Beurteilung von lichtschutzsystemen bei polyolefinen in der natürlichen und künstlichen bewitterung

Vestolen A 6016 and Vestolen P 5200 were acceleratedly weathered in a Xenotext 1200 and a Xenotest 450. By variation of operating conditions of Xenotest 1200 different spectral distributions in the UV region (with and without UV filter) were obtained. In Xenotest 450 polyethylene and polypropylene showed approximately the same process of damage, wheras polyethylene and polypropylene showed clear different “spectral sensitivities” in Xenotest 1200. The maximum of UV capacity which is possible in Xenotest 1200 enables a maximum of time accelerating effect - also when light protecting systems are used - but it does not admit a more exact evaluation of the quality of a light protecting formulation. The test of light protecting formulations based on UV absorber, HALS and combinations thereof showed, that evaluation can be very different and does not always conform with the results of out door weathering.     

气相法mPE的性能剖析

茂金属聚乙烯（mPE)具有优越的力学性能和光学性能，这与茂金属催化剂的催化性能及其聚合物特殊的链结构形式密切相关。对国内开发的mPE进行了结构表征，结果表明：mPE薄膜的力学性能和光学性能明显优于线型低密度聚乙烯产品，其耐穿刺性能明显好于其他聚乙烯产品。     

Structure–property relationships of composite films

Coextruded multifilms of varying chemical composition and structure were studied by the dynamic mechanical technique. The films studied were two- and three-ply combinations of a polyimide (Kapton) and fluorinated ethylene–propylene copolymer (FEP) and four other two-ply polyethylene and modified polyethylene composites: low-density polyethylene (LDPE)–ionomer, rubber-modified high-density polyethylene (HDPE)–ionomer; ethylene–vinyl acetate (EVA) copolymer–LDPE, and EVA-modified HDPE–LDPE. The mechanical spectra of individual film components were also obtained at 110 Hz between ?120° and 120°C (220°C for the Kapton–FEP system). Mechanical relaxations were examined to determine the degree of interaction between adjacent films and correlate them with tensile and ultimate properties of the composite.     

Graft copolymer modification of polyethylene–polystyrene blends. II. Properties of modified blends

The use of graft copolymers of styrene onto polyethylene as additives to improve the mechanical properties of polyethylene–polystyrene blends is described. Blends containing equal proportions of low-density polyethylene and polystyrene were selected for this study since this composition represents the poorest balance of properties in this system. Graft addition generally increased both the yield strength and the elongation at break of the blend. Of the grafts employed, those prepared at an irradiation dose near 0.5 megarad appear optimal for this purpose. These conditions apparently balance the beneficial effects of grafting extent and the detrimental effects of crosslinking, both of which increase with irradiation dose.     

Rheology modifier additive for enhanced processability of polyethylene for blown-Film applications

Polyethylene is a versatile polymer suitable for a large variety of flexible and rigid packaging applications. Its mechanical and rheological properties can be tuned across a wide range by controlling its molecular architecture, such as the amount and distribution of olefinic comonomers (short chain branching), long chain branching, and molecular weight distribution. Linear low-density polyethylene (LLDPE) is known for its high toughness which enables downgauged film structures and low-density polyethylene (LDPE) is known for its excellent shear thinning and melt strength which enables enhanced processability and high throughput, such as on blown film lines. In order to obtain a balance of toughness and processability on films produced on blown film lines, blends of LLDPE and LDPE are commonly used. In this paper, we describe additive-based approaches, including a new product, DOWLEX™ (TM = trademark of the Dow Chemical Company (“Dow”) or an affiliated company of Dow) GM AX01, which enhances melt strength and other rheological properties of polyethylene, enabling fabrication of films with lower LDPE content while still maintaining excellent rheological properties and higher toughness versus conventional LLDPE/LDPE blends. The higher toughness enables downgauging without loss of mechanical properties, which in turn reduces consumption of polymer resulting in a more sustainable solution.     

高开口型线形低密度聚乙烯的性能研究

研究了高开口型线形低密度聚乙烯（PE-LLD）DFDA7042H的物理性能、相对分子质量、支化度和流变性能,并对其生产的薄膜产品的性能进行了测试,且与市场认可的进口产品进行了对比。结果表明,与进口产品相比,工业化生产的DFDA7042H物理性能大致相同,相对分子质量稍高,相对分子质量分布较宽;DFDA7042H的剪切应力和剪切黏度更低,适合在较低的温度下加工;DFDA7042H吹制的薄膜的动摩擦因数与进口产品接近,开口性较好;同时薄膜的雾度较低,具有更高的透明性,其他性能与进口产品接近,能够满足高速包装膜使用要求。     

增容剂LDPE-g-MAH对木质素/聚乙烯吹塑薄膜形貌与性能的影响

研究了低密度聚乙烯与马来酸酐的接枝共聚物LDPE-g-MAH对木质素/低密度聚乙烯共混体系热性能、红外光谱分析力学性能、流变行为以及微观形态的影响.DSC-TG综合热分析表明添加增容剂的共混物的熔融温度降低,热稳定性提高;红外光谱分析表明木质素与LDPE-g-MAH之间存在分子间氢键相互作用,流变性能分析表明共混物体系具有可加工性;扫描电子显微镜（SEM）照片显示添加增容剂后分散相尺寸明显减小,分散程度提高;PE-g-MAH有效提高了木质素/聚乙烯吹塑薄膜的力学性能,且当木质素、聚乙烯和LDPE-g-MAH质量比为25/75/10时,力学性能最优.     

Graft copolymer modification of polyethylene–polystyrene blends. I. Graft preparation and characterization

The preparation and characterization of styrene–low-density polyethylene graft copolymers for addition to blends of polyethylene and polystyrene to improve blend mechanical properties is described. The direct method of grafting with ⁶⁰Co radiation was employed using the polyethylene in pellet form. This approach gave good grafting efficiency with maximum yields limited to about 1 g of styrene reacted per gram of polyethylene. Excessive crosslinking at radiation doses beyond about 1 mrad was detrimental to the melt processibility of the graft. Crystallinity, dynamic mechanical properties, morphology, and stress–strain behavior of the grafts were examined and compared with melt blends of similar composition in order to better characterize the material produced.     

The preparation and tensile properties of polyethylene composites

Single polymer composites have been prepared using different morphologies of polyethylene as matrix and as the reinforcement. Depending on annealing conditions, the ultraoriented fibers used as reinforcement can have higher melting points (ca. 139°C) than the matrix made from the same conventionally crystallized high-density polyethylene (ca. 132°C) or from low-density polyethylene (ca. 110°C). The optimum temperature has been assessed for bonding to occur by growth of transcrystalline regions from the melt matrix without considerable modulus reduction of the annealed ultraoriented and reinforcement fiber or film. Pullout tests have been used for determining the interfacial shear strength of these single polymer composites. The interfacial shear strength for the high-density polyethylene films embedded in a low-density polyethylene matrix is 7.5 MPa and for high-density polyethylene self-composites is 17 MPa. These values are greater than the strength for glass-reinforced resins. The strength is mainly due to the unique epitaxial bonding which gives greater adhesion than the compressive and radial stresses arising from the differential shrinkage of matrix and reinforcement. The tensile modulus of composites prepared from uniaxial and continuous high-density polyethylene films embedded in low-density polyethylene obeys the simple law of mixtures and the reinforced low-density polyethylene modulus is increased by a factor of 10. High strength cross-ply high-density-polyethylene—low-density-polyethylene laminates have also been prepared and the mechanical properties have been studied as the film orientation is varied with respect to the tensile axis.     

加速紫外老化对聚乙烯薄膜力学性能的影响

介绍了聚乙烯(PE)薄膜老化机理,并对PE薄膜进行了人工加速紫外光老化试验。分析了老化时间对PE薄膜力学性能的影响。结果表明:紫外光的照射使PE的化学键发生交联和断裂反应,其中断裂反应占主导,使聚合物分子量减小,物理性能下降;PE薄膜的拉伸强度、断裂伸长率和弹性模量随老化时间的延长而降低;PE薄膜抵抗破坏的能力在老化60 h以上会急剧下降,而此时弹性模量的变化趋势变得平缓,断裂伸长率与老化时间近似成线性关系递减。     

Surface modification of polyethylene by photochemical grafting with 2-hydroxyethylmethacrylate

The photochemical grafting of 2-hydroxyethylmethacrylate onto low-density polyethylene film is described. The grafting technique employed involved irradiating a solution of 2-hydroxyethylmethacrylate and benzophenone in acetone spread between films of poly(ethylene terephthalate) or glass and low-density polyethylene. After irradiation for 2 min, the contact angle of the polyethylene films with water fell from 97° to about 50°. The contact angle of the poly(ethylene terephthalate) substrate also fell during grafting. X-ray photoelectron spectroscopy was consistent with the presence of poly(2-hydroxethylmethacrylate) at the surface of the polyethylene. The effect of solvent on the photochemical grafting of 2-hydroxyethylmethacrylate onto low-density polyethylene is discussed. © 1993 John Wiley & Sons, Inc.     

Photo-Oxidation and photo-stabilization of blends of low-density polyethylene and styrene-butadiene-styrene copolymers

The photo-oxidation of blends of low-density polyethylene and styrene-butadiene-styrene block copolymers has, been shown to result mainly from the degradation of the pollybutadiene part of the material. The solution infra-red and fluorescence spectra, and mechanical properties have been studied as a function of the irradiation time. Evidence of some interaction between the components of the blend could be obtained.     

纤维素内塑化材料的制备及性能

用微波辐射法快速合成了纤维素长链脂肪酸酯。通过对改性产物的红外光谱及核磁共振光谱表征,证明柔性脂肪酸酯基引入了纤维素骨架。对溶液浇铸法所得薄膜材料的耐水性、玻璃化温度(Tg)、热稳定性、拉伸强度及断裂伸长率进行了分析测定,探讨了取代度对材料性能的影响。结果表明,改性材料表面具有良好的疏水性质,其接触角均在90°左右;由于柔性酯基链的引入,所制备的纤维素改性薄膜具有一定的内塑化性能。取代度为1.8的样品,其Tg为153℃,起始分解温度为198℃,断裂伸长率为50%,拉伸强度约为12 MPa,与线性低密度聚乙烯相当。     

Dynamic mechanical properties of binary blends of different polyethylenes. I. Nonisothermal treatment

The relaxation processes and thermal properties of a series of blends of a highly linear high-density polyethylene (HDPE) with several branched high-density, linear low-density (LLDPE) and low-density polyethylenes (LDPE) have been measured. For the sake of comparison, all the samples were subjected to the same thermal treatment, that is, a rapid quenching from the molten state. The mechanical properties have been analyzed, taking into consideration the crystallization behavior of each sample. The existance of cocrystallization provides a bigger change in the dynamic mechanical properties than when segregation takes place. The observed changes in the end-corrected storage modulus supports this conclusion as well as those associated with the α, β, and γ relaxation temperatures.     

氧化铝对聚乙烯防雾滴薄膜性能的影响

以氧化铝作为减缓剂加入聚乙烯(PE)防雾滴薄膜中,通过对薄膜微观观察,发现氧化铝在PE中具有较好的分散性,与PE界面结合性能好.通过对PE防雾滴薄膜光学性能、力学性能及流滴性能等测试发现,当氧化铝含量为6％时,PE薄膜光学性能及力学性能最好,雾度达到10.8％,透光率达到92.3％,纵向拉伸强度达到25.3 MPa,断...     

The effect of sand wind,temperature and exposure time on tri-layer polyethylene film used as greenhouse roof

This work aims at studying the degradable effect of artificial ageing on tri-layer stabilised low-density polyethylene (PE) films used as greenhouse cover in the North Africa environment. The film was supplied by Agrofilm company, Algeria. Colour additives and infra-red and ultraviolet stabilisers were used. Optical, thermal, surface and mechanical properties have been investigated for virgin sample and samples exposed to sand wind for different exposure periods (1, 2, 4 and 8?h) of artificial ageing at a temperature of 40°C simulating Saharan environment. The findings of this study show that the harsh environmental conditions of exposure to temperature and sand wind have significant degradable effects on the properties of the PE film. The transmission of the film and its mechanical properties have reduced significantly due to exposure to sand wind and temperature. The study revealed also that the degradation parameters measured are directly related to the criteria for evaluating the effectiveness of agricultural greenhouse.     

An electromagnetic dynamic film blowing technology for mLLDPE

Metallocene linear low‐density polyethylene (mLLDPE) has superior physical and mechanical properties. However, mLLDPE has very poor film blowing processibility. To overcome this shortcoming, an electromagnetic dynamic extruding film blowing system for mLLDPE was developed. A vibration force field was superposed on the entire extruding process through the screw. The die pressure, the screw load, and the power consumption decreased and the melt strength increased as the vibration frequency and amplitude increased, implying that the bubble stability enhanced, which resulted in the improvement of the processibility. In addition, experimental data show that the film strength in the transverse direction greatly increased and the film mechanical properties in machine and transverse directions became more uniform, so the film quality was improved finally. This rule was confirmed by using two additional materials, high‐density polyethylene and low‐density polyethylene. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 101: 83–89, 2006     

增容剂PE-LD-g-MAH对低密度聚乙烯／木质素共混体系性能的影响

研究了低密度聚乙烯(PE-LD)与马来酸酐(MAH)的接枝共聚物PE-LD-g-MAH对低密度聚乙烯/木质素共混体系微观形态、流变行为、热性能和力学性能的影响。DSC-TC综合热分析表明,添加增容剂的共混体系的熔融温度降低,热稳定性提高;流变性能分析表明,共混体系的加工性能良好;扫描电子显微镜(SEM)分析显示,添加增容剂后木质素分散相尺寸明显减小,分散程度提高;PE-g-MAH可以有效提高低密度聚乙烯/木质素吹塑薄膜的力学性能,且当木质素、低密度聚乙烯和PE-LD-g-MAH质量比为25/75/10时,力学性能最优。     

Mechanical properties of ultrahigh-molecular-weight polyethylene fiber-reinforced PE composites

Three types of high-strength polyethylene (PE) fiber-reinforced composite sheets were made by compression molding at the vicinity of melting point of the fiber. Sheet I was molded from only PE fibers. Sheets II and III were prepared by the compression molding of PE fiber with conventional high- and low-density polyethylene films, respectively. The mechanical properties, thermal behavior, and morphologies of the sheets have been investigated and compared with each other. The tensile strength and elastic modulus of sheet III are 660 MPa and 14 GPa, respectively, which were 60 and 30 times higher than those of typical low-density PE film. Although the elastic modulus of sheet III is 6 GPa less than that of sheet II, the tensile strength of 660 MPa is highest in the three types of sheets prepared in this study. The mechanical properties of sheets II and III were about half of predicted theoretical ones. It was concluded that the interfacial adhesion between PE fiber and PE matrix was an important factor to improve the mechanical properties of this PE sheet. © 1998 John Wiley & Sons, Inc. J Appl Polym Sci 68: 1431–1439, 1998     

Effect of addition of EVA on the technical properties of extruded foam profiles of low-density polyethylene/EVA blends

Some technical properties (static mechanical properties, dynamic mechanical properties, creep-recovery behavior, thermal expansion, and thermal conductivity) of low-density foams (50 kg/m³) made of blends of low-density polyethylene (LDPE) and the ethylene vinyl acetate copolymer (EVA) were studied as a function of the EVA proportion in the blends. These properties were compared with those of a foam made of a blend of EVA and ethylene propylene rubber (EPR). The knowledge of how the EVA proportion influences the behavior of these blend foam materials is a fundamental factor in order to obtain a wide range of polyolefin foams, with similar density, suitable for different applications. © 1998 John Wiley & Sons, Inc. J Appl Polym Sci 68: 1237–1244, 1998