the possibility of combining PVC with elastomers was considered. Modification of natural rubber (NR) by graft copolymerization with methyl methacrylate (MMA) and styrene (St) was carried out by emulsion polymerization by using redox initiator to provide an impact modifier for PVC. The impact resistance, dynamic mechanical analysis (DMA), and scanning electron microscopy (SEM) of St and MMA grafted NR [NR‐g‐(St‐co‐MMA)]/PVC (graft copolymer product contents of 5, 10, and 15%) blends were investigated as a function of the amount of graft copolymer product. It was found that the impact strength of blends was increased with an increase of the graft copolymer product content. DMA studies showed that NR‐g‐(St‐co‐MMA) has partial compatibility with PVC. SEM confirmed a shift from brittle failure to ductility with an increase graft copolymer content in the blends. The mechanical properties showed that NR‐g‐(St‐co‐MMA) interacts well with PVC and can also be used as an impact modifier for PVC. © 2004 Wiley Periodicals, Inc. J Appl Polym Sci 93: 1666–1672, 2004