紫外光辐照聚乙烯膜接枝丙烯酸的研究

以低密度聚乙烯膜为接枝基材，丙烯酸为接枝单体，考察了紫外光辐照聚乙烯膜接接反应的主要影响因素，以及接权后聚乙烯膜的力学性能变化。     

不同抗预交联剂对硅烷接枝聚乙烯稳定性的影响

以线性低密度聚乙烯LL6101与218W为基体,将不饱和硅烷接枝到线性低密度聚乙烯分子链上,并通过加入苯乙烯及已内酰胺来考察两种抗预交联剂对不饱和硅烷接枝线性低密度聚乙烯的影响。通过红外光谱推测了以上两种抗预交联剂参与反应的机理,利用动态频率扫描研究了不同配方体系的流变行为,实验结果表明,两种抗预交联剂均有一定的阻聚作用,其中聚苯乙烯的效果更明显。根据对各体系的反应机理讨论可知,苯乙烯中的共轭作用对硅烷接枝聚乙烯稳定性的影响更明显。对各体系的流变测试结果也验证了以上结论。     

聚乙烯的环境应力开裂

本文评论了聚乙烯(PE)的环境应力开裂(ESC)的有关问题。在这个问题上近十年来最重要的成就在于把断裂力学成功地用于分析ESC机理。已经有了许多改进PE耐环境应力开裂性(ESCR)的方法,但大多数尚属经验性方法。     

碳黑/接枝聚乙烯导电复合材料的研究

利用Co^60-γ射线共辐照法在聚乙烯分子上接枝极性基因。以改性的聚乙烯为基体，碳黑为导电颗粒，制备碳黑／接枝聚乙烯导电复合材料。用多用电表对导电复合材料电性能进行了测试。结果表明：接枝改性后的聚乙烯作为导电复合材料的树脂基体，可改善导电复合材料的电阻稳定性，提高导电复合材料的升阻比。     

LDPE固相接枝MAH及其产物在PA66/LDPE共混物中的应用

采用固相接枝法制备低密度聚乙烯(LDPE)接枝马来酸酐(MAH),并利用FT-IR表征了接枝产物的化学结构.研究了反应温度、引发剂用量、单体用量、界面剂用量以及反应时间对产物接枝率和交联度的影响.同时考察了接枝产物(LDPE-g-MAH)对聚酰胺66/低密度聚乙烯(PA66/LDPE)共混物的力学性能和形态的影响.结果...     

共单体促进聚乙烯熔融接枝硅氧烷的研究

以低密度聚乙烯和线性低密度聚乙烯为基体，研究了两种共轭效应大于3-(甲基丙烯酰氧基)丙基三甲氧基硅氧烷(KH570)、极性效应与KH570差值较大的共单体N-苯基马来酰亚胺(N-PMI)和甲基丙烯酸-2-羟基丙酯(2-HPMA)的加入对聚乙烯(PE)接枝硅氧烷KH570的影响。利用红外光谱分析证实了PE已经成功接枝了硅氧烷KH570和共单体，熔体流动速率、接枝率、凝胶率测试结果表明，两种共单体的加入，均能提高PE接枝硅氧烷的效果，而且N-PMI促进接枝的效果明显优于2-HPMA。当KH570用量为0.84g,共单体N-PMI和2-HPMA用量分别为0.84g和1.26g时，产物接枝率达到最大，分别为1.23%和0.85%。     

反应性挤出聚乙烯接枝马来酸二丁酯的研究

将过氧化二异丙苯容入马来酸二丁酯，再与低密度聚乙烯粒料混合均匀，在单螺杆挤出机中进行反应性挤出，可得到聚乙烯接枝马来酸二丁酯产品（ＰＥ－ＤＢＭ）。产品经二甲苯溶解，丙酮沉淀纯化数次后，由化学分析和红外鉴定表明，在挤出反应中确有４０％以上的ＤＢＭ单体接枝到聚乙烯链上，接枝率可达到０．３ＤＢＭ／１００Ｅ。ＤＳＣ研究静态熔融反应表明，反应只有在１５０℃才开始反应，１７５℃达到峰值，１９０℃全部反应终止。     

两步法LDPE/HSS表面光接枝的研究

采用两步表面光接枝方法研究了乙烯基苯磺酸(HSS)在低密度聚乙烯(LDPE)膜表面的接枝聚合,使LDPE膜表面有效强酸化．探讨了各反应条件对表面接枝的影响规律,利用称量法、表面水接触角测定法、红外光谱分析、扫描电镜观察等手段对表面接枝膜进行了表征。     

聚硅氧烷接枝乙烯基咔唑、十一烯酸乙酯聚合物的荧光光谱

研究了聚硅氧烷接枝乙烯基咔唑聚合物的氯仿稀溶液的荧光光谱，它在３７０ ｎｍ 处的单生色基团荧光峰的强度随溶液浓度的增加而减弱，当其生色基团的浓度为１．１９３×１０－ ３ ｍ ｏｌ／Ｌ时，除单生色基团荧光峰外，还出现由分子内相邻生色基团生成的激基缔合物峰；而在其固体的荧光光谱中仅出现一很强的激基缔合物荧光峰。顺丁烯二酸酐是聚硅氧烷接枝乙烯基咔唑聚合物稀溶液的有效淬灭剂，其淬灭规律符合Ｓｔｅｒｎ－Ｖｏｌｍ ｅｒ方程。接枝单体乙烯基咔唑、十一烯酸乙酯的摩尔配比为８∶２ 及５∶５ 的聚硅氧烷接枝共聚物的稀溶液荧光光谱中均呈现一单生色基团荧光峰，而它们的固体薄膜的荧光光谱中仅出现一很强的激基缔合物荧光峰，在该类无规接枝共聚物的固体中，激基缔合物可在分子内不相邻生色基团间及分子间、生色基团间生成。     

硅烷接枝交联聚乙烯的研究

用不同结构的乙烯基硅烷与聚乙烯进行熔融接枝及水解缩合交联反应，通过对 支物的结构表征，交联行为以及交联前后结晶性质，高温应力－应变曲线的测定，研究了不同结构的乙烯基硅烷对硅与聚乙烯的接枝反应和交联反应的影响。     

Environmental dynamic fatigue crack propagation in high density polyethylene: an empirical modelling approach

Part of a programme to study environmental dynamic fatigue crack propagation in engineering thermoplastics is presented. High density polyethylene has been studied in terms of its stress cracking properties under dynamic loading conditions in detergent. This work complements previous investigations on stress cracking in detergent under static loading. The stress cracking was found to vary according to loading conditions and in conclusion, a dependence of crack growth rate on test frequency, amplitude and level of stress intensity factor is reported. An emperical model describing environmental fatigue crack propagation is proposed which adequately represents the experimental results of high density polyethylene, Nylon 66 and which, it is suggested, may be suitable for use with other polymers.     

Environmental stress cracking of polyethylene high density (PE‐HD) induced by liquid media – Validation and verification of the full‐notch creep test (FNCT)

The full‐notch creep test (FNCT) is widely used to characterize the slow crack growth (SCG) behavior of polyolefin materials in “inert” media as well as effects of environmental stress cracking (ESC) in which the medium has decisive influence on damage mechanism and time to failure. The test is of greatest importance for pipe and blow molding types of polyethylene, high density (PE‐HD). Usually the full‐notch creep test is applied as a standardized testing method (ISO 16770) using a few universal liquid media, such as solutions of Arkopal N 100. In our study, selected relevant polyethylene, high density materials are investigated also in real media – practical formulations as well as representative pure chemicals – and influences of temperature and geometry of specimen and notch are explicitly addressed. Furthermore, the investigations comprise also the environmental stress cracking behavior of polyethylene, high density in media that are sorbed to a significant extent – examples are diesel and biodiesel – based on comparison with samples previously saturated with those media. Thus, also the underlying diffusion controlled sorption process has to be assessed before. The investigations were performed using a full‐notch creep testing device with 12 individual sub‐stations, each equipped with individual electronic stress and temperature control and continuous online monitoring of the specimen elongation.     

微交联聚乙烯应力-光氧老化开裂行为的研究

为了提高桥梁缆索护套耐老化性能,通过制备微交联的聚乙烯材料研究不同交联度聚乙烯材料的应力-光氧老化开裂行为.采用剥离一段缆索护套并测定收缩率来计算聚乙烯护套在实际中的内应力,利用表面形貌观察、形变量测定、红外光谱分析、差式量热扫描法、凝胶含量测定等表征手段研究样品老化过程中的老化开裂行为.研究表明：随着交联度的增加,聚乙烯材料发生断裂的时间先增加后减少,表面裂纹发展的速度先增加后减小,裂纹发展速度及抗老化开裂性能最佳的交联度约为10%;聚乙烯材料的氧化速率与断裂时间呈正相关;表面裂纹出现后,材料被完全氧化;老化过程中,聚乙烯凝胶含量和结晶度均不断上升.     

某型包装箱的低密度聚乙烯缓冲结构设计与分析

目的 基于低密度聚乙烯材料设计一种包装箱的缓冲结构,以满足冲击加速度的设计要求。方法 采用低密度聚乙烯材料对应的最大加速度-静应力曲线进行理论计算,设计出包装箱缓冲结构的初始模型,运用Ansys Workbench有限元仿真软件对包装箱整体进行水平跌落仿真,并对仿真结果进行分析。结果 当缓冲垫设计厚度为75 mm时,包装箱整体跌落后受到的最大冲击加速度低于40g,满足设计要求。结论 基于低密度聚乙烯材料设计的缓冲结构能够对包装箱提供有效的缓冲防护,缓冲性能满足要求。     

Multiple film cracking in film/substrate systems with residual stresses and unidirectional loading

Multiple film cracking in film/substrate systems is analyzed in the present study. Specifically, the experimental measurements of multiple cracking of SiO _x films of various thicknesses on polyethylene terephthalate substrates are analyzed. The system is subjected to both residual stresses and unidirectional tensile loading. Considering a three- dimensional geometry, an analytical model is developed to derive the stress distribution in the system, and the film-cracking problem is analyzed using both the strength and the energy criteria. Compared to the strength criterion, the energy criterion shows better agreement with the measurements of the crack density versus applied strain relation.     

Spannungsrißbildung und Spannungsrißkorrosion bei Kunststoffen

Environmental stress cracking and stress-corrosion cracking in plastics Plastics are being used to an increasing extent in fields which have hitherto been the reserve of other, usually metallic, materials. Owing to their good processability and chemical resistance, plastics engineering materials are for example employed for vessels, pipes, valves and fittings, blowers, pumps and gear wheels. In these applications they are not only exposed to liquid media but, are also subjected to occasional or continuous mechanical stress. The trouble is that there are media to which plastics in the stress-free state are absolutely immune, but that, when tensile stresses are present, cracking may occur; this phenomenon is called environmental stress cracking. It is therefore necessary for the design engineer both to know whether the medium to be handled causes environmental stress cracking, and to be familiar with the other properties of the material. The following article describes the most important methods of detecting environmental stress cracking and the most important media which cause this form of cracking in common plastics materials.     

Fracture behaviour and its relation to critical current of silver-sheathed Ba2YCu3O7-x superconducting composite wires and tapes

Silver-sheathed Ba₂YCu₃O_7-x superconducting composite wires and tapes were prepared by rolling, drawing, swaging and pressing methods. The fracture behaviour and its influence on critical current at O T at 77 K of the Ba₂YCu₃O_7-x were investigated. The oxide was found to show multiple fracture under applied tensile stress, and the critical current density and tensile strength of the oxide in the rolled, swaged and pressed samples were higher than those in the drawn samples. When the working amount was high, the current density and the strength of the oxide were found to become high. Within the present conditions, there was a correlation between critical current density and cracking stress: the higher the cracking stress, the higher the critical current density became. The cracking stress of the present oxide was determined to be 50MPa at most, being far lower than that of the Nb₃Sn compound (800 to 2000 MPa). The critical current density of the rolled, swaged and pressed samples was reduced rapidly when exerted stress on the oxide exceeded the cracking stress, while the reduction in the drawn samples occurred gradually. A strong dependence of the critical current, as a function of applied stress and cracking stress of the oxide, on the measured portion due to scatter in the size of defects contained in the oxide, was found.     

Synthesis of multi-walled carbon nanotubes via pyrolysis of plastic waste using a two-stage process

The pyrolysis of different plastic waste types such as low density polyethylene (LDPE), high density polyethylene (HDPE), polypropylene (PP), polyethylene terephthalate (PET) and polystyrene (PS) for producing multi-walled carbon nanotubes (MWCNTs) using a two-stage process has been investigated. Firstly, the cracking of plastic wastes was carried out at a temperature of 700°C to produce hydrocarbon gases. In the second stage, the produced hydrocarbon gases were decomposed at 650°C on the surface of the Ni-Mo/Al₂O₃ catalyst to form CNTs. Various analytical tools such as XRD, TPR, TGA, Raman spectroscopy and TEM were used to describe both the fresh catalyst and the obtained CNTs. The results showed that the amount of the hydrocarbon gases was related to the type of plastic waste and hence the CNT yield. Accordingly, LDPE or PP was decomposed to produce the largest gases yield of 72.5 or 70.7 wt%, respectively. As a result, a large CNTs yield of 5.8 and 5 g/g_cat can be achieved by pyrolysis of PP and LDPE waste, respectively. However, a small yield of CNTs with little quality and low purity was obtained by using PS or PET waste as the carbon feedstock.     

Toughening of polyester resins through blending with polyolefins

The effect of blending low concentrations (1 to 10%) of polyolefins on the crystallization and irreversible deformation behaviour of polyester (PET) resins was investigated. The olefin particles did not nucleate crystallization of PET from the melt but did depress the rate of crystallization. Decreases in the cold crystallization temperature of PET during heating from the glassy state in blends with linear low density polyethylene (LLDPE) and high density polyethylene (HDPE) were attributed to stress induced crystallization created by large volume expansions associated with melting of the olefin particles. A sharp transition in fracture strain for PET and the PET-olefin blends was observed with strain rate, where at low strain rates fracture occurred during work hardening, and as the strain rate increased, fracture occurred during cold drawing. The transition corresponded with a decrease in draw stress, a decrease in draw ratio and an increase in density of the neck. A shift in the transition to higher strain rates for the blend compositions was attributed to increased rates of crystallization and orientation due to strain induced crystallization at the stress fields surrounding the olefin particles. As the strain rate increased and the cold drawing process became more adiabatic, the mechanical behaviour was controlled by the kinetics of crystallization and orientation.     

The ESC behaviour of a toughened PMMA after exposure to gamma radiation

This work is a sequence of a previous one where we investigated the influence of gamma radiation dose on environmental stress cracking (ESC) of a conventional poly(methyl methacrylate) (PMMA) (Sousa et al. Polym Degrad Stab 92:1465, 2007). In that work, we observed that low doses of gamma radiation intensified the ESC effects, but on higher doses the gamma radiation effect was predominant over the stress cracking. The present work describes a similar study, but using a toughened PMMA (t-PMMA). The polymer was submitted to gamma radiation doses up to 100 kGy, and then tested to ESC susceptibility through tensile and relaxation tests. Two different types of active fluids were used: ethanol (an aggressive one) and ethylene glycol (a moderate liquid stress cracking agent), based on absorption results. A synergistic effect between ESC and radiation degradation was noted, with a substantial decay in mechanical properties when these two effects were present. The ethanol action caused dendritic pattern formation in the fracture surfaces of t-PMMA, as revealed by scanning electron microscopy.