Performance evaluation of silane crosslinking of metallocene‐based polyethylene–octene elastomer

Vinyl trimethoxysilane (VTMS) was grafted onto metallocene‐based polyethylene–octene elastomer (POE) using a free‐radical reaction of VTMS and dicumyl peroxide as an initiator, and then the grafted POE was crosslinked in the presence of water. The effects of VTMS concentration on crystallization behavior, mechanical properties, and thermal properties of POE before and after crosslinking were studied in this article. Multiple melting behaviors were found for POE after silane crosslinking by using DSC measurement. Degree of crystallization of silane‐crosslinked POE decreases from 18.0 to 14.3%, with increase of VTMS from 0 to 2.0 phr. Tensile strength of silane‐crosslinked POE reaches a maximum of 28.4 MPa when concentration of VTMS is 1.5 phr, while elongation at break is 487%. TG shows that the temperature of 10% weight loss for pure POE is 405°C, while for crosslinked POE with addition of 2.0 phr VTMS the value comes to 452°C, indicating that crosslinking significantly help improve the thermal stability of POE. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 102: 5057–5061, 2006     

Thermal and mechanical properties of silane‐grafted water crosslinked polyethylene

The effects of linear low density polyethylene (LLDPE) grafting with vinyltrimethoxysilane by different types and contents of peroxide were studied. When grafting silane onto LLDPE, with 0.10 phr of Dicumyl peroxide (DCP) or 0.05 phr content of 2,5‐Dimethyl‐2,5‐di (tert‐butyl‐peroxy)‐hexane (DHBP), it was found that the grafting effect was improved; however, as Di(2‐tert‐butylperoxypropyl ‐(2))‐benzene (DIPP) or excess DHBP was used, LLDPE was supposed to cause self‐crosslinking, which reduced the grafting effect of silane and was invalid in the processing of extrusion. In this study, vinyl trimethoxysilane (VTMS) was grafted onto various polyethylenes (HDPE, LLDPE, and LDPE) using DCP as an initiator in a twin screw extruder. The grafted polyethylenes were able to crosslink utilizing water as the crosslinking agent. The effects of varied crosslinking time on the mechanical properties of the crosslinked polyethylenes were studied. It was found that the HDPE and LLDPE were apt to crosslink during the grafting process and thus decreased the grafting ratio. Multiple melting behavior was observed for crosslinked LDPE and LLDPE. Mechanical and thermal properties of the crosslinked PE are much better than that of uncrosslinked PE. © 2005 Wiley Periodicals, Inc. J Appl Polym Sci 96: 2383–2391, 2005     

硅烷接枝交联HDPE、LLDPE及其共混物的结构研究

利用红外光谱、差示扫描量热法等方法研究了高密度聚乙烯(HDPE)、线性低密度聚乙烯(LLDPE)及其共混物的乙烯基三乙氧基硅烷(VTEOS)接枝及交联产物的分子结构、熔融行为。结果表明,VTEOS接枝交联PE能力为:LLDPE>HDPE/LLDPE共混物>HDPE;接枝和交联使HDPE、LLDPE及其共混物的结晶度和熔点降低,晶粒变得不均匀。     

Preparation of crosslinked and thermostable paste poly(vinyl chloride)

The grafting of a mercaptoalkyltrialkoxysilane onto an activated poly(vinyl chloride) (PVC) paste resin with subsequent hydrolytic crosslinking has been studied. The resins were prepared by copolymerization of vinyl chloride monomer and glycidylmethacrylate (GMA). The grafting of a mercaptosilane was carried out during gelation of the plastisol. In this step the formation of a chemical network was avoided. By steaming at 120°C for 30 min the grafted samples crosslinked. The gel yield increased with increasing fraction of GMA and up to a given level with the fraction of the mercaptosilane. When using a resin of PVC homopolymer no crosslinking occurred. The silane grafted and crosslinked samples were found to have satisfactory thermal stability. © 1998 John Wiley & Sons, Inc. J Appl Polym Sci 67:849–853, 1998     

硅烷接枝温水交联天然橡胶的研究

以多功能乙烯基硅烷为接枝单体,过氧化苯甲酰为引发剂,通过熔融混炼接枝和温水交联分别制备了硅烷接枝天然橡胶和交联硅烷接枝天然橡胶。采用傅里叶红外光谱仪和扫描电子显微镜分别对硅烷接枝天然橡胶和交联硅烷接枝天然橡胶进行了表征,并研究了接枝单体及引发剂的用量、接枝和交联工艺（温度和时间）等对交联硅烷接枝天然橡胶凝胶含量的影响,同时研究了不同凝胶含量对交联硅烷接枝天然橡胶力学性能的影响。结果表明,天然橡胶发生了硅烷接枝和交联反应;随着接枝单体及引发剂用量、混炼时间和温度以及交联温度和时间的增加,交联硅烷接枝天然橡胶的凝胶含量单调增加;交联硅烷接枝天然橡胶的力学性能随着凝胶含量的增加而明显得到改善,凝胶含量为80%的交联硅烷接枝天然橡胶的拉伸强度比纯天然橡胶提高了30%,断裂伸长率提高了8.5倍。     

A reactive extrusion process for the free radical grafting of silanes onto polypropylene: Effects of processing conditions and properties of water cross‐linked silane‐grafted polypropylene

Silane grafting and water cross‐linking of polypropylene (PP) are a recent method to modify its properties, such as melt strength, heat, and chemical resistance. This work aims at grafting silanes onto PP by reactive extrusion. The occurrence of the grafting of silane onto PP was confirmed by Fourier transform infrared (FTIR) and a method based on FTIR was developed to quantify the amount of polymerized silane and that of silane grafted onto PP. The molar mass of the silane‐grafted PP and its melt viscosity were also measured. A multiobjective optimization strategy was used to study the effects of processing conditions on the quality of the silane‐modified PP. It was concluded that to maximize the amount of silane grafted on PP and minimize the amount of polymerized silane and the decrease in PP chain scission, screw speed and barrel temperature should be low and feed rate high. POLYM. ENG. SCI., 2013. © 2013 Society of Plastics Engineers     

Structure and properties of a poly(amino ether) resin after reprocessing in the melt state

The effects of reprocessing by extrusion for up to five cycles, at both the usual (200°C) and an extreme (230°C) temperature, on the structure and mechanical properties of a poly(amino ether) (PAE) resin were studied. A slight darkening and viscosity increase was observed, mainly upon reprocessing at 230°C. The melt flow index and solubility analysis indicated that grafting and crosslinking reactions took place, respectively, after reprocessing at 200 and 230°C. The Young′s modulus and the yield stress of PAE increased slightly with successive extrusion cycles. This was attributed to the viscosity‐induced increase in orientation, and to a minor extent to the partially grafted/crosslinked nature of the samples. The decrease in the ductility was more noticeable in the samples reprocessed at 230°C, and was attributed to the reduced ability to elongate of partially grafted and partially crosslinked structures present after reprocessing, respectively, at 200 and 230°C. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 101: 1368–1373, 2006     

Effect of silane‐grafting on water tree resistance of XLPE cable insulation

Water treeing is one of the main deterioration phenomena observed in the polymeric insulation of extruded crosslinked polyethylene (XLPE) cables, which can affect the service life of power cables. In this work, we investigated the effect of grafting of a silane (vinyl trimethoxysilane, VTMS) on the resistance of XLPE to water treeing. A series of water‐treeing tests, the mechanical and dielectric measurements indicated that the silane‐grafting could significantly improve the water tree resistance of the conventional XLPE cable insulation with little influences on its dielectric properties, e.g., the dielectric breakdown strength, dielectric constant and loss tangent, and its mechanical performance. It was found that there exists an optimum value of VTMS concentration (about 0.6 phr) corresponding to the minimum water tree length. The water tree resistance mechanism of silane‐grafted XLPE was proposed on the basis of the process of silane hydrolysis and crosslinking. © 2009 Wiley Periodicals, Inc. J Appl Polym Sci, 2010     

交联玉米淀粉-醋酸乙烯酯接枝共聚乳液的制备及性能

碱性条件下,玉米淀粉经环氧氯丙烷交联处理后,在引发剂存在下,与醋酸乙烯酯进一步接枝共聚制得了交联玉米淀粉-醋酸乙烯酯乳液,经红外光谱确认了共聚物,较好的乳液制备工艺:m(淀粉)∶m(环氧氯丙烷)=25∶1,90°C交联1 h,加入过硫酸铵,按m(醋酸乙烯酯)∶m(淀粉)=3∶1,在70°C接枝共聚3 h。各种淀粉胶液的性能对比结果表明:交联玉米淀粉-醋酸乙烯酯接枝聚合乳液冷热稳定性好,耐水性≥54 h,储存期360 d,剪切强度达9.1 MPa。     

Influence of grafting formulations and extrusion conditions on properties of silane‐grafted polypropylenes

The melt grafting of unsaturated silanes onto powdered polypropylene (PP) in a Haake TW100 twin‐screw extruder and curing in hot water were studied. The influence of grafting formulations and extrusion conditions on the melt flow rates of grafted PP and the gel percentages of crosslinked PP was investigated. The gel percentages of methacryloylpropyltrimethoxysilane (VMMS)‐grafted PP were markedly higher than those of vinyltriethoxysilane (VTES)‐ and vinyltrimethoxysilane (VTMS)‐grafted PP, while significantly less degradation of PP during grafting was observed for VMMS‐grafted PP. When benzoyl peroxide (BPO) was used as an initiator, no degradation of PP during grafting was observed, and the melt flow rates of grafted PP decreased with increasing BPO concentration. In contrast, use of dicumyl peroxide (DCP) as an initiator resulted in severe degradation of PP, and the melt flow rates of grafted PP increased gradually with increasing DCP concentration. BPO resulted in higher gel percentages than those of DCP at a fixed initiator concentration. Introduction of styrene into the grafting system greatly improved the gel percentage of crosslinked PP and reduced the degradation of PP during grafting. The optimum molar ratio of styrene to monomer is at about 1.5:1. Relatively low processing temperatures and high screw speeds are favorable. © 2000 John Wiley & Sons, Inc. J Appl Polym Sci 78: 1233–1238, 2000     

Comparative study of the effects of chlorinated polyethylene and acrylic impact modifier on the thermal degradation of poly(vinyl chloride) compounds and poly(vinyl chloride)/(oil palm empty fruit bunch) composites

The effects of chlorinated polyethylene (CPE) and acrylic impact modifier (AIM) on the thermal degradation of poly(vinyl chloride) (PVC) compounds and composites were investigated. The amounts of AIM and CPE used were fixed at 9 parts per hundred parts of resin (phr), while oil palm empty fruit bunch (OPEFB) fiber content was increased from 0 to 40 phr. To produce composites, the PVC formulations were dry‐blended by using a laboratory blender before being milled into sheets on a two‐roll mill at 165°C. The milled sheets were then hot‐pressed at 180°C. The thermal degradation of the specimens was evaluated by using thermogravimetry in a nitrogen environment. Thermal stability of the PVC/CPE compounds and PVC/CPE/OPEFB composites was improved by the addition of CPE. The CPE retarded the dehydrochlorination of PVC. However, the stabilization effect was reduced by the incorporation of OPEFB at levels of 30 and 40 phr. The presence of AIM accelerated the dehydrochlorination of PVC/AIM compounds and PVC/AIM/OPEFB composites. J. VINYL ADDIT. TECHNOL., 2010. © 2010 Society of Plastics Engineers     

Crosslinkable polypropylene composites made by the introduction of silane moieties

Silane‐crosslinkable polypropylene (PP) composites containing calcium carbonate (CaCO₃) as a filler have been investigated. The melt grafting of vinyl trimethoxysilane to PP with dicumyl peroxide (DCP) as a radical initiator is demonstrated. The thermal and mechanical properties of the crosslinkable products are also discussed. The results show that two reactions, that is, silane grafting and PP degradation, take place in parallel. The extents of silane grafting and PP degradation strongly depend on the reaction temperature, grafting formulation, and amount of the filler in the systems. Increasing the DCP concentration (up to 0.05 wt %) leads to an increase in the grafting degree. However, when the concentration of radicals is over a certain degree, the dominant reaction is PP chain scission. This results in a drastic decrease in the polymer viscosity. In systems containing both silane and CaCO₃, the viscosity of the polymer is higher than that of a grafted sample without CaCO₃ addition; in other words, the effect of the filler on the polymer viscosity compensates for the effect caused by PP degradation. Differential scanning calorimetry results show that the crystallization starts earlier for grafted samples. The percentage of the crystallinity of grafted PP is higher than that of the pure polymer. The incorporated silane does not have a strong effect on the mobility of the PP chains, as revealed by dynamic mechanical analysis. In comparison with ungrafted composites, the silane‐crosslinkable products show higher tensile stress and modulus. © 2005 Wiley Periodicals, Inc. J Appl Polym Sci 97: 1476–1483, 2005     

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     

Mechanical and thermal properties of blends of low‐density polyethylene and ethylene vinyl acetate crosslinked by both dicumyl peroxide and ionizing radiation for wire and cable applications

Formulations of chemically crosslinked and radiation‐crosslinked low‐density polyethylene (LDPE) containing an intumescent flame retardant such as ammonium polyphosphate were prepared. The influence of blending LDPE with a poly(ethylene vinyl acetate) copolymer (EVA) and the effects of various coadditives, including polyethylene grafted with maleic anhydride (PEgMA), vinyl silane with boric acid, and talc, on the mechanical and thermal properties were investigated. Chemical crosslinking by dicumyl peroxide and crosslinking by ionizing radiation from an electron‐beam accelerator were both used and compared. Improved mechanical properties were observed by the partial replacement of LDPE with EVA. Similar mechanical or thermal properties were observed with coadditives such as PEgMA and vinyl silane with boric acid. The addition of a small amount of talc improved the tensile strength of the formulations. All crosslinked formulations showed good thermal stability on the basis of the retention of mechanical properties after thermal aging for 168 h at 135°C and a hot‐set test. © 2007 Wiley Periodicals, Inc. J Appl Polym Sci, 2008     

Properties of polypropylene structural foam crosslinked by vinyltrimethoxy silane

Polypropylene containing the blowing agent azodicarbonate was first grafted with vinyl trimethoxy silane, then crosslinked using the hot water treatment. Two heating stages initiated the blowing agent and formed polypropylene structural foam. The effects of such reaction variables as initiator, cross-linking agent, cross-linking accelerator, and blowing agent on the gel fraction, density, and expansion ratio of polypropylene foam were studied. Furthermore, cell dimension, compression strength, and volume resistivity were also measured and analyzed.     

Mechanical Properties of Benzoylated Oil Palm Empty Fruit Bunch Short Fiber Reinforced Poly(vinyl chloride) Composites

The influence of untreated and benzoylated oil palm empty fruit bunch (OPEFB) short fiber loading on the mechanical properties of the poly(vinyl chloride) (PVC) composite was studied. Benzoylated OPEFB was produced by mixing OPEFB with NaOH solution and agitating vigorously with benzoyl chloride. The PVC resin, various additives, and OPEFB were first dry blended using a laboratory mixer before being milled into sheets on a two-roll mill at 165°C and then hot pressed into composite samples at 180°C. The tensile and impact strength of untreated and benzoylated OPEFB composites decreased whereas the tensile modulus increased with increasing fiber loading from 0 to 40 phr. However, the benzoylated OPEFB was able to improve the tensile properties and impact strength of composites when compared to the untreated fiber. The enhancement of mechanical properties showed that the treatment improved the OPEFB fiber-PVC matrix interfacial adhesion. The improvement of adhesion was clarified by SEM micrographs, the increase of water resistance, and the reduction of glass transition temperature of the composites.     

Silane grafting reactions of LDPE,HDPE, and LLDPE

Vinyl trimethoxysilane and vinyl triethoxysilane grafting reactions, induced by dicumyl peroxide, of LDPE, HDPE, and LLDPE were investigated. The apparent activation energy of vinyl trimethoxysilane grafting reactions was positive when the reactions were induced by 0.2 phr of the peroxide. The apparent activation energies were negative when 0.05, 0.1, 0.15, and 0.25 phr of peroxide were used. The extents of vinyl trimethoxysilane grafting reactions of polyethylenes were in the order of LLDPE > LDPE > HDPE, although the extents of peroxide cross‐linking were in the order of LDPE > LLDPE > HDPE. As compared with vinyl trimethoxysilane, vinyl triethoxysilane produced a relatively high extent of grafting reactions of LDPE but showed a relatively low rate of water cross‐linking reactions of the silane‐grafted LDPE. The investigation of effects of the amount of peroxide on the vinyl trimethoxysilane grafting reaction heats demonstrated that the extent of silane grafting reactions increased proportionally as peroxide was increased until a certain amount (the value was dependent on the amount of silane used). Beyond this amount of peroxide, the silane grafting did not increase, whereas the peroxide cross‐linking appeared to increase significantly with increasing amounts of peroxide. © 1999 John Wiley & Sons, Inc. J Appl Polym Sci 74: 3404–3411, 1999     

Thermal properties of silane-grafted water-crosslinked polyethylene

Vinyl trimethoxysilane grafting reactions of low-density polyethylene (LDPE) were performed in an extruder, followed by crosslinking with boiled water. The thermal properties of both silane-grafted and silane-grafted water-crosslinked LDPE were investigated using differential scanning calorimetry (DSC) and thermogravimetric analysis (TGA). DSC data showed that the silane grafts on the LDPE molecules were thermal stable in the absence of moisture under 130°C under which the silane-grafted LDPE could be processed or recycled. The silane grafts on the LDPE molecules reduced the melting point of LDPE and gave rise to an endotherm shoulder at about 85°C. TGA data showed that the decomposition temperature of the silane-grafted LDPE was much higher than that of LDPE. It was demonstrated that the cause of the increase in the decomposition temperature was not due to the silane grafts but due to the peroxide-induced crosslinking reactions during the silane grafting reactions performed in an extruder. Silane-grafted water-crosslinked LDPE displayed multiple melting behavior resulting from phase separation during crosslinking of LDPE with water. The phase separation gave rise to two melting points, including one at about 94°C, and the other at about 107°C. © 1998 John Wiley & Sons, Inc. J. Appl. Polym. Sci. 70: 1075–1082, 1998     

Flame retardation of polypropylene: Effect of silane treated antimony compounds

Flame retardation of polypropylene was accomplished by blending with antimony compounds (Sb₂O₃ and SbPO₄) in conjunction with polyvinyl chloride (PVC) or ferric oxide. The compatibility and dispersion of antimony compounds in the polymer matrix was enhanced by using silane coupling agents, viz., vinyltriethoxysilane (A-151) and γ-aminopropyltriethoxysilane (A-1100). Rheological properties of filled polypropylene were studied in the temperature range 180 to 220°C at shear rates of 29.5 to 119.5 sec^?1. An increase in the melt viscosity was found in the filled polypropylene as compared to virgin polymer. Silanation of antimony compounds also influenced the melt rheology of flame retardant polypropylene. Incorporation of 6 phr Sb₂O₃ and 19 phr PVC raised the oxygen index of polypropylene to 22.9 and this sample was found to be self extinguishing in 65 s with a burning rate of 0.06 mm/s as compared to 1.1 mm/s for unfilled polypropylene. Though silanation of antimony compounds slightly reduced the oxygen index of flame retardant polypropylene, yield strain and flexural rigidity of injection molded samples was improved over unsilanated flame retardant polymer.     

Thermal and crystallization behavior of silane‐crosslinked polypropylene

Silane‐crosslinked polypropylene (PP) has been prepared first by the grafting of silane onto the backbone of PP in a melt process and then by crosslinking in warm water. The effects of type and concentration of silane and peroxide on the silane grafting on PP were investigated. The thermal behavior of the silane‐crosslinked PP was studied by thermogravimetric (TG) and differential scanning calorimetry (DSC) methods. TG results show that PP prepared via silane crosslinking increases its thermal stability greatly. It has been found from DSC measurements that the crystallization temperatures, ie the onset temperature and peak temperature of the exotherm of the silane‐crosslinked PP, increase compared with those of the pure PP. The silane crosslinking hardly changes the crystallinity degree of PP. The crystallization behavior of the silane‐crosslinked PP was also studied by wide‐angle X‐ray diffraction analysis. Copyright © 2004 Society of Chemical Industry