A Study on Preparation and Characteristics of Laminar Polymeric Film

• Main Authors: Chi-Hsien Huang, 黃啟賢
• Other Authors: Jiann-Shing Wu
• Format: Others
• Language: en_US
• Published: 2004
• Online Access: http://ndltd.ncl.edu.tw/handle/32597098118251949284

博士 === 國立交通大學 === 應用化學系所 === 92 === Laminar polymeric films are usually fabricated by coextrusion and blending processes. In a coextrusion process, a laminar polymeric film is formed into multilayer and parallel structures. In a blending process, on the other hand, the laminar polymeric film formed has laminar morphology of dispersed phases in its blend film. Because of the wide range of applications of laminar polymeric films as packaging materials, studies of the processes for forming, and the characteristics of, laminar polymeric films have become increasingly important. In this study, the aims are to predict the properties of the multilayer film and investigate the effect of adhesive on the laminar polymeric film. In Chapters 2 and 3, we successfully fabricated three-layer (A/B/C) films, comprising high-density polyethylene (HDPE), tie layer [high-density polyethylene-grafted maleic anhydride (HDPE-g-MAH]], and polyamide-6 (PA-6), by a coextrusion blown-film process. The tensile behavior of the three-layer film can also be predicted from its component layers by using an additive rule and an empirical constitutive equation —　, where σT, εT, and　 are the true stress, the true strain, and the true strain rate, respectively, K and γ ε are constants, and m is the strain rate sensitivity — and a simplified constitutive equation —　, where εT, σ0, and γ are the true strain, true yield stress and the strain hardening parameter, respectively — over the range of plastic deformation. There exists a good agreement between the experimental and predicted data at low crosshead speeds, but there is a relatively large discrepancy between them at high speeds, for both constitutive equations, because of the heat generated during deformation. The valid strain range for the latter is smaller, however, than that for the former. On the other hand, the series model was examined to predict permeability of HDPE/tie/ PA-6 three-layer film; there exists a good agreement between experimental data and this model for predicting both gas and water vapor permeabilities of three- layer films containing various volume fractions of PA-6. Conventionally, one or more tie layers are used in coextrusion processes, e. g., in the preparation of HDPE/tie/PA-6 mentioned above, but having additional tie layers in a coextruded film makes the fabrication process more complex and expensive. To eliminate the need for tie layer(s) and to reduce the number of layers, we have also successfully fabricated three-layer (A/B/A) films, comprising a varying content of ethylene–vinyl alcohol copolymer (EVOH) as the internal layer and blends of low-density polyethylene (LDPE) and adhesive [ low-density ethylene grafted with maleic anhydride (LDPE-g-MAH]] as the external layers, by a coextrusion blown-film process. In Chapter 4 ,we describe our investigation of the mechanical properties and compare their oxygen and water vapor permeabilities to a series model reflecting the content of adhesive. The peel strength increased sharply at LDPE-g-MAH content > 12.5 wt%; we associate this increase with a promotion of adhesion between layers that arises from the formation of ester bonds, as determined by FTIR spectroscopy, between EVOH and LDPE-g-MAH. The tensile strength did not change significantly upon increasing the LDPE-g-MAH content, but it had a small effect on elongation and modulus in both the machine and transverse directions. Tear strength decreased continuously, in both directions, upon increasing the LDPE-g-MAH content. The oxygen permeabilities of the three-layer films remained almost constant upon varying the amount of LDPE-g-MAH and all followed the series model. The water vapor permeabilities of the three-layer films, however, were affected by the degree of hydrogen bonding, which we analyzed by FTIR spectroscopy, to result in a discrepancy between the experimental findings and the series model, especially when the EVOH content was increased. An alternative process to fabricate laminar polymeric film is the blending process. In Chapter 5, we investigated the morphological, thermal, barrier, and mechanical properties of low-density polyethylene/ethylene–vinyl alcohol blend (LDPE/EVOH; 85/15 wt%) in highly and biaxially oriented blown films. We used linear low-density polyethylene-grafted maleic anhydride (LDPE-g-MAH) in various amounts as the compatibilizer for this immiscible system. Thermal analyses of the blend films indicated that their melting temperatures, crystallization temperatures, and heats of fusion remain almost constant upon varying the amount of compatibilizer. The addition of the compatibilizer did not adversely affect the inherent properties of the blends, especially their barrier properties, through constraint effects of the grafted EVOH (EVOH-g- LD). The heat of fusion of EVOH obtained during the first heating was much higher than that of the second as a result of the stress-induced crystallization that occurs during the blown-film process. Oxygen permeation measurements demonstated that the oxygen barrier properties of both highly and biaxially oriented blown films decrease upon increasing the amount of compatibilizer, although morphological analysis indicated that the blends exhibit better laminar dispersion of the EVOH phase in the LDPE. The increase in oxygen permeability results from the formation of microvoids at the interface between the two phases during the blown-film process. Mechanical measurements indicated that there exists an optimal amount of LDPE-g-MAH at which both the tensile and tear properties are maximized in both the machine and transverse directions.