Byung Chul Ji

Effects of polymer concentration and zone drawing on the structure and properties of biodegradable poly(butylene succinate) film

To produce various biodegradable poly(butylene succinate) (PBS) films for particular use, the effects of initial polymer concentration and zone drawing on the structure, physical properties, and hydrolytic degradation of PBS film were investigated. PBS films were prepared from chloroform solutions with different initial concentrations of 8, 11, 14, 17 and 20 g/dl. In order to investigate the drawing behavior of the PBS films with different solution concentrations, the films were drawn under various zone drawing conditions. Through a series of experiments, it turned out that the initial concentration of PBS solution in chloroform caused significant changes in the draw ratio of the PBS film. That is, the zone draw ratios of the film at initial concentration of 14 g/dl exhibited its maximum values and gradually decreased at higher or lower concentrations. Thus, it was concluded that the initial concentration of 14 g/dl is the optimum polymer concentration to produce maximum draw ratio in this work. In addition, the crystal and amorphous orientations and tensile properties of PBS film having similar draw ratio and similar crystallinity were highest at 14 g/dl and surface crystal morphologies of these films were absolutely different. The hydrolytic degradation rate of the film at 14 g/dl was lowest, but with similar draw ratio, film dimension, and crystallinity, indicating that the degradation behaviors were greatly affected by the initial polymer concentration, orientation, and crystal morphology.

Syndiotacticity-rich ultrahigh molecular-weight poly(vinyl alcohol) film. I. Determination of optimum polymer concentration by zone-drawing method in film preparation

A new method using a simple zone-drawing technique has been suggested for determining the optimum initial concentration of a polymer solution that has suitable macromolecular entanglements. This method was developed to replace the incorrect inherent viscosity-measuring method for syndiotacticity-rich (syndiotactic diad content of 63.4%) ultrahigh molecular-weight (number-average degree of polymerization of 12,300) (UHMW) poly(vinyl alcohol) (PVA) solution. Syndiotacticity-rich UHMW PVA films were prepared from dimethyl sulfoxide (DMSO) solutions with different initial concentrations: of 0.1, 0.2, 0.3, 0.4, and 0.5 g/dL. In order to investigate the drawing behavior of the syndiotacticity-rich UHMW PVA films with different solution concentrations, the films were drawn under various zone-drawing conditions. Through a series of experiments, it was discovered that the initial concentration of PVA solution in DMSO caused significant changes in the draw ratio of the syndiotacticity-rich UHMW PVA film. That is, the one-step and maximum zone draw ratios of the film at an initial concentration of 0.3 g/dL exhibited its maximum values and gradually decreased at higher or lower concentrations. Thus, it was disclosed that the initial concentration of 0.3 g/dL is the optimum polymer concentration to produce a maximum draw ratio in this work. Based on the above results, it may be concluded that the optimum concentration of the initial PVA solution can be determined directly by measuring the zone draw ratio. The draw ratio, birefringence, crystallinity, degree of crystal orientation, tensile strength, and tensile modulus of the maximum drawn PVA film were 32.9, 0.0449, 0.61, 0.991, 1.91, and 46.2 GPa, respectively.

Preparation of poly(vinyl acetate)/clay and poly(vinyl acetate)/poly(vinyl alcohol)/clay microspheres

Poly(vinyl acetate) (PVAc)/poly(vinyl alcohol)(PVA)/montmorillonite (MMT) clay nanocomposite microspheres with a core/shell structure have been developed via a suspension polymerization approach. In order to prepare the PVAc/MMT and PVAc/PVA/MMT nanocomposite microspheres, which are promising precursor of PVA/MMT nanocomposite microspheres, suspension polymerization of vinyl acetate with organophilic MMT and heterogeneous saponification were conducted. A quaternary ammonium salt, cetyltrimethylammonium bromide, was mixed with the MMT in the monomer phase prior to the suspension polymerization. The rate of conversion decreased with an increase in MMT concentration. The incorporation of MMT into the PVAc was verified by FT-IR spectroscopy. Organic vinyl acetate monomers were intercalated into the interlayer regions of organophilic clay hosts and followed by suspension polymerization. Partially saponified PVA/MMT nanocomposite microspheres with a core/shell structure were successfully prepared by heterogeneous saponification.

Preparation and characterization of syndiotacticity-rich ultra-high molecular weight poly(vinyl alcohol)/imogolite blend film

To enhance the physical properties of syndiotacticity-rich (syndiotactic diad content 63·4%) ultra-high molecular weight (UHMW) (number-average degree of polymerization 12300) poly(vinyl alcohol) (PVA) film, it was solution blended with rigid-rod imogolite in dimethyl sulphoxide. In addition, the blend film prepared was stretched using a high-temperature zone drawing technique for effective orientation of the film. Through a series of experiments, it was found that imogolite caused significant changes in the structure and properties of syndiotacticity-rich UHMW PVA film, i.e. imogolite acted as an important agent which increased crystal orientation of syndiotacticity-rich UHMW PVA, resulting in enhanced tensile strength of the film. However, imogolite played a hindering role in raising the amorphous orientation of syndiotacticity-rich UHMW PVA. The maximum tensile modulus of 19·8GPa and maximum tensile strength of 1·8GPa could be obtained at the maximum draw ratio of 7·45 for PVA/imogolite blend film. In the case of PVA homo film, the highest tensile modulus and strength were 25·2GPa and 1·4GPa, respectively.

Effect of zone drawing accompanied with crosslinking on the structure and properties of ultrahigh molecular weight polyethylene gel film

To enhance the thermal properties of ultrahigh molecular weight ( UHMW ) (viscosity-average molecular weight of 6 x 10 6 ) polyethylene (PE) gel film, this was crosslinked by dicumyl peroxide ( DCP ) during a high-temperature zone drawing, which is effective to orient film. Through a series of experiments, it turned out that crosslinking actualized by an optimum amount of DCP and high-temperature zone drawing technique caused significant changes in the structure and properties of UHMW PE gel film. That is, crosslinking increased storage modulus of UHMW PE gel film at 25°C, resulting in improving thermal properties of the film. On the contrary, the crosslinking effect played a hindering role in raising the draw ratio of UHMW PE gel film. Maximum storage modulus of 165 GPa at 25°C could be obtained at the draw ratio of 324 of uncrosslinked homo-PE gel film. In the case of crosslinked PE gel film, the highest storage modulus at 25°C reached 65 GPa at maximum draw ratio of 150. Crosslinked film exhibited high modulus, even at 190°C, to some extent, while uncrosslinked homo-PE gel film was molten completely at 150°C.

THE PHYSICAL PROPERTIES OF POLY(2-HYDROXYETHYL METHACRYLATE) COPOLYMER HYDROGELS USED AS INTRAVAGINAL RINGS

Poly(2-hydroxyethyl methacrylate) (PHEMA) and poly(2-hydroxyethyl methacrylate-co-sodium methacrylate) [P(HEMA-co-SMA)] hydrogels with different compositions were prepared to be used as intravaginal rings, and their gelation time, water content, mechanical properties and morphology were investigated. The water content of PHEMA and P(HEMA-co-SMA) hydrogels decreased as the concentration of the monomer and the degree of crosslinking increased, while the water content significantly increased as the content of SMA, the hydrophilic monomer, increased. The increasing of the concentration of the crosslinking agent affected the tensile and flexural properties highly. The presence of a proper small amount of SMA also led the tensile and flexural modulus to move to a higher level. The results showed that P(HEMA-co-SMA) hydrogel with high drug load and good mechanical properties at optimum preparation conditions can be prepared for intravaginal rings to deliver nonhormonal contraceptives. These results may be applied to prepare better intravaginal drug delivery devices.

Temperature control of multizone heated rollers

Heated press rollers are used to give tactility and gloss to papers, fabrics, nonwoven fabrics, films and so on. The surface temperature of the heated roller and its uniformity are especially important. Existing heated rollers have surface temperature profiles up to 10degC deviations, causing listing in fabrics. In order to suppress the surface temperature deviation to 1degC, we propose a heated roller system having multizone electric heaters and heating oil within the steel roller. The heated roller temperature control system is ill-conditioned. Because the controller performance is very sensitive on uncertainties in the model and disturbances, very accurate identification and elaborate controller design are required. For this, recent sequential relay feedback autotuning methods are applied for identification and controller design. Experimental results are given.

Solution polymerization behavior of acrylonitrile by moderate temperature azoinitiator

Abstract Acrylonitrile (AN) was solution-polymerized in dimethyl sulfoxide (DMSO) and tertiary butyl alcohol (TBA) at 30, 40 and 50°C using a moderate temperature initiator, 2,2′-azobis(2,4,-dimethylvaleronitrile) (ADMVN); the effects of type and amount of solvent, polymerization temperature, and initiator concentration were investigated. On the whole, the experimental results corresponded to predictions. Moderate polymerization temperature using ADMVN proved to be successful in obtaining polyacrylonitrile (PAN) of high molecular weight and high conversion with smaller temperature rise during polymerization. The polymerization rates of AN in DMSO and in TBA were proportional to the 0.61 and 0.94 powers of ADMVN concentration, respectively. For the same polymerization conditions, DMSO was slightly superior to TBA in increasing molecular weight of PAN. On the other hand, DMSO was inferior to TBA in causing conversion to polymer, indicating that the initiation rate of AN in DMSO was less than that in TBA. These effects could be explained by an activation energy difference. For PAN produced in DMSO at 30°C, weight-average molecular weight of 865,000 was obtained, with a polydispersity index of 1.89.

A method to determine iodine desorption of high molecular weight syndiotactic poly(vinyl alcohol)/iodine complex film

Abstract A method to calculate the iodine desorption of high molecular weight syndiotactic PVA (s-PVA)/iodine film in water was suggested, which was achieved by measuring the weight loss of s-PVA/iodine film and the solubility of s-PVA film after immersion in water. The degree of solubility of s-PVA film in water at 80°C was below 3% and the iodine desorption of s-PVA/iodine film at the same temperature was limited to below 13%, while atactic PVA film is completely soluble over 50°C. The desorption of iodines in water was strongly affected by the dissolution of PVA. The longer soaking time gave the larger desorption of iodine regardless of immersion temperature. The iodine desorption of s-PVA/iodine film in hot water decreased with increasing drawing temperature and draw ratio.

A zone drawing method to determine optimum polymer concentration and gelation temperature of high molecular weight polymer film

The zone drawing method has been used to determine optimum initial concentration and gelation/crystallization temperature for suitable macromolecular entanglements. Ultra-high molecular weight (UHMW) polyethylene (PE) gel films were prepared from decalin solution with different polymer concentrations and different gelation temperatures and then drawn under various zone drawing conditions. It was found that the initial concentration and gelation temperature of PE solution caused significant changes in draw ratio of UHMW PE gel film. That is, at initial concentration of 0.5 g/dl and at gelation temperature of 25°C, the one-step zone draw ratio revealed a maximum and gradually decreased at higher or lower concentrations. In addition, the lower the initial concentration, the lower the gelation/crystallization temperature. This tendency was similar to the maximum draw ratio data. Conclusively, it was identified that the optimum polymer concentration and gelation temperature of UHMW PE solution could be obtained simply by the zone draw ratio.