Effects of grafting level and nano-clay loading on the properties of cured NR/PVA blends

Abstract

The primary objective of this study is to improve the properties of NR/PVA blend which is cured using glutaraldehyde at low temperature. PMMA grafted on to NR with different grafting levels has been prepared and confirmed the grafting reaction by TEM, FT-IR and ¹H-NMR. The effect of PMMA contents on NR with 1 phr of nano-clay on the mechanical properties and thermal stability has also been investigated. Significant enhancement in mechanical and thermal stability of the blends with higher grafting level on NR is observed. Activation energy of degradation has been determined from TGA curves by using the Horowitz-Metzger equation. The nature of dispersion and surface morphology has been studied using SEM-EDX technique. The experimental results reveal that the properties can be improved by adding functional group (i.e. PMMA) onto NR molecule.     

纳米二氧化硅与辐射硫化三元乙丙橡胶相互作用的研究

用Kraus方程、IR光谱和交联密度等手段研究了纳米二氧化硅与辐射硫化三元乙丙橡胶间的相互作用。Kraus曲线显示纳米二氧化硅与辐射硫化三元乙丙橡胶之间存在着相互作用；红外光谱的结果表明纳米二氧化硅与橡胶分子发生了化学反应，生成了化学键。用平衡溶胀法测定了纳米二氧化硅填充辐射硫化三元乙丙橡胶的交联密度，发现当填料含量低于40phr时，填充辐射胶的总交联密度随填料用量增加而提高；继续增加填料含量，总交联密度不再继续提高；物理交联密度也呈现出相同的变化趋势。同时，纳米二氧化硅与辐射硫化三元乙丙橡胶的相互作用增强，使得硫化胶的力学性能随着相互作用的加强而得到改善。     

Effect of halloysite nanotube on microstructure,rheological and mechanical properties of dynamically vulcanized PA6/NBR thermoplastic vulcanizates

Dynamically vulcanized thermoplastic vulcanizate (TPV) nanocomposites based on polyamide-6 (PA6) and acrylonitrile butadiene rubber (NBR) reinforced by halloysite nanotubes (HNT) were prepared via a direct melt mixing process. The effects of HNT on the physical, mechanical, and rheological properties of nanocomposites were investigated. The prepared PA6/NBR/HNT nanocomposites were characterized using X-ray diffraction (XRD), scanning electron microscopy (SEM), differential scanning colorimeter (DSC), dynamic mechanical thermal analysis (DMTA), and rheological measurements. The morphology study of prepared nanocomposites shows that the introduction of HNT into the PA6 phase causes a decrease in the size of NBR droplets. The mechanical measurements revealed that Young’s modulus of TPV nanocomposites increased with the HNT loading up to 54%. DMTA results show that the introduction of 10 wt% of HNT into the PA6/NBR TPV leads to a 30% increase in storage modulus. The rheological measurements revealed that the storage modulus of nanocomposites has an increase of more than 200% in the presence of 7 wt% of HNT loading. Analytical stiffness modeling of Young’s modulus of the TPV nanocomposites was investigated using Hui–Shia and Wu models. Both models have some deviations from experimental results and been modified to predict Young’s modulus of the nanocomposites containing HNT with more precisions. The viscosity behavior of TPV nanocomposites was studied using a Carruea–Yasuda model and showed that the yield stress of nanocomposites increases with higher HNT loadings, indicating the formation of a nanotube network along with NBR phase network.     

Ribbon-like microfiber of vulcanized and non-vulcanized natural rubber obtained by the solution blow spinning

Natural rubber (NR) microfibers were obtained from NR/chloroform solutions with or without vulcanization agents, by a solution blow spinning (SBS) technique. The microfibers showed a ribbon-like morphology with average widths ranging from 15 to 45 μm, depending on the processing conditions. Concentrations of 3%, 4%, and 5% (wt/vol) of NR/chloroform were compared; at 4% wt/vol the spinning process was most stable, and fiber width was the most homogeneous. Microfibrous NR membranes incorporating vulcanizing agents were treated at temperatures of 70, 80, and 90°C for 1, 2, 3, and 4 h. Membrane tensile strength and elongation at break varied with temperature and treatment time. The best result was found with the sample treated at 90°C for 3 h. In this case, the tensile strength and elongation at break was (4.9 ± 0.8) MPa and (867 ± 18) % which is about 310% and 330% higher than the values found for the same sample without the incorporation of vulcanizing agents. This expressive increase was attributed to the vulcanization of the rubber, which also provided a shift to a higher value of the glass transition temperature. Overall properties of the blow-spun films, especially the high elasticity-contraction, suggest they are attractive candidates for use in robotics, and biobased electronics including wearable sensors.     

Vulcanization of polypropylene

Dynamic covalent crosslinking of commodity thermoplastics is a desirable target in material development, as it promises to combine the enhanced mechanical properties and thermal/solvent stability of thermosets with reprocessability and plastic flow under certain conditions activating the bond exchange. Many attempts of this development suffer from the same two problems: enhanced cost due to complex and often toxic chemicals, and the effective melt-flow index being too low for practical use. Here we return to the origins of polymer networks, and mimic the vulcanization of natural rubber in the commodity polypropylene using elemental sulfur initiated by peroxide. Forming sulfur bridges allows easy catalyst-free reprocessability based on the disulfide bond exchange. We study a broad range of compositions and reaction conditions, finding optimal balance between the crosslinking and chain scission in the melt compounder, and demonstrating much enhanced characteristics of the resulting materials. We specifically discuss and evaluate the balance between the rubber-elastic network response at high temperatures and the plastic flow enabled by disulfide exchange, responsible for the reprocessing of our vitrimers.     

Sulfuration and reversion reactions of brominated poly(isobutylene‐co‐isoprene)

The sulfuration and reversion products of brominated poly(isobutylene‐co‐isoprene) (BIIR) were characterized through the use of a model compound, brominated 2,2,4,8,8‐pentamethyl‐4‐nonene (BPMN). The reaction of BPMN with S₈ produced bisallylic polysulfides of various ranks, yielding sulfur bromide intermediates that likely contributed to the rapid oxidation of allylic sulfides into thiophenes. Reductive cure reversion to pentamethylnonene was also observed in the latter stages of vulcanization. The reaction of 2,2′‐dithiobisbenzothiazole with BIIR and BPMN produced a stable adduct that reduced the concentration of allylic bromide available for vulcanization. © 2003 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 41: 1915–1926, 2003     

Sulfur and Its Role In Modern Materials Science

Although well‐known and studied for centuries, sulfur continues to be at the center of an extensive array of scientific research topics. As one of the most abundant elements in the Universe, a major by‐product of oil refinery processes, and as a common reaction site within biological systems, research involving sulfur is both broad in scope and incredibly important to our daily lives. Indeed, there has been renewed interest in sulfur‐based reactions in just the past ten years. Sulfur research spans the spectrum of topics within the physical sciences including research on improving energy efficiency, environmentally friendly uses for oil refinery waste products, development of polymers with unique optical and mechanical properties, and materials produced for biological applications. This Review focuses on some of the latest exciting ways in which sulfur and sulfur‐based reactions are being utilized to produce materials for application in energy, environmental, and other practical areas.     

Reactive Hybrid of Polyhedral Oligomeric Silsesquioxane (POSS) and Sulfur as a Building Block for Self‐Healing Materials

This work demonstrates a new reactive and functional hybrid (S‐MMA‐POSS) of polyhedral oligomeric silsesquioxane (POSS) and sulfur prepared with a direct reaction between a multifunctional methacrylated POSS compound (MMA‐POSS) and elemental sulfur (S₈) through the “inverse vulcanization” process. S‐MMA‐POSS is an effective building block for imparting self‐healing ability to the corresponding thermally crosslinked POSS‐containing nanocomposites through a self‐curing reaction and co‐curing reaction with conventional thermosetting resins. Moreover, S‐MMA‐POSS is also a useful precursor for preparation of materials with high transparency in mid‐infrared region.

     

动态硫化工艺对EVA/EVM热塑性弹性体复合材料结构与性能的影响

使用2种动态硫化工艺制备EVA28(VA含量为28%,简称EVA)/EVA50(VA含量为50%,简称EVM)/有机蒙脱土(o MMT)复合材料.研究表明,一步法(将EVA、EVM、o MMT、过氧化物等各组分熔融共混一步动态硫化)制备的热塑性弹性体(TPV)复合材料中橡胶相(EVM相)相区尺寸为1~2μm,蒙脱土选择性的分散在橡胶相中,但剥离程度较低;与此对应,两步法(即先将EVA/EVM进行动态硫化制备热塑性弹性体,再将该动态硫化胶与o MMT熔融共混)制备的复合材料中蒙脱土在橡胶相中高度剥离,且含有蒙脱土的橡胶相尺寸仅为几百纳米.材料性能研究表明,两步法制备所得TPV复合材料具有更高的拉伸强度、拉伸模量和断裂伸长率.此外,两步法制备的复合材料还具有优异的热稳定性和显著提高的阻燃性能.     

Crosslinker Copolymerization for Property Control in Inverse Vulcanization

Sulfur is an underused by-product of the petrochemicals industry. Recent research into inverse vulcanization has shown how this excess sulfur can be transformed into functional polymers, by stabilization with organic crosslinkers. For these interesting new materials to realize their potential for applications, more understanding and control of their physical properties is needed. Here we report four new terpolymers prepared from sulfur and two distinct alkene monomers that can be predictively tuned in glass transition, molecular weight, solubility, mechanical properties, and color.