Silane grafting and moisture crosslinking of polyethylene: The effect of molecular structure

The silane grafting and moisture crosslinking of different grades of polyethylene have been investigated. Three types of polyethylene (HDPE, LLDPE, and LDPE) with different molecular structures and similar melt flow indices were selected. The initiator was dicumyl peroxide (DCP), and the silane was vinyltrimethoxysilane. The grafting reaction was carried out in an internal mixer. The extent of grafting and the degree of crosslinking were determined, and hot‐set tests were carried out to evaluate the crosslink structure of the different polyethylenes. The LLDPE had the highest degree of grafting, while the LDPE had the least. The rate of crosslinking for LDPE was higher than that of HDPE and LLDPE. The gel content of LDPE was higher than that of HDPE and LLDPE. Hot‐set elongation and the number‐average molecular weight between crosslinks (M_c) were lower for LLDPE and LDPE than for HDPE. Increasing the silane/DCP percentage led to peroxide crosslinking, thereby decreasing the M_c and hot‐set elongation. The number‐average molecular weight (M_n), molecular weight distribution, and number of chain branches were the most important parameters affecting the silane grafting and moisture crosslinking. J. VINYL ADDIT. TECHNOL., 2009. © 2009 Society of Plastics Engineers     

Silane grafting and moisture crosslinking of polypropylene

Different approaches for free‐radical initiated grafting of functional monomers to polypropylene (PP) have been investigated with a view to enabling crosslinking of the polymer upon subsequent exposure to moisture, resulting in gel contents as high as 50–60 wt%. The first approach involved grafting a co‐agent such as triallyl trimellitate (TATM) to the polymer using peroxide initiator to add carbon–carbon double bond functionality to the polymer, followed by peroxide‐initiated grafting of mercaptopropyltrimethoxysilane (MPTMS) to the PP‐TATM adduct. The second approach was the more traditional peroxide‐mediated grafting of vinyltrimethoxysilane (VTMS) to polypropylene, and was most effective at increasing melt state dynamic storage modulus. In the third approach, peroxide‐mediated grafting of VTMS was followed by peroxide‐initiated grafting of MPTMS. This process took advantage of the unsaturation created via chain scission in the first step to provide graft sites for the MPTMS in the second step. POLYM. ENG. SCI., 2011. © 2010 Society of Plastics Engineers     

Silane grafting and moisture crosslinking of polypropylene

Peroxide initiated vinylsilane grafting of polypropylene in an intensive mixer, and the subsequent water crosslinking process were studied. Different concentrations of vinyl trimethoxysilane and dicumyl peroxide were used. The materials obtained after mixing in the rheocord were hot pressed at 190°C. The melt viscosity of the obtained sheets, the melting enthalpy and melting temperature (DSC, differential scanning calorimetry), the mechanical properties and the thermal decomposition behavior (TG, thermogravimetric analysis) were studied. No evidence of grafting during the rheocord processing was observed. Nevertheless, for the hot pressed sheets with concentrations higher than 4 phr of vinyl silane an important increase in the melt viscosity was observed. This increase agrees with the change observed in the mechanical properties, which show a maximum for the water crosslinked samples containing 4 phr of vinyl silane. The modulus increases by 39% at 90°C and 33% at 130°C, while the tensile strength rises by ～22% at both temperatures. The silane grafted water crosslinked samples show a more stable thermal behavior than both the silane grafted samples and the unmodified polypropylene.     

Assessment of oxidative thermal degradation of crosslinked polyethylene and ethylene propylene rubber cable insulation

This paper presents procedures to monitor oxidation degradation of two commonly used cable insulations, crosslinked polyethylene (XLPE) and ethylene propylene rubber (EPR). Since the techniques described require only micro specimens, deterioration of cable insulation can be monitored without destroying the function of the cable. The techniques described are melting point, crystallinity, infrared carbonyl absorbance, gel content, relative hardness, and differential scanning calorimetry (DSC) oxidation induction time. The techniques were applied following accelerated aging over a period in excess of two years. The results from the micro specimens were directly related to embrittlement and the decrease in ultimate elongation. The previous thermal history of XLPE was determined using DSC melting peak analysis.     

Aspects of the crosslinking of polyethylene with vinyl silane

The crosslinking reaction of low‐density polyethylene with vinyl triethoxysilane was studied in great detail. The effects of a wide range of concentrations (0–27.33 phr silane and 0–1.25 phr benzoyl peroxide) on the mechanical properties, hot‐set testing, gel contents, and burning behaviors of the resulting crosslinked polyethylene were studied. The effect of variations in the concentration of silane was found to be a dictating parameter for all these properties. Moreover, at or above a certain threshold concentration of silane (4.56 phr), samples not only qualified for hot‐set testing but also showed other properties at an optimum level. © 2004 Wiley Periodicals, Inc. J Appl Polym Sci 92: 3796–3803, 2004     

Effects of termonomers on crosslinking rate and crosslinking structure of ethylene propylene terpolymers

Study was made concerning both the rate of crosslinking and the structure of crosslinks of terpolymers that have dicyclopentadiene, 1, 4–hexadiene, methylene norbornene, and ethylidene norbornene for termonomers so as to look into the role of termonomers during crosslinking of ethylene propylene terpolymers. In the study, activation energy and frequency factor, both apparent were determined by the rate constant of crosslinking and differences in crosslinks were analyzed following both chemical and physical methods. Infrared analysis into the volume of consumption of double bond was adopted to examine the manner of crosslinking. In respect to the magnitude of the rate constant, ethylidene norbornene came in first being followed by 1,4-hexadiene, methylene norbornene, and dicyclopentadiene. The structure of termoners affected the apparent activation energy and the apparent frequency factor was subject to the influences of said structure and others including the variation in the degree of unsaturation. During the early stage of crosslinking, the formation of the crosslink of polysulfide-type was paramount to all others and the speed of conversion therefrom either to disulfide–type or to monosulfide varied with the kind of terpolymers and was in proportion to the rate constant of crosslinking.     

Effect of some curatives on the properties of ethylene propylene diene rubber/polyethylene blends

A series of ethylene propylene diene rubber/polyethylene (EPDM/PE) blends has been prepared containing different weight fractions of PE up to 0.66. The blends were vulcanized with a sulphur system N-cyclohexyl-2-benzthiazol sulphenamide/sulphur (CBS/S), and a non-sulphur-system dicumyl peroxide (DCUP). The concentration of the latter has been changed from 1.5 phr up to 6 phr calculated on the total weight of the blend composition. It has been found that the maximum torque obtained from rheographs for blends vulcanized with the CBS/S system decreases markedly with increasing PE concentration in comparison with those vulcanized with peroxide. The E modulus obtained from the stress–strain diagram at 110 °C showed the role played by the crosslinking of PE, the E modulus for blends vulcanized by peroxide being higher than for samples vulcanized with CBS/S. In contrast, the values of E modulus of both samples are practically the same at room temperature and attain more than 40 MPa depending on the composition. The tensile strength at room temperature strongly increases with increasing the weight fraction of PE. It has also been confirmed that the melting point of the crystalline phase of PE decreases with increasing crosslinking density of PE. The shear modulus obtained from dynamic mechanical measurements is in accordance with that obtained from static mechanical measurements. © 1999 Society of Chemical Industry     

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

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

Chemical reactions in crosslinking of copolymers of ethylene and vinyltrimethoxy silane

The crosslinking reactions of a new type of polyethylene, an ethylene vinyltrimethoxy silane (EVS) copolymer, when reacted with water has been studied. Samples of EVS were treated in water at 90°C. The kinetics of the crosslinking was followed by measuring the gel content and by determination of the content of different structures (? Si? OCH₃,? Si? OH, and ? Si? O? Si? ) using FT-IR. The observations show that a maximum gel content of 70-75% is obtained after 25 h treatment in water at 90°C. On the other hand, the absorption index for the crosslinks, ? Si? O? Si? , continues to increase until about 100 h, i.e., more crosslinks seem to be formed without a simultaneous increase in gel content. Mechanical measurements showed decreased elongation at break even after very long treatments. Thermo-oxidative degradation is, however, also responsible for the change in mechanical properties. For properly stabilized samples, the decrease in elongation leveled off after about 100 h of treatment. This indicates that the crosslinks formed after 25 h mainly should be within the already existing gel. The observed synergistic effect of crosslinking and thermo-oxidative degradation emphasizes the importance of a proper stabilizing system.     

Styrene‐assisted melt free radical grafting of glycidyl methacrylate onto an ethylene and propylene rubber

This article deals with the efficiency of using styrene (St) as a comonomer to promote the melt free radical grafting of glycidyl methacrylate (GMA) onto an ethylene and propylene rubber (EPR) in a batch mixer and a corotating self‐wiping twin screw extruder. The addition of St to an EPR/GMA/peroxide system increases not only GMA's grafting yield but also its grafting rate. The time required for the EPR/GMA/peroxide system without St to reach a given amount of grafted GMA is at least 10 times that needed for the same system in the presence of an equimolar amount of St. For example, about 60 min are required for the EPR/GMA/dicumyl peroxide (composition: 100/3.0/0.3 by weight) to reach 1.5 phr (parts per hundred resin) GMA (i.e., 1.5 g grafted GMA per 100 g EPR). The same amount of grafted GMA is reached in < 3 min when 3.0 phr St is charged to the system. This significant reduction of reaction time is crucial for a successful free radical grafting of GMA on EPR in a corotating twin screw extruder, because the residence time in such a machine is typically on the order of 0.5–5 min. © 1999 John Wiley & Sons, Inc. J Appl Polym Sci 71: 125–133, 1999     

乙丙橡胶的生产、应用及需求

乙丙橡胶有二元和三元之分：二元为乙烯和丙烯的共聚物，三元为乙烯、丙烯和二烯类第三单体（非共轭二烯烃）的共聚物。三元乙丙橡胶因单体不同，分为多种类型。乙丙橡胶与天然橡胶、丁苯橡胶相比，有卓越的耐候性、耐臭氧性和耐热老化性；与硅橡胶、氟橡胶等特种橡胶相比...     

乙丙橡胶生产技术及应用进展

介绍了国内外乙丙橡胶的开发现状、生产技术及应用进展，对我国乙丙橡胶的发展提出了建议。     

茂金属催化剂在乙丙橡胶中的应用

概述了乙丙橡胶用茂金属催化剂的研究现状及进展，介绍了茂金属乙丙橡胶的生产情况和已经工业化的工艺路线及其特点。     

活性阴离子接枝法制备乙丙橡胶与苯乙烯接枝聚合物SEP的研究

具有良好低温性能的润滑油粘度指数改进剂已经成为国内润滑油市场亟待开发的产品.以乙丙橡胶和苯乙烯为原料,采用活性阴离子接枝法制备SEP用作润滑油粘度指数改进剂,通过红外吸收光谱、核磁共振氢谱、凝胶渗透色谱进行表征分析,证实其分子结构和氢化后的SIS基本相似.其性能测试表明,SEP具有良好的低温性能.     

Kinetics of crosslinking of linear polyethylene with t-butyl peroxide

The kinetics of the curing of polyethylene with di-t-butyl peroxide have been studied using a Wallace-Shawbury curometer and a Monsanto rheometer. Results obtained for the activation energy of the crosslinking reaction are of comparative value only, because the temperature of the specimen is not known with sufficient accuracy; this applies especially to the rheometer. It was not possible to crosslink polyethylene premixed with carbon black; the addition of carbon black to the mixture of polyethylene and peroxide greatly reduced the degree of crosslinking obtained.     

全球乙丙橡胶发展概况及其专利分析

通过对乙丙橡胶专利文献的分析,揭示了该领域的发展趋势、地域分布和申请人的专利保护情况。介绍了在生产工艺、催化体系和产品开发方面的研发热点,从专利发明和保护的角度提出了建议。     

Fracture behaviors of metallocene‐catalyzed polyethylene elastomer via silane crosslinking

Silane moisture‐cured metallocene‐catalyzed polyethylene (mPE) to form an elastomer has been prepared. Metallocene polyethylenes with two different levels of comonomer contents were grafted with various amounts of vinyltriethoxy silane. “Threshold” fracture energy is roughly proportional to the reciprocal square root of Young's modulus. By relating tensile strength to tear strength, the corrected average depth of flaw is in the range of 40.5 ± 11.0 μm, which successfully confirms the extension of conventional elastomeric theory to the low crystalline vulcanizates under some limitations. The cutting strength of mPE vulcanizates gives an intermediate value when compared with crystalline plastics and conventional elastomer, and is comparable with other evaluations of cutting strength for different types of materials, which further signifies the importance of crystalline yielding even in the nano‐fracture zone of deformation. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 101: 2472–2481, 2006     

乙丙橡胶技术的专利文献分析

通过对乙丙橡胶专利文献的检索与分析,重点介绍了美国Exxon公司的技术发展路线,从催化体系、生产工艺、产品开发角度解析了该公司的研发热点和专利布局,结合我国的研究开发情况探讨了乙丙橡胶的发展方向,并从专利角度提出了建议。     

Studies on dynamic and static crosslinking of ethylene vinyl acetate and ethylene propylene diene tercopolymer blends

The effect of blend ratio on the crosslinking characteristics of ethylene vinyl acetate and ethylene propylene diene tercopolymer (EVA‐EPDM) blends was studied by differential scanning calorimetry and a torque rheometer (Rheocord‐90). The activation energy decreases with an increase in EVA content in the blend. The cure rate increases whereas the optimum cure time and energy consumption for curing decrease with an increase in the EVA/EPDM ratio. The dynamic curing obtained by the torque rheometer is very fast compared to the static curing obtained by differential scanning calorimetry. © 1999 John Wiley & Sons, Inc. J Appl Polym Sci 74: 2756–2763, 1999