交联聚乙烯的应用及技术进展

对交联聚乙烯(CLPE)的应用情况及生产技术的发展概况进行了综述，并从交联原理和生产工艺等方面对辐射交联、紫外光交联、过氧化物交联和硅烷交联等CLPE生产方法进行了对比介绍。由于硅烷交联和过氧化物交联比较容易实现且投资相对较少而被广泛应用，而辐射交联和紫外光交联对厚制品很难实现均匀交联，仅限于薄制品领域。建议国内相关单位加大专用料的研制开发力度，在提高塑料加工设备的精度和水平上多做工作。     

高密度聚乙烯/低密度聚乙烯复合交联特性

采用转矩流变仪考察了高密度聚乙烯／低密度聚乙烯在有机过氧化物存在下的交联过程，对比了不同原料配比制取的交联物的微观结构形态及熔融结晶特性，同时针对典型交联物采用莫志深法考察了其结晶动力学。结果表明．原料配比、引发剂浓度以及添加二氧化硅对交联物的微观结构和性能具有显著的影响。选择合适的原料配比和交联工艺，可以获得相对完善的网络交联结构。     

聚氯乙烯交联方法的研究进展

介绍了聚氯乙烯(PVC)的几种交联方法及其进展,包括辐射交联、化学交联、共混交联和PVC改性交联,重点讨论和对比了用过氧化物、硅烷和三嗪类化合物作交联剂的PVC化学交联,并指出共混交联法是最有前途的PVC交联方法.     

EVM橡胶过氧化物交联体系的研究

研究了交联剂过氧化二异丙苯(DCP)、双叔丁基过氧异丙基苯(BIPB)、2,5-二甲基-双(叔丁基过氧基)己烷(DBPMH)以及助交联剂三烯丙基异氰脲酸酯(TAIC)、三烯丙基氰脲酸酯(TAC)、N,N′-间苯撑双马来酰亚胺(HVA-2)对乙烯-醋酸乙烯酯橡胶(EVM)硫化特性、交联密度以及力学性能的影响。通过测试硫化曲线、力学性能和交联密度还研究了无机阻燃填料氢氧化镁的隔离效应对EVM橡胶交联效率的影响。结果表明,EVM橡胶最优过氧化物交联体系为BIPB和TAIC,其最佳配比为2.3/2.5,此时EVM橡胶有较好交联效率、交联速率和力学性能。氢氧化镁对EVM橡胶的交联效率没有影响,但硅烷化氢氧化镁能够提高EVM橡胶的表观交联密度。使用高交联效率过氧化物交联体系BIPB和TAIC,并添加硅烷化氢氧化镁,可平衡EVM橡胶阻燃性能和力学性能。     

Cure and scorch in the processing of ethylene‐propylene‐diene terpolymer (EPDM)

The objective of this work is to ascertain the characteristics of desirable (cure) and especially undesirable (scorch) crosslinking when carbon black filled ethylene propylene diene terpolymer (EPDM) is processed using different peroxide initiators. The mixing temperature and the nature of the peroxide initiator are crucial parameters affecting scorch (undesirably premature crosslinking) in this rubber. Processability and properties of EPDM prepared using various mixer set temperatures have been investigated. Dicumyl peroxide (Luperox DC), di(t‐butylperoxy) diisopropylbenzene (Luperox F), and 2,5‐dimethyl‐2,5‐di(t‐butylperoxy) hexane (Luperox 101) were used as crosslinking initiators. Higher mixing temperatures give shorter scorch times, greater scorch magnitudes, greater heterogeneities in crosslink spatial distribution and poorer tensile properties. However, extreme localization of the unwanted crosslinking at the rubber‐filler interface does have a beneficial effect. Luperox DC offers poorer processability and poorer resulting properties than do Luperox F and Luperox 101, due to its shorter half‐life and greater solubility in the rubber phase. This is the first time that the spatial heterogeneity of crosslinking and scorch has been related to the basic thermodynamics of 3‐component 2‐phase systems. © 2016 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2017 , 134, 44523.     

Peroxide crosslinking of unplasticized poly(vinyl chloride)

A crosslinking system consisting of 1,1‐di‐t‐butylperoxy‐3,3,5‐trimethyl cyclohexane peroxide and trimethylolpropane trimethacrylate (TMPTMA) has been used to introduce crosslinks into unplasticized poly(vinyl chloride) (PVC). The influence of the concentration of both reagents has been investigated, and crosslinking monitored by determination of the remaining sample weight after Soxhlet extraction with tetrahydrofuran. The system used (i.e., 0.5–2.0 phr peroxide with 5 to 15 phr TMPTMA) has been shown to be effective for crosslinking PVC. Gel contents of 30–40% have been obtained, premature crosslinking during processing is largely avoided, but thermal stability still needs to be improved. Considerable improvements in elevated temperature mechanical properties can be attained using an appropriate TMPTMA/peroxide concentration. The best tensile properties were obtained with 0.5 phr peroxide and 15 phr TMPTMA. Observed increases in T_g, also achievable with only 0.5 phr peroxide, but only slightly dependent on TMPTMA concentration, represent a useful increase in service temperature for the resulting compound. Lower peroxide levels may be adequate to achieve property improvements. © 2000 John Wiley & Sons, Inc. J Appl Polym Sci 77: 2657–2666, 2000     

Effect of peroxide crosslinking on the dynamic modulus of silicone rubber

The effect of peroxide crosslinking on the dynamic modulus of a silica‐reinforced silicone [poly(dimethylsiloxane)] elastomer was investigated. Three different peroxides (t‐butyl peroxide, t‐butyl perbenzoate, and benzoyl peroxide) were employed at various practical loadings and differences in the nonlinear behavior of the dynamic modulus were found. Results are discussed with respect to changes in crosslinking density and the identity of the peroxide. © 2005 Wiley Periodicals, Inc. J Appl Polym Sci 97: 1504–1512, 2005     

Preparation of granular crosslinkable medium‐density polyethylene

Granular crosslinkable medium‐density polyethylene (XLPE) without scorch inhibitor was prepared adding organic peroxide [2, 5‐dimethyl‐ 2, 5‐ di‐ (t‐butyl‐peroxy) hexyne‐3] through extrution process, in industrial scale. Twin screw extruder was used to mix the polyethylene and the peroxide. The temperature zones of the extruder were controlled very carefully to prevent unwanted crosslinking during extrusion. Compression molding, rotational molding, and injection molding of XLPE at 155°C made no crosslinking in PE, and then they were exposed to higher temperatures at which the organic peroxide decomposed to provide free radicals which led to the crosslinking of the MDPE. The thermal properties (using dynamic mechanical analysis, DMA, differential scanning calorimetric analysis, DSC, and thermogravimetric analysis, TGA, techniques) and mechanical properties (including strain at break and stress at break) of virgin PE, crosslinkable PE, and crosslinked PE have been compared. The crossliked PE and virgin PE were also studied by X‐ray diffraction (XRD) technique. © 2007 Wiley Periodicals, Inc. J Appl Polym Sci 104: 1873–1879, 2007     

Crosslinking of high‐density polyethylene in the presence of organic peroxides

The crosslinking efficiency of various commercially available organic peroxides (dicumyl peroxide, O,O‐t‐butyl O‐2‐ethylhexylperoxycarbonate, t‐butyl peroxybenzoate, t‐butyl 3,5,5‐trimethylperoxyhexanoate, and t‐butyl 2‐ethylperoxyhexanoate) was tested on high‐density polyethylene (HDPE) in its molten state. The variations of the concentrations of the peroxides versus the crosslinking extent were plotted for these peroxides, and the values were compared. Dicumyl peroxide was found to be the best crosslinking agent for HDPE. The efficiency of the HDPE crosslinking with each peroxy derivative was analyzed on the basis of the behavior of the radicals generated from it. © 2004 Wiley Periodicals, Inc. J Appl Polym Sci 93: 75–81, 2004     

Peroxide crosslinking of a styrene‐free unsaturated polyester

Thermoset unsaturated polyesters are usually obtained by the crosslinking of unsaturated polyester chains dissolved in an unsaturated, reactive, monomeric diluent, which is usually styrene. This article describes a new approach in which styrene‐free unsaturated polyester chains are intrinsically cured into a crosslinked matrix. The gel time, gel content, swelling degree, glass‐transition temperature, dynamic mechanical properties, tensile properties, and molecular weight between crosslinks (calculated according to both the Flory–Rehner equation and the theory of rubber elasticity) of the crosslinked polymer are studied as a function of the peroxide concentration. All properties change considerably upon the addition of small amounts of peroxide (between 1 and 2 wt %) and change to a lesser extent with higher peroxide concentrations (up to 6 wt %). The thermal properties of the isolated gel fraction are studied as a function of the peroxide concentration. The sol fraction demonstrates a plasticizing effect on the crosslinked network, affecting the glass‐transition temperature and stress–strain behavior of the crosslinked polymer. In light of the crosslink densities derived from swelling experiments, a molecular structure and crosslinking mechanism are suggested for the gel fractions of 1 and 6 wt % peroxide crosslinked unsaturated polyester chains. © 2007 Wiley Periodicals, Inc. J Appl Polym Sci 2007     

Crosslinking of unfilled carboxylated nitrile rubber with different systems: Influence on properties

The presence of two functional groups, nitrile and carboxyl, in carboxylated nitrile rubber allows it to be crosslinked with different agents. In this study, we examined the influence of different crosslinking agents on the properties of unfilled carboxylated nitrile rubber. Significant differences were found when different crosslinking agents were used, as shown in the vulcanization curves, especially in the variation of the viscous component with the reaction time. The reaction rate was highest when organic peroxide was used, and it was lowest when metallic peroxide or copper sulfate was used. When the crosslinking agents led to the formation of ionic bonds (metallic oxide and metallic peroxide), the carboxylic groups ? COOH had a greater participation in the crosslinking. However, when copper sulfate was used, coordination bonds were formed, and the main contribution was due to the nitrile groups. Tensile strength, tear strength, and abrasion properties were superior when the crosslinking systems used led to the formation of ionic bonds. On the contrary, the compression set was optimum when covalent bonds were formed. Copper sulfate behaved as an intermediate between the two previous situations. The mechanodynamic response of the compounds also depended on the crosslinking agent used. The correlation between crosslink density by swelling in dichloromethane, maximum damping temperature by dynamic measurements, and glass‐transition temperature by differential scanning calorimetry had to be explained in terms of the crosslink type. © 2008 Wiley Periodicals, Inc. J Appl Polym Sci, 2008     

Systematic investigation on the effect of crosslinking agent type and dosage on the performance of TPU/MVQ based thermoplastic vulcanizates

Dynamic vulcanized thermoplastic polyurethane (TPU)/methyl vinyl silicone rubber (MVQ) thermoplastic vulcanizates (TPVs) were prepared in torque rheometer. The influence of the type and amount of peroxide crosslinking agent on the mechanical properties, thermal stability, micromorphology and melt flowability was systematically investigated. The results showed that the mechanical properties of the TPVs vulcanized by 2,5-dimethyl-2,5-di (tert-butyl peroxy) hexane (DBPH) first increased and then decreased with increasing the peroxide amount, while for dicumyl peroxide (DCP) vulcanizing system the mechanical properties slowly increased. Besides, the comprehensive mechanical properties vulcanized by DBPH were better than those of DCP group. The results of the thermogravimetric analysis showed that the TPVs vulcanized by DBPH had better heat stability, corresponding to the excellent thermo-oxidative aging performance and the 38% increase in tensile strength after aging. In addition, the MVQ rubber particles showed better dispersing performance for DBPH vulcanizing system. The melt flow rate of the TPVs showed a linear relationship with increasing DBPH dosage and became worse after the amount of crosslinking agent exceeded 1.5 phr. By comprehensive comparison, the TPVs have better performance when use peroxide DBPH as the crosslinking agent and the dosage is 1.5 phr.     

Effect of the vinyl concentration on the structural and rheological characteristics of peroxide‐modified high‐density polyethylenes

The effect of the hydrogenation of the terminal vinyl groups on the peroxide modification and rheological properties of high‐density polyethylene (HDPE) was investigated. The aim of the study was to determine exclusively the effect of the terminal vinyl groups on the peroxide crosslinking and rheological properties of HDPE with one polymer type. This was achieved by hydrogenation of the terminal vinyl groups of a commercial HDPE to obtain an identical material from a structural point of view, which differed only in the nature of the terminal unsaturations, and the comparison of its level of peroxide crosslinking with that of the original polymer. Hydrogenated and unhydrogenated polymer samples were modified at 170°C with different amounts of organic peroxide ranging from 125 to 5000 ppm. Changes in the molecular structure were determined by Fourier transform infrared spectroscopy, size exclusion chromatography, and rheological measurements. Hydrogenation of the terminal groups of the original polymer significantly reduced the rate of modification or crosslinking. The dynamic viscosity and elasticity increased with the level of peroxide modification. Unhydrogenated samples exhibited rapid increases in viscosity and elastic modulus, whereas their hydrogenated counterparts required about 500% of the amount of peroxide needed for the unhydrogenated sample to attain similar structural changes. © 2009 Wiley Periodicals, Inc. J Appl Polym Sci, 2010     

Thermal and wide angle X‐ray analysis of chemically and radiation‐crosslinked low and high density polyethylenes

Low and high density polyethylenes (PE) were crosslinked by two methods, namely, chemically by use of different amounts of tert‐butyl cumyl peroxide (BCUP) and by irradiation with different doses of electron beam. A comparison between the effects of these two types of crosslinking on crystalline structure, crystallinity, crystallization, and melting behaviors of PE was made by wide angle X‐ray diffraction and DSC techniques. Analysis of the DSC first heating cycle revealed that the chemically induced crosslinking, which took place at melt state, hindered the crystallization process and decreased the degree of crystallinity, as well as the size of crystals. Although the radiation‐induced crosslinking, which took place at solid state, had no significant influence on crystalline region, rather, it only increased the melting temperature to some extent. However, during DSC cooling cycle, the crystallization temperature showed a prominent decrease with increasing irradiation dose. The wide angle X‐ray scattering analysis supported these findings. The crystallinity and crystallite size of chemically crosslinked PE decreased with increasing peroxide content, whereas the irradiation‐crosslinked PE did not show any change in these parameters. As compared with HDPE, LDPE was more prone to crosslinking (more gel content) owing to the presence of tertiary carbon atoms and branching as well as owing to its being more amorphous in nature. HDPE, with its higher crystalline content, showed relatively less tendency toward crosslinking especially by way of irradiation at solid state. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 100: 3264–3271, 2006     

Crosslinking of elastomers upon ageing: a kinetic approach based on crystallinity changes followed by DSC

It was observed that crosslinking reactions resulting both from peroxide decomposition or photoageing at wavelengths longer than 300 nm involve a drastic decrease of the crystallinity of some dienic elastomers, such as polybutadienes (rich in cis 1,4 and 1,2 microstructures) and polycyclo‐octene. By comparing precisely the rate of decomposition of dicumyl peroxide and that of the crystallinity decrease, it was possible to show that the kinetics of crystallinity loss observed upon ageing can be identified with that of the crosslinking of elastomers. The results indicate that the crosslinking process can be followed directly by DSC measurement of the crystallization/melting cycle. © 2003 Society of Chemical Industry     

过氧化物交联聚乙烯热收缩管成型研究

简要介绍了聚乙烯高能辐射交联、硅烷化学交联和过氧化物化学交联,给出了交联前后分子结构变化的示意图,说明3种交联方法所得到的交联聚乙烯分子结构十分接近,在性能上基本没有差别。采用最新的过氧化物交联配方,并给出详细的生产工艺,使用最新研制的具有自主知识产权的活塞式挤出机加工成型交联聚乙烯热收缩管坯,并用自制的扩管装置扩张成型热收缩管。针对试验结果,对产品的凝胶率、力学物理性能和电性能进行了讨论,并比较了辐射交联、硅烷交联和过氧化物交联3种交联生产工艺在设备投资成本、产品质量控制、能耗、交联反应时间、产品的实际交联度和产品的表面质量等方面的优劣。     

Monitoring polyolefin modification along the axis of a twin screw extruder. I. Effect of peroxide concentration

The evolution of the structure of polyolefins with different ethene/propene ratios in the absence or in presence of peroxide was monitored along a twin screw extruder. Small samples were quickly collected from the melt at specific barrel locations and characterized by rheological measurements. The rheological properties of the polyolefins are hardly affected when processing is carried out in the absence of peroxide. In the presence of peroxide both branching/crosslinking and degradation occur along the extruder, until the peroxide is fully converted. The degree of branching/crosslinking and/or degradation depends on the ethene/propene ratio, on the original molecular weight of the polymer and on the amount of peroxide added. © 2001 John Wiley & Sons, Inc. J Appl Polym Sci 81: 58–68, 2001     

Effect of molecular structure and topology on network formation in peroxide crosslinked polyethylene

The present study compared the crosslinking performance of single site linear low density polyethylenes (LLDPE) with high pressure, free radical polymerised, low density polyethylenes (LDPE). The difference in crosslinking performance is not fully explained by different structural parameters such as molar mass distribution (MMD), M_n, MFR₂ value and vinyl groups but is related more to the phenomenon of a long chain branched LDPE macromolecule being smaller in size in the molten state than a macromolecule of a linear LLDPE sample of the same molar mass. The result of the difference in size is that the LDPE will contain a larger number of intramolecular crosslinking points than the LLDPE, which, on the other hand, will contain a larger fraction of intermolecular crosslinking points. The crosslinking points mentioned are of either a physical or chemical nature. From the perspective of the network build-up, the intermolecular crosslinking points are the most efficient. To compensate for the larger fraction of intramolecular crosslinking points in LDPE, more peroxide can be added or vinyl groups can be introduced.     

Crosslinked poly(ethylene oxide) hydrogels

Poly(ethylene oxide) with a molecular weight of 2,000,000 was crosslinked by a difunctional peroxide in the molten state. We determined the molecular weight between crosslinks by swelling the samples with deionized water and by indentation and dynamic mechanical analysis. Results were compared with the calculated optimum molecular weight between crosslinks. Fair agreement was obtained between the experimental methods. However, the efficiency of peroxide‐induced crosslinking was very low. © 2003 Wiley Periodicals, Inc. J Appl Polym Sci 88: 1451–1455, 2003     

SEBS化学交联的热分析动力学研究

采用非等温差示扫描量热(DSC)分析法,在交联剂过氧化二苯甲酰(BPO)存在下,对部分氢化的苯乙烯-丁二烯-苯乙烯三嵌段共聚物(SEBS)的化学交联过程进行了热分析动力学研究,在不同升温速率下获得SEBS交联反应的DSC升温曲线,采用Model-free (无模型) 分析法包括Friedman、Ozawa-Flynn-Wall和Kissinger等三种方法分别对SEBS交联反应进行了热动力学分析,求出其动力学初始参数值,然后用Model-fitting (模型拟合)分析法通过选择动力学模型,采用多元非线性回归优化得到了精确的模型参数。所得动力学模型表明BPO引发的SEBS交联过程经过了三步反应,每步反应的活化能依次减少。此优化的动力学模型可用来预测不同温度下反应时间和交联度之间的关系,表明可通过控制交联温度和反应时间得到所需交联程度的SEBS产品,从而达到其性能设计的目的。