The effect of surface roughness and crystallinity on the light scattering of polyethylene tubular blown films

An experimental study of the effect of surface roughness and crystallinity on the light scattering of polyethylene tubular blown films is reported. Several films were prepared by varying the raw polyethylenes and the extrusion temperature. Other processing variables were maintained constant. We have made a statistical analysis of data and we have obtained multiple regressions between light scattering for a given wavelength of incident light and a given film thickness (30 μm, 50 μm, and 70 μm) and the independent variables average surface roughness and degree of crystallinity. It was demonstrated that, for the polymeric films studied, the surface texture evaluates better than crystallinity the variation of light scattering, but crystallinity has also some importance.     

The effect of ultraviolet light on the mechanical properties of polyethylene and polypropylene films

Measurements were made of dynamic mechanical response spectra and stress–strain properties at room temperature on films of isotactic polypropylene and low-density polyethylene prior and after ultraviolet irradiation in a Xenotest 450 apparatus. The period of irradiation that caused a deep deterioration of ultimate mechanical properties influenced the dynamic mechanical properties only insignificantly. This is attributed to the heterogeneous nature of the photo-oxidative degradation process which is concentrated in a finite number of sites, thus forming crack precursors rather than changing the material properties in bulk. For a biaxially oriented tubular film of low-density polyethylene, anisotropic embrittlement after exposure in Xenotest 450 was observed. This even reversed the order of strain-at-break values in the two main directions of the film. This is remarkably similar to the effect of artificial incisions introduced into the specimens.     

The effect of crystallinity on the light scattering of regenerated cellulose tubular films

An experimental study of the effect of crystallinity on the light scattering of regenerated cellulose tubular films is reported. Several films were prepared by varying manufacturing conditions, so that thickness and surface roughness were maintained approximately constant and the degrees of crystallinity varied between 38 and 66%. The scattered radiation intensity, measured between 220 and 550 nm decreases with the increasing wavelength. It was demonstrated that for the polymeric films studied, there was excellent agreement between crystallinity and scattering radiation intensity for a given wavelength. It was found that for crystallinity values less than around 57%, scattered radiation intensity decreases with increasing crystallinity, the reverse of that for crystallinity values greater than that percentage.     

Light transmission and haze of polyethylene blown thin films

The surface and bulk morphologies of polyethylene blown films are obtained using non‐contact Atomic Force Microscopy (AFM). Based on these experimental observations, a model using the Mie Scattering theory is proposed to describe the forward transmission and scattering of a plane wave through the film. The light transmission properties are computed from the proposed model and the results are validated by experimental measurements.     

Oriented structure and anisotropy properties of polymer blown films: HDPE, LLDPE and LDPE

Different types of polyethylene blown films (HDPE, LDPE, LLDPE) differ significantly in the ratio between machine and transverse direction tear resistance. In this paper, low density polyethylene (LDPE), linear low density polyethylene (LLDPE) and high density polyethylene (HDPE) blown films at different draw-down ratios are studied, and the relation between crystalline structure and anisotropy of blown film properties is investigated. The crystalline morphology and orientation of HDPE, LDPE, LLDPE blown films were probed using microscopy and infrared trichroism. Significant differences in crystalline morphology were found: at medium DDR HDPE developed a row-nucleated type morphology without lamellar twisting, LDPE showed rod-like crystalline morphology and turned out to the row-nucleated structure with twisted lamellae at high draw-down ratio (DDR), while a spherulite-like superstructure was observed for LLDPEs at all processing conditions. They also showed quite different orientation characteristics corresponding to different morphologies. The morphologies and orientation structure for LDPE, LLDPE and HDPE are related to the stress applied (DDR) and their relaxations in the flow-induced crystallization process, which determine the amount of fibrillar nuclei available at the time of crystallization and therefore, the final crystalline morphology. These structure differences are shown to translate into different ratios of machine and transverse direction tear and tensile strengths.     

Morphological considerations on the mechanical properties of blown high-density polyethylene films

Blown films having a broad range of morphologies were prepared from high-density polyethylenes (HDPE) with unimodal and bimodal molecular weight distribution under several processing conditions, and the effect of their morphological features on the dart drop impact resistance, Elmendorf tear strength, and tensile properties of the films has been studied. The organization of lamellar stacks seems to play a critical role on the mechanical properties of the blown HDPE films. The dart drop impact resistance of the blown HDPE films is highly dependent on the presence of the network structure of lamellar stacks and the level of the intraconnectivity and interconnectivity of lamellar stacks. The coherent orientation of lamellar stacks leads to significant anisotropy of tear and tensile properties. © 1997 John Wiley & Sons, Inc.     

Effects of fillers on permeability and mechanical properties of HDPE blown films

HDPE compounds containing various amounts of rigid (platy talc) or deformable (nylon-6) oxygen barrier components were blended in a twin-screw extruder and processed into thin films by blown film extrusion. The films were tested for oxygen permeability and mechanical properties and analyzed for morphology. Optimization of barrier component content is shown to depend on the desired permeability level, film ductility and processability.     

HDPE/LLDPE/POE薄膜性能的研究

采用线型低密度聚乙烯（LLDPE）和热塑性弹性体乙烯-辛烯共聚物（POE）对高密度聚乙烯（HDPE）薄膜进行改性,研究了LLDPE和POE对共混体系薄膜力学性能、加工性能的影响,探讨了LLDPE增强HDPE的机理。结果表明,加入一定量LLDPE,使HDPE／LLDPE薄膜的拉伸强度较纯HDPE薄膜有所增加,而单位冲击破损质量则有所下降。当w（LLDPE）为15％时,HDPE／LLDPE薄膜的拉伸强度提高21．6％,薄膜的单位冲击破损质量降低23．0％。在HDPE／LLDPE/POE三元体系中,当w（POE）,w（LLDPE）分别为10％,15％时,薄膜的拉伸强度、单位冲击破损质量、断裂伸长率比纯HDPE薄膜分别提高2．3％,113％。36．0％,综合性能良好。     

The development of surface texture in blown polypropylene film

The reorganization processes that give rise to surface fibrillation in blown polypropylene film are described in some detail with the aid of numerous photomicrographs. A relationship between stalk surface morphology and degree of surface roughness is noted.     

成核剂对聚丙烯性能的影响

研究了各种α晶型成核剂和β晶型成核剂对聚丙烯性能的影响,发现用α晶型成核剂NA-11和用N催化剂生产的高等规指数聚丙烯组合,可制成透明型高强度、高耐热聚丙烯。这种高性能聚丙烯在家电、汽车等方面具有极为广泛的应用前景。     

Heat sealing of semicrystalline polymer films. I. Calculation and measurement of interfacial temperatures: Effect of process variables on seal properties

A finite element analysis (FEA) modeling technique was used to predict the interfacial temperature as a function of time during the sealing of semicrystalline polymer films. An experimental technique using micro-thermocouples to measure rapidly changing interfacial temperatures during sealing was also developed. Agreement between predicted interfacial temperature profiles and measured values for polyethylene films was good except at temperatures substantially above the final melting point of the polymer. This deviation is caused by film-thickness changes occurring during sealing that are not taken into account in the calculations. The effect of heat-sealing process variables (seal bar temperature, dwell time, and pressure) on seal properties (seal strength, seal elongation, and seal energy) of polyethylene films has also been quantitatively determined. Seal properties are determined primarily by the maximum temperature achieved at the interface during heat sealing. Dwell time must be sufficiently long to bring the interfacial temperature to a desired level, but longer times at a given interfacial temperature do not improve seal properties at the conditions of our experiments. A slight pressure is helpful in bringing two microscopically uneven film surfaces into intimate contact, but higher pressure has no beneficial influence on seal properties. However, increased pressures and dwell times at temperatures above the final melting point of the polymer are detrimental to seal appearance due to material deformation in the sealing area. © 1994 John Wiley & Sons, Inc.     

The effect of variations in light intensity on the photo-oxidation of polypropylene

When polypropylene foil was photo-oxidized in a laboratory UV aging apparatus, the rate of photo-oxidation was proportional to various fractional powers of the light intensity depending on the type of lamp(s) used and whether the polymer was stabilized or unstabilized.     

Evidence for the reduction of quinones added during thermal processing of polypropylene and the resultant effect on polymer light stability

The thermal and photochemical oxidation of anthraquinone- and p-benzoquinone-doped polypropylene has been studied by absorption, luminescence, and infrared spectroscopy. Prior to irradiation, fluorescence and phosphorescence measurements showed that some of the anthraquinone and most of the p-benzoquinone had been converted into their corresponding hydroquinones during processing. The p-benzoquinone, unlike anthraquinone, also imparted a blue coloration to the polymer before irradiation, which is associated with the formation of a quinhydrone complex (or complexes). These results indicate that the quinones are thermally reduced to their corresponding hydroquinones during processing by a mechanism of hydrogen atom abstraction from the polymer substrate. On photo-oxidation, whereas anthraquinone acted as a photosensitizer, p-benzoquinone acted as a photostabilizer.     

送电曲线对石墨化过程的影响

通过改变石墨化过程中的送电曲线,从而改变炉内产品的升温速率。对比改变曲线前后产品性能,发现采用新曲线后,不仅每吨产品的耗电量有明显下降,而且产品的电阻率有很大幅度提高,达到减少送电时间、提高生产效率、降低石墨化制品电耗和改善产品性能指标的目的。     

Influence of molecular architecture and melt rheological characteristic on the optical properties of LDPE blown films

A systematic investigation on the origin of the haze of LDPE blown films was conducted, aiming to correlate the film haze with the molecular architecture and melt rheological properties. First of all, the haze measurement indicated that the surface haze, rather than the bulk haze, is the dominating factor for the total haze of the investigated films. No spherulitic crystals or other superstructures were observed for the LDPE blown films, implying that the crystallites formed in the film-blowing process are too small to be responsible for the optical haze. Rheological study revealed that the surface roughness was originated from the irregular flow of LDPE melt during the extrusion process. NMR, GPC and parallel-plate rheology were applied to study the molecular architecture of the LDPE resins. It was found that the LDPE sample with higher haze value exhibits distinctly larger portion of higher molecular weight component, broader molar mass distribution, significantly higher side chain branch density.     

The effect of addition of high-density polyethylene on the crystallization and mechanical properties of polypropylene and glass-fiber-reinforced polypropylene

High-density polyethylene up to about 30% by weight was melt-mixed with polypropylene and short-glass-fiber-reinforced polypropylene. The presence of high-density polyethylene and glass fibers in the polypropylene matrix affects its crystallization characteristics, which were studied with the help of differential scanning calorimetry. The blend and composite samples have a large number of polypropylene domains apparently due to an abundance of surface nuclei; as a result, the tensile strength, tensile modulus, and toughness are enhanced. The temperature dependence of shear modulus and logarithmic decrement indicate that high-density polyethylene can have plasticizing effect below the glass transition temperature of polypropylene. The scanning electron micrographs of fractured ends show the presence of dispersed domains in the composite samples.     

Some mechanical properties of solvent-treated polypropylene films

The amount of polypropylene (PP) extracted by hot solvent extraction increased with increasing naphtha in a naphtha/reformate solvent blend. The stress–strain curves formed the basis for the calculation of several mechanical properties of the residual film. The yield stress, the natural draw ratio, secant modulus, breaking factor, and work expended in drawing were maximum at a 10/90 naphtha/reformate composition. These were explained in terms of extraction of low molecular weight and atactic materials leaving a more stereoregular block, giving maximum properties with the least removal of polymer materials. Further increases in the naphtha component, however, decreased these properties, possibly due to the greater solubilizing effect of naphtha for the PP chains. © 1995 John Wiley & Sons, Inc.     

Excluded volume effect on polymer films

Using Monte Carlo methods we have investigated the excluded volume effect on polymer melts in two dimensions. Investigating chain lengths of up to N = 59 at concentration $\text{c =}\text{5}\text{6}$, our results strongly support predictions made recently by de Gennes: (1) end-to-end distance and gyration radius exhibit Gaussian behaviour ∝ √N; (2) but their prefactors differ significantly from their random flight values; (3) in contrast to three-dimensional melts the chains are strongly segregated.