Hot-pressed Films Research Articles

Studies on the Biaxial Stretching of Films, (part 24). Molecular Orientation and Mechanical Properties of Uniaxial and Biaxial Stretched Poly(methyl methacrylate) Films.

The relationship between molecular orientation and mechanical properties of poly (methyl methacrylate) films prepared by various types of stretching was investigated. The specimens were prepared by stretching the hot-pressed films to various ratios under two rates of 50 or 100%/min at 110-120°C in a circulating hot air bath. The Stretching methods were two types of uniaxial strechting with free and constant width, and simultaneous biaxial stretching. For the estimation of molecular orientation, the birefringence were measured using a tilting technique. Mechanical properties are discussed in terms of stress-strain curves.The following results were obtained:(1) The molecular orientation in the films uniaxially stretched with free width was uniaxial with cylindrical symmetry around the stretching axis, and the anisotropy of mechnical properties in the machine direction is greater than that of the other samples.(2) The uniaxially stretched films with constant width showed a uniplanar-axial orientation, in which the direction of molecular chain was parallel to the stretching axis and the film surface, Thus, Young's module were nearly equal in both the machine and transverse directions.(3) For the simultaneousbiaxially stretched films, the molecular chain showed a uniplanar orientation, which was a random orientation within the film along with parallel to film surface, at all stretch ratios. Mechanical properties of balanced films were isotropic in the film plane regardlless of the stretch ratio, and increased with stretching ratio.(4) On the transmittance of film for ultraviolet-visible radiation, all stretched films were slightly transparent than that of the unstretched film.

Effects of Molecular Weight of Nylon 6 on the Structure and Properties of Nylon 6/Poly(p-phenyleneterephthalamide) Molecular Composites

The effects of molecular weight of nylon 6 on the phase separation of nylon 6 in the molecular composites of nylon 6/poly(p-phenyleneterephthalamide) (PPTA) kept at 240°C and their mechanical properties related to molecular dispersity of PPTA have been studied on the coagulated and hot-pressed film. Crystallization of nylon 6 in the composites was studied by infrared spectroscopy, differential scanning calorimetry and X-ray diffraction. The crystallinity of nylon 6 was lost in the presence of PPTA when the PPTA content exceeds 50 wt% through all the range of molecular weight of nylon 6. The N-H stretching bands characteristic of PPTA and nylon 6 united to show a sharp single peak for the hot-pressed molecular composite for nylon 6 with MW=2.6×105, indicating the interruption of aggregation of PPTA molecules. The tensile modulus and strength were monotonously increased with increasing molecular weight of nylon 6 and weight fraction of PPTA in the composites. The improved dispersity of PPTA molecules gives outstanding mechanical properties to the molecular composite. The film strength was 170 MPa and the modulus was 12 GPa for the hot-pressed composite film of 10 wt% nylon 6 using its highest molecular weight.

Preparation and characteristics of dextran-methyl methacrylate graft copolymer

A graft polymer of dextran-methyl methacrylate (MMA) has been prepared using ceric nitrate. The solubility, infra-red absorption spectrum and thermal behaviour of the graft copolymer together with those of dextran and PMMA have been studied. It was found that a hot-pressed film of the copolymer not only shows better water wettability and water absorbing power than PMMA but also thrombo-resistance, and can be shaped into a transparent contact lens having an affinity for tears and blood. High resolution electron scanning microscopy shows that the surface of the contact lens has a micro-heterogeneous structure, consisting of phase separated grains of about 0.2 μm in size which are distributed uniformly.

Morphological studies of poly(olefin sulfones) by light scattering

Poly(olefin sulfones) are readily degraded by an electron beam and thus could be used as electron beam resists. However, films greater than 3000 A thick crack during formation and especially during solvent development following exposure to an electron beam. As crystallinity accentuates cracking owing to swelling stresses at the crystalline–amorphous interface, the morphology of various poly(olefin sulfones) was studies by light scattering. Materials investigated were solvent-cast and hot-pressed films of poly(butene-1 sulfone) (PBS), poly(cyclopentene sulfone) (PCPS), poly(bicycloheptene sulfone) (PBCHS), and two terpolymers of poly(cyclopentene sulfone–co–butene-1 sulfone), in which the molar ratios of cyclopentene to butene-1 were 50/50 (TP1) and 70/30 (TP2). All hot-pressed samples showed scattering patterns characteristic of randomly oriented rod-like superstructures 8–10 μm in length. Among the solvent-cast films, however, only PBS and TP2 samples scattered light indicative of crystallinity. Scattering from these samples were analyzed in terms of “random orientation fluctuation” light scattering theory. Correlation distances of 1.7 and 1.5 μm for the PBS and TP2, respectively, were obtained. The solvent-cast crystalline films (PBS and TP2) had a tendency to crack during dissolution as did the amorphous films of PCPS and PBCHS, indicating that cracking depends on the glass temperature as well as crystallinity. Only the amorphous terpolymer TP1 did not crack, presumably owing to its relatively low glass temperature effected by the butene-1 moiety.

EFFECT OF HEAT-AND MELT-TREATMENT ON DYE DESORPTION OF NYLON 6

The following samples of nylon 6 were prepared. Dyed film (DF); hot-pressed film was dyed at 100°C or 80°C with disperse dye (1, 4-diamino anthraquinone). Heat-treated film (HF); DF was heat-treated at 150°C for 5 hr. Melt-treated film (MF); DF was fused and quenched. The dye desorption in water at 70_??_100°C for above samples was measured, and compared with the dye absorption for the control sample treated by the same condition without dyestuff.The crystallinity of DF and HF are nearly same to that of their control samples, but the crystallinity from density method of MF is fairly higher than that of its control sample. The estimated non-desorbed residual dye content is zero for the sample dyed at 80°C and desorbed at 100°C, while that of the other samples increases in the order of DF MF>HF, and does not depend on the temperature of dyeing. Diffusion constant of the dye absorption is larger than that of the dye desorption especially for the heat-treated samples.

ISOMORPHISM AND DYNAMIC VISCOELASTICITY OF POLYESTER COPOLYMERS

Polyester copolymers were prepared by polycondensation of pairs of the following diacids with ethylene glycol: Terephthalic acid, sebacic acid, 1, 2-diphenoxyethane-p, p′-dicarboxylic acid (B), 1, 2-di (o-methylphenoxy) ethane-p, p′-dicarboxylic acid (M), and 1, 2-di (o-methoxyphenoxy) ethane-p, p′-dicarboxylic acid (V). The copolymers obtained and their hot-pressed films were subjected to following measurements; melting point, crystal spacing, density, crystallinity by X-ray method, glass-transition (Tg) and cold crystallization temperatures (Tcc) by DTA method, and dynamic viscoelasticity.From their melting points and crystal spacings, B-M, M-B and V-B copolymers are supposed to be isomorphous. Effects of isomorphism are observed in the following phenomena; smaller decrease in density and crystallinity, smaller increase in (Tcc-Tg), smaller decrease in half width and peak temperature of mechanical primary dispersion, smaller increase in dynamic modulus at 50°C, and smaller decrease in dynamic modulus at 120°C. Some discussion was made on these results.

ON THE STRUCTURE AND DYNAMIC VISCOELASTICITY OF NYLON COPOLYMERS

Nylon 66 copolymers and nylon 610 copolymers were prepared by substitutions up to 50mol% of aromatic diacid comonomers (terephthalic and isophthalic) and aliphatic diacid comonomers (adipic and sebacic). The resultant copolymers and their hot-pressed films were subjected to following measurements; intrinsic viscosity, melting point, crystal spacing, density, crystallinity by x-ray method, dynamic modulus, temperature of tanδ maximum, and value of tanδ maximum. It is suggested that the following structural characteristics affect the properties of copolymers; structural disorder by copolymerization, hydrogen bond concentration of homopolymer, rigidity and symmetry of comonomer molecule, and isomorphism. The isomorphous replacement which is observed only for nylon 66-6T copolymer decreases crystallinity and dynamic modulus at room temperature, which it increases temperature of tanδ maximum. The effect of moisture absorption on the dynamic viscoelasticity of copolymers was also studied. It is found that the depression of dynamic properties depend on the hydrogen bond concentration of copolymers.

RELATION BETWEEN MOLECULAR ORIENTATION AND MECHANICAL PROPERTIES OF STRETCHED POLYVINYLCHLORIDE FILMS

The relationship between the change in molecular orientation and the mechanical properties of polystyrene films prepared by various types of stretching was investigated. The specimens were prepared by stretching hot-pressed films to various ratios by different methods at 120°C and at a rate of 100%/min in a circulating hot air bath. The methods were uniaxial with the free and/or constant width, two-way successively biaxial and simultaneously biaxial stretching. For the estimation of the orientation the birefringences were measured by using a tilting technique and mechanical properties are discussed in terms of stress-strain curves.The following results were obtained:(1) The molecular orientation in the films uniaxially stretched with free width is uniaxial with cylindrical symmetry around the stretching axis, and the anisotropy of mechanical properties is greater than that of the others.(2) For the uniaxially stretched films with constant width, the orientation is roughly biaxial or uniaxial together with more or less planar orientation parallel to the film surface, Thus, the anisotropy of Young's modulus are nearly equal in both the machine and transverse directions.(3) For the two-way successive-biaxially stretched films, the “balance point of orientation” for the degree of chain orientation agree with the “balance point of mechanical properties” when the ratio of first and second stretchings are equal. Thus, the difference of mechanical property can be related to the difference of molecular orientation.(4) For the simultaneous-biaxially stretched films, the balanced mechanical properties, which are isotropic in the film plane, are independent of the stretch ratio. The molecular chain shows a random orientation within the film along with a planar orientation parallel to the film surface, as observed for other polymer films. The simultaneous-biaxial stretching is more excellent and preferable to successive-biaxial stretching for polystyrene film.