In situ fibrillation of isotactic polypropylene in ethylene-vinyl acetate: Toward enhanced rheological and mechanical properties

In situ microfibrillar reinforced composites with ethylene-vinyl acetate (EVA) as matrix and isotactic polypropylene (iPP) as dispersed fibrils were successfully fabricated by multistage stretching extrusion with an assembly of laminating-multiplying elements (LMEs). Four types of EVA with different apparent viscosity were utilized to study the influence of viscosity ratio on the morphology and mechanical properties of EVA/iPP in situ microfibrillar blends. The scanning electron micrographs revealed that the dividing–multiplying processes in LMEs could effectively transform the morphology of iPP phase into microfibrils and the morphology of iPP microfibrils strongly depended on the viscosity ratio. Higher viscosity ratio was favorable for formation of finer microfibrils with narrower diameter distribution. The morphology development of iPP with different viscosity ratio greatly affected the rheological and mechanical properties of EVA/iPP blends. The dynamic rheological results shown that the iPP microfibrils were helpful to increase the storage modulus and loss modulus. The tensile test indicated that the mechanical properties of EVA/iPP blends were controlled by the morphology of iPP phase and the polarity of EVA matrix. © 2019 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2019 , 136, 47557.     

Effect of vinyl acetate content on the photovoltaic-encapsulation performance of ethylene vinyl acetate under accelerated ultra-violet aging

The vinyl acetate (VA) content in ethylene vinyl acetate (EVA) can significantly affect its performance as an encapsulant in photovoltaic modules under field conditions. EVA films of varying VA content (18, 24, 33, and 40%) have been prepared using twin screw extruder with the necessary additives and subsequently cured at 150 °C. All the EVA films have been subjected to UV radiation at a wavelength of 340 nm for 1000 and 2000 h to simulate accelerated field aging. The effects of accelerated aging on the gel content, mechanical properties, transmittance, Fourier transform infra-red (FTIR) spectra, thermal stability, degree of crystallinity, and yellowness have been studied. The observations made in this study of UV aging up to 2000 h suggests that the optimum range of VA content in EVA should be between 18 and 33% by weight. VA content beyond 40% degrades almost all properties needed for an encapsulate material after aging of only 2000 h. VA content of around 18% is the most stable under UV aging conditions but has a slightly lower value of transmittance for the unaged sample although the difference in transmittance between different specimens decreases with UV aging. © 2019 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2020 , 137, 48268.     

高反光率EVA胶膜的制备与性能研究

文章介绍了高反光率EVA胶膜的制备过程,并将其与常规EVA胶膜以及双玻组件用EVA胶膜进行封装组件功率及黄色指数变化效果对比分析。研究结果表明:采用高反射功能助剂改性方法制备的高反光率EVA胶膜,具有优异抗紫外辐射老化能力,同时能够提高组件的光电转换效率及功率。     

PVC树脂的共混改性

分析了PVC共混改性的基本原理及特点,介绍了ABS、MBS、CPE、ACR、EVA等PVC树脂共混改性剂的主要牌号、改性效果及应用范围。     

EVA和BSC的比较与分析研究

文章介绍了EVA和BSC两种业绩评价方法,通过对其相关概念的引入、EVA和BSC各自适合的企业以及整合的相关性、可行性的分析。     

Composites of ethylene‐vinyl acetate copolymers with modified magnesium hydroxide–thermo‐oxidative ageing

Flame retardant composites must perform their protective roles permanently, also under conditions of intermittent or long‐term exposure to sunlight, moisture or increased temperature. The aim of our work was characterization of the thermo‐oxidative ageing (90 °C) and the changes in flammability of ethylene‐vinyl acetate copolymer composites with 40 and 60 wt.% of magnesium hydroxide. The neat polymer and its composites were investigated for their thermal (DSC) and structural (FTIR) characteristics as well as their density, melt flow index, tensile properties and combustibility during ageing test. As FTIR results identified the different carbonyl groups in copolymer were created, the highest oxidation intensity was observed for neat copolymer. That process was accompanied by the scission of the polymer macromolecules, especially for first 700 h of thermal ageing. Thermo‐oxidative ageing resulted also in the reduction of flammability of the test materials. The highest reduction was observed for neat polymer. The changes in some properties as analysed both for the copolymer and for its composites after over 700 h of ageing were indicative for initiation of cross‐linking of copolymer molecules after that time. Copyright © 2014 John Wiley & Sons, Ltd.     

Pickering Emulsion Polymerization of Styrene using Nano-SiO2 and Subsequent Use of the Produced Core–Shell Structures as Fillers for Ethylene Vinyl Acetate Copolymer and Polypropylene

Solid particles can stabilize emulsions instead of conventional surfactants. Emulsion polymerization of styrene, as an example of polymerizable oil, was processed in the present work after ultrasonication of styrene in water in the presence of silica nanoparticles as stabilizer. Field emission scanning electron microscopy, equipped with energy-dispersive X-ray unit, and transmission electron microscopy confirmed the formation of polystyrene particles covered by a sheath of self-assembled silica. Addition of these hybrids in different loadings (2–14 wt%) to polypropylene and ethylene vinyl acetate copolymer could improve their tensile strength and hardness. The mechanical enrichment could be attributed to the action of the silica shell layer to delay the phase separation process encountered between the polystyrene from one side and polypropylene/ethylene vinyl acetate from other side, which translates into different extents of reinforcements.     

Grafting maleic anhydride onto EVA and effect on the physical and rheological properties of PETG/EVA-g-MAH blends

Maleic anhydride (MAH) was grafted onto ethylene vinyl acetate copolymer (EVA) in the internal mixer in the presence of dicumyl peroxide (DCP), and a prepared reactive compatibilizer, MAH-g-EVA, was blended with Poly (ethylene glycol-co-cyclohexane-1,4-dimethanol terephthalate) (PETG). The gel content determination and element analysis (EA) was performed to confirm the grafting reaction. It was found that grafting reaction of MAH on to EVA could compete with crosslinking reaction of DCP during the modification process. In addition, the introduction of small amount of MAH showed a great effect on reducing gel content by decreasing crosslink reaction. As MAH content increased, grafted MAH concentration increased, whereas the grafting yield decreased. It was also confirmed that MAH-g-EVA acted as a reactive compatibilizer in the blend with PETG, and enhanced compatibility by reacting with the hydroxyl end groups, OH, of PETG. Addition of EVA in the blend leads a plastic deformation of PETG, and MAH had a great effect on enhancing interfacial adhesion resulting in significant increasing of % strain; however, improved compatibility could not be changed much in low strain tensile strength and Young's modulus. © 2012 Wiley Periodicals, Inc. J Appl Polym Sci, 2012     

THE EFFECT OF TEMPERATURE ON CONTROLLED RELEASE OF HEPARIN FROM POLYURETHANE AND ETHYLENE VINYL ACETATE COPOLYMER

The objectives of this study were to examine the effect of elevated temperatures on the release kinetics of heparin from polyurethane (PU) and ethylene vinyl acetate copolymer (EVA), and on the biological activity of heparin released from the polymer matrix. Monolithic samples, prepared by dispersing heparin in solutions of PU and EVA, were fabricated and evaluated for in vitro release rates. Comparisons were made on the release rate of heated and non-heated samples. Heating at 120°C had little effect on the release kinetics from PU and an increase on release from EVA. Bioactivity of pure heparin and heparin released from PU was also evaluated and were found to remain stable up to 210°C.     

有机硅和EVA对阻燃聚乙烯体系的影响

为提高碳酸镁/氢氧化铝复配阻燃聚乙烯体系的性能,将有机硅和EVA添加到阻燃体系中,测量其氧指数、拉伸强度和断裂伸长率。实验表明:有机硅是该体系很好的阻燃协效剂,而用EVA改性基础树脂,不但可以提高体系的阻燃性能,还可以提高体系的断裂伸长率。