Optimization of PE/Binder/PA extrusion blow‐molded films. I. Heat sealing ability improvement using PE/EVA blends

The optimization of three‐layer films (PE/binder/PA) manufactured by extrusion blow molding presents significant industrial challenges. The main issue consists in combining use properties (e.g., impermeability to water steam and oxygen, welding properties) with high mechanical, optical, and adhesion performances, while maintaining cost‐effectiveness. This article shows that the introduction of EVA in the PE layer improves the heat sealing ability and optical properties without degradation of the mechanical and adhesion performances. In the most favorable case, this modification leads to a 40% reduction of the heat sealing time, the other performances remaining either identical or higher. This leads to cost reduction of this manufacturing step while improving the flexibility of the process (wider process temperature window). The properties modifications observed can be explained by microstructure modifications (crystallinity, orientation, and molecular mobility). © 2005 Wiley Periodicals, Inc. J Appl Polym Sci 99: 974–985, 2006     

Preparation of HDPE/UHMWPE/MMWPE blends by two-step processing way and properties of blown films

Summary Blends of high density polyethylene (HDPE) and ultra high molecular weight polyethylene (UHMWPE) were prepared by two-step processing way. Middle molecular weight polyethylene (MMWPE) as a fluidity modifier and compatilizer was added into UHMWPE in the first step, and then modified UHMWPE and HDPE were blending extruded to prepare the HDPE/UHMWPE/MMWPE blends used for blown films. The mechanical test of the blown films revealed that when the content of MMWPE in modified UHMWPE was 40wt% and the content of UHMWPE in the blends was 20 wt%, the film had the optimal mechanical properties. The tensile strength and tear strength of the film increased by 50% and 21%, respectively, compared with those of pure HDPE film. Rheological curves indicated that the melt torque and the apparent viscosity of the HDPE/UHMWPE/MMWPE blends made by two-step processing way both greatly reduced than other blends. The results from DSC suggested that the blends by two-step processing way may form more stable and perfect co-crystallization. PLM (polarized light microscopy) and SEM micrographs revealed that two-step processing way can improve the surface morphology of the films and make the dispersion of UHMWPE particles in HDPE increase.     

Optimization of PE/binder/PA extrusion blow‐molded films. II. Adhesion properties improvement using binder/EVA blends

The second part of this series shows that the incorporation of EVA in the tie layer of extrusion blow‐molded three‐layer (PE/binder/PA) improves the adhesion properties, while reducing the film cost by 6% and preserving the performances previously (Part I) obtained by addition of EVA in the PE layer only, such as optimal improved seal ability, optical properties, and satisfactory mechanical properties. The improvement of adhesion between the binder and the PA layers could be related to a modification of the type and the density of the intermolecular interactions between binder, PA, and EVA. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 2006     

Measurement of the adhesion of diamond films on tungsten and correlations with processing parameters

Adhesion between diamond films and tungsten substrates is reported as a function of the deposition processing parameters. Diamond films were grown by a hot filament method as a function of seven different processing parameters: substrate scratching prior to diamond deposition, substrate temperature, methane content of the input gas mixture, filament temperature, filament-substrate distance, system pressure, and total gas flow rate. Adhesion was measured by using a Sebastian Five A tensile pull tester. Testing was complicated by the non-uniformity of the film thickness, diamond quality, film cohesion, and surface preparation across the full substrate surface area. Various types of film failure mode were observed, which did not correlate with the film processing parameters. The measured adhesion values showed larger variations from point to point across the sample surface and from identically prepared samples than variations as a function of the film processing parameters. Weak correlations of adhesion with the processing parameters were found using statistical analysis of the results from multiple pulls on a large number of samples. The statistical results suggest that substrate preparation, gas flow rate, and gas pressure are the most important processing parameters affecting the film adhesion, while the temperature of the hot filament has little or no effect on the adhesion of the film. However, improvements in film processing and adhesion testing need to be made before true quantitative adhesion testing of high-quality diamond films can be accomplished.     

含稳态氦氧自由基的光稳定剂对PE／EVA薄膜老化性能的影响

合成了含稳态氮氧自由基的光稳定剂，其结构通过ESR、元素分析表征，考察了其热稳定性。将其与聚乙烯（PE）／乙烯-醋酸乙烯酯共聚物（EVA）共混吹塑薄膜，经过紫外灯照射进行加速老化后，考察该含氮氧自由基的光稳定剂的光稳定性能，对比了不同试样老化前后的力学性能、羰基指数和透光率的变化。结果表明：含稳态氮氧自由基的光稳定剂在367℃才开始迅速分解，热稳定性良好，能够满足成型加工的各项要求；添加含稳态氮氧自由基光稳定剂的PE／EVA薄膜经过紫外光照射后的力学性能明显优于没有添加任何光稳定剂的和添加了同样用量的Chimassorb 944的PE／EVA薄膜；透光率衰减的速率与加入Chimassorb 944的薄膜透光率衰减速率几乎一样，但是透光率要高于添加Chimassorb 944的薄膜。     

Mechanical properties,thermal stability,and thermal degradation kinetics of silicone rubber/ethylene-vinyl acetate copolymer/magnesium sulfate whisker composites compatibilized by ethylene-acrylic acid copolymer

Silicone rubber/ethylene-vinyl acetate copolymer/magnesium sulfate whisker composites containing ethylene-acrylic acid copolymer (MS/SR/EVM/EAA) as a compatibilizer were successfully prepared. Moreover, the magnesium sulfate whisker surface was modified with 3 wt% of silane coupling agent (KH570), resulting in composites including (unmodified magnesium sulfate whisker) uMS/SR/EVM, (modified magnesium sulfate whisker) mMS/SR/EVM, and mMS/SR/EVM/EAA were compared. The values of thermal decomposition activation energy (E_a) calculated by the two different methods (Kissinger and Friedman methods) show that the composites filled with 5 and 20 phr whiskers have lower values of activation energy (E_a) than the SR/EVM blend. The tensile strength of composites with a 5 phr modified whisker is 14.5 MPa, which is higher than that of the SR/EVM blend and uMS5/SR/EVM composite. The tear strength of the composite with 20 phr mMS is 51.6 kN m⁻¹, much higher than that of the composite with 20 phr uMS and SR/EVM blend. The mechanical properties were also investigated after thermal aging of the composites at 85°C for 48 h. The thermal conductivity of the composites with high filler loading was studied.     

Interfacial processing and adhesion of diamond,diamond-like,and TiN films on metallic and polymeric substrates

Diamond, diamond-like, and titanium nitride (TiN) films have extremely desirable chemical, electrical, and mechanical properties for a variety of applications ranging from corrosion- and erosion-resistant coatings to electronics packaging of microelectronic devices. However, many of these applications are limited by the poor adhesion of these films to metal and polymer substrates. The adhesion of a film is determined primarily by internal stresses in the film, thermal and lattice mismatch, and most importantly by interfacial bonding. We have developed methods based on mechanical interlocking, chemical bonding, grading of interatomic potentials, and the multilayer discontinuous thin films approach to control stresses and strains in thin films. A substantial improvement in adhesion and wear properties is obtained by using these methods selectively. We review issues related to the adhesion of diamond, diamond-like carbon, and TiN films on metal and polymeric substrates.     

动态交联PP/EVA共混物的制备与性能研究

本文将动态交联技术应用于PP/EVA共混体系中,制得动态交联PP/EVA共混物。采用Hakke转矩流变仪研究了动态交联对PP/EVA共混物扭矩的影响;研究了DCP和EVA含量对共混物力学性能的影响;考察了动态交联共混物的维卡软化点。结果表明：加入DCP后,PP/EVA共混物扭矩先升后降,DCP的添加量为EVA含量的1%为宜。随EVA用量的增加,动态交联EVA/PP共混物的冲击强度大幅提高,但拉伸强度有所降低。少量经动态交联的EVA颗粒可以促进共混物中PP的结晶, 提高共混物的维卡软化点。     

含稳态氮氧自由基的光稳定剂对PE／EVA薄膜老化性能的影响

合成了含稳态氮氧自由基的光稳定剂,其结构通过ESR、元素分析表征,考察了其热稳定性。将其与聚乙烯 (PE)／乙烯-醋酸乙烯酯共聚物(EVA)共混吹塑薄膜,经过紫外灯照射进行加速老化后,考察该含氮氧自由基的光稳定剂的光稳定性能,对比了不同试样老化前后的力学性能、羰基指数和透光率的变化。结果表明:含稳态氮氧自由基的光稳定剂在367℃才开始迅速分解,热稳定性良好,能够满足成型加工的各项要求;添加含稳态氮氧自由基光稳定剂的PE／EVA薄膜经过紫外光照射后的力学性能明显优于没有添加任何光稳定剂的和添加了同样用量的Chimassorb 944的PE／EVA薄膜;透光率衰减的速率与加入Chimassorb 944的薄膜透光率衰减速率几乎一样,但是透光率要高于添加Chimassorb 944的薄膜。     

EVA/MCA复合体系的燃烧性能与炭层结构

以乙烯-乙酸乙烯酯共聚物(EVA)为基体树脂,以氰尿酸三聚氰胺(MCA)为阻燃剂,研究了EVA/MCA复合体系的燃烧性能,并对燃烧炭层进行了分析.结果表明,MCA改善了EVA/MCA体系的燃烧性能,消除了燃烧滴落现象,抑制了黑烟的产生.随着MCA添加量逐渐增大,氧指数由18.0%提高到26.1%,当MCA添加量为80质量份时,体系成为难燃材料.当MCA添加量分别为50,60,80质量份时,EVA,MCA复合体系的阻燃级别依次可以达到FV-2级,FV-1级,FV-0级.随着MCA添加量的增加,燃烧试样表面的炭层逐渐增多,致密程度提高;随着燃烧时间的增加,燃烧试样内部的孔洞增多,孔径变大.     

EHA/PE复合薄膜的力学性能和阻透性能

分别使用氧气透过率分析仪、水蒸气透过率分析仪、拉伸试验机、紫外可见分光光度计以及差示扫描量热仪测试了乙烯乙烯醇共聚物(EVOH)、聚酰胺6(PA6)、EVOH/PA6(EHA)等薄膜以及EHA/聚乙烯(PE)复合薄膜的力学性能和阻透性能。结果表明,EVOH与PA6有较好的相容性,所制成的薄膜EHA与PE复合后的EHA/PE复合薄膜对氧气和水蒸气有良好的阻隔性,并且对可见光有很好的透过性,比较适合作食品包装材料。     

Effect of poly(ethylene methyl acrylate) copolymer on thermal,morphological, and mechanical properties of polypropylene copolymer blown films

Blends of polypropylene copolymer (PP‐cp) and poly(ethylene methyl acrylate) [poly(EMA)] copolymer blends were processed by blown film extrusion. The orientation and crystallinity of PP‐cp matrix in the blend did not change significantly with the addition of EMA. The low machine direction and transverse direction tear strengths, which are observed for neat polypropylene blown films more than doubled at 6 wt % or higher content of EMA. The increase in tear properties was mainly attributed to a fine dispersion of EMA in the matrix with an average particle size of 100–500 nm and the formation of elongated domains. The dispersed nonrounded EMA domains, resulting from the blown‐film process, enhance better energy dissipation mechanism with the formation of an extended plastic zone in the blend films as compared with that in pure PP‐cp films. © 2007 Wiley Periodicals, Inc. J Appl Polym Sci, 2008     

热封温度对PET/Al/PE包装膜热封性能的影响

设计多种实验工况研究热封工艺参数对聚对苯二甲酸乙二酯(PET)/Al/聚乙烯(PE)复合薄膜热封强度的影响.结果表明,热封温度对热封强度的影响最为显著.在此基础上,采用扫描电子显微镜和拉伸破坏模式对热封区域表观判定,采用差示扫描量热法分析热封材料PE的热性能,并结合工程实际,确定PET/Al/PE有效热封温度为110～160℃.     

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.     

Rheological,mechanical, optical,and transport properties of blown films of polyamide 6/residual monomer/montmorillonite nanocomposites

Exfoliated nanocomposites of polyamide 6 (PA6) with residual monomer and an organically treated montmorillonite (3 and 5 wt %) were produced by twin‐screw extrusion. The composites had their steady state, dynamic, and transient rheological properties measured by parallel‐plates rheometry; their exfoliation level was characterized by wide angle X‐rays diffraction (WAXD) and transmission electron microscopy (TEM). The characterization showed as follows: (i) the nanoclay's lamellas were well dispersed and distributed thru the PA6, (ii) the postpolymerization of the residual monomer produced more branched chains than linear ones in the pure PA6, (iii) the nanoclay's lamellas acted as entanglement points in the nanocomposites, and (iv) the molecular weight of the PA6 in the nanocomposites decreased. Blown films of the nanocomposites were produced by single screw extrusion; the die pressure during the film blowing of the nanocomposites strongly decreased. The tensile mechanical properties of the blown films were also measured. Along the machine direction (MD), the best mechanical properties were obtained with the 5 wt % nanocomposite, whereas along the transverse direction (TD), the 3 wt % nanocomposite had the best behavior. The glass transition temperature (T_g) of the blown films was measured by dynamic mechanical thermal analyses (DMTA). The 5 wt % nanocomposite had the highest T_g of all the films. The optical properties were measured by spectrophotometry; the nanoclay decreased the films' haze, but the level of transmittance was not affected. The water vapor and oxygen permeability rates of the nanocomposites films were found to be lower than in the pure PA6 blown film as a result of a tortuosity effect. © 2010 Wiley Periodicals, Inc. J Appl Polym Sci, 2010     

The effect of heat sealing temperature on the properties of OPP/CPP heat seal. I. Mechanical properties

The effect of heat sealing temperature on the mechanical properties and morphology of OPP/CPP laminate films was investigated. The laminated films were placed in an impulse type heat sealing machine with both CPP sides facing each other. The temperatures investigated ranged from 100 to 250°C. T‐peel and tensile tests in combination with SEM were used to characterize the heat seals. A minimum seal initiation temperature of 120°C was identified for OPP/CPP laminate heat sealing. Peel strength increased sharply from zero at 110°C to maximum at 120°C, after which a gradual decrease was observed. Tensile strength initially increased until 120°C, after which it gradually decreased until 170°C and assumed a constant value beyond that. The initial rise has been associated to cold crystallization, while the reduction between 120°C and 170°C was due to relaxation in molecular orientation. Beyond 170°C, all the orientation in the laminate has been lost so orientation effects are nullified. Morphological studies with SEM revealed that seals were partially formed at lower temperatures, while the laminates were totally fused together at high temperatures, with intermediate temperatures showing properties that lie in between. © 2005 Wiley Periodicals, Inc. J Appl Polym Sci 97: 753–760, 2005     

Synthesis of a pyrene-functionalized hyperbranched polyethylene ternary copolymer for efficient graphite exfoliation in chloroform and formation of ethylene-vinyl acetate/graphene nanocomposites

A strategy for preparing ethylene-vinyl acetate (EVA)/graphene nanocomposites from liquid-phase exfoliated graphene has been explored with the use of a pyrene-functionalized hyperbranched polyethylene (HBPE) ternary copolymer, HBPE@Py@PMA, as stabilizer for graphite exfoliation. The HBPE@Py@PMA was synthesized by combining the Pd-diimine-catalyzed chain walking ternary ethylene copolymerization and atomic transfer radical polymerization techniques and has been confirmed to possess a HBPE core simultaneously bearing pyrene terminal groups and polymethacrylate side chains. As stabilizer, it is found to effectively promote graphite exfoliation in CHCl₃ to render high-quality few-layer graphene with an efficiency as high as 43%. Meanwhile, it can be steadily adsorbed on the exfoliated graphene surface to concurrently render functionalized graphene well dispersible in EVA matrix with strong interfacial interactions. This allows us to obtain EVA/graphene nanocomposites from resulting graphene dispersion through simple solution mixing process. By adding only 0.5 wt% of graphene, the dielectric constant of resulting composite increases by 55% compared to pure EVA, with a dielectric loss only 0.012. The role mechanism of the HBPE@Py@PMA for promoting graphite exfoliation in CHCl₃ and the formation of EVA/graphene nanocomposites from the resulting graphene has been proposed.     

Structure and properties of starch/poly(ethylene-co-vinyl alcohol) blown films

Blends of native corn starch and poly(ethylene-co-vinyl alcohol) (EVOH), with starch: EVOH ratios of 1 : 1 (SE-50) and 2 : 1 (SE-67A, SE-67B), were processed into blown films. SE-67A had a higher glycerol and water content and was processed at 5°C higher than was SE-67B. The films were conditioned to various moisture contents by equilibrating at a constant relative humidity and by oven drying at 41°C. Equilibrium moisture content, which ranged from 2 to 11%, increased with increasing starch content at a given relative humidity. Mechanical properties depended strongly on starch and moisture content as well as on processing history. The extension to break of SE-50 was only about one-third that of EVOH, while that of the 2 : 1 blends was even lower. SE-67A exhibited a higher extension to break, lower tensile strength and modulus, and greater moisture sensitivity than those of SE-67B. Differential scanning calorimetry and dynamic mechanical analysis revealed evidence of interactions between starch and EVOH, probably indicative of extensive intermixing but not necessarily miscibility. Scanning electron micrographs of fracture surfaces revealed extensive differences in texture with microcracking in SE-50 and SE-67A. The combination of the analytical results provide a basis for explaining many aspects of the mechanical behavior including the marked difference in properties between SE-67A and SE-67B. © 1997 John Wiley & Sons, Inc. J Appl Polym Sci 64: 2613–2622, 1997     

Peeling of heterogeneous thin films: Effect of bending stiffness,adhesion energy,and level of heterogeneity

The peeling behaviour of a heterogeneous thin film bonded to a rigid substrate was investigated by using both experiments and finite element modeling. The enhancement in peel force was studied specifically for heterogeneous thin films with periodic stiff and compliant portions along the length. Peel tests with homogeneous thin films (uniform film thickness) showed that the maximum peel force can be observed before the onset of steady state peeling process. Moreover, this maximum peel force was observed to be a function of the bending stiffness of the film and adhesion energy at the film-substrate interface. For the heterogeneous thin films, maximum peel force can be observed either before the onset of steady state or when the peel front traverses from compliant to the stiff portion of the film. The three-dimensional finite element model, based on cohesive zone technique was developed, which provided further insight into the enhancement in peel force. The maximum force was shown to be dependent on the level of heterogeneity in addition to adhesion energy and bending stiffness as was observed with homogeneous films. The improvement in peel force was found to be prevalent at relatively low adhesion energy. This study may be helpful for the better design of homogeneous and heterogeneous thin film-substrate systems having improved bonding strength.     

Thickness and composition dependence of the glass transition temperature in thin random copolymer films

Glass transition temperatures (T_g) of thin poly(styrene-co-methyl methacrylate) and poly(2-vinyl pyridine-co-styrene) films coated on a native oxide surface of Si wafer (100) were measured by ellipsometry. The thickness dependence of T_g can be properly fitted by previously suggested equation developed for homopolymers, based upon a continuous multi-layer model, although one component in thin random copolymer films demonstrates a slightly favorable interaction between a substrate and thin film, and another demonstrates a strongly favorable interaction. Surface and interface have a strong influence on T_g of thin film coated on substrate: the surface has the effect of reducing T_g, whereas the interface increases the T_g according to the degree of interaction between a substrate and thin film. This degree of interaction can be quantified as an interaction parameter (k), and is dependent on the composition of random copolymers. For the estimation of k values of thin random copolymer films, we proposed a parallel type additive function (1/k_ran=w₁/k₁+w₂/k₂) where w is a weight fraction of component.