Recently, various fine cellulose fibers (CFs) such as cellulose nanofiber and microfibrillated cellulose have been developed. However, it is not clear how the addition of these fine CFs influences the physical properties and structure of paper. This study examines the benefits of adding fine CFs, including nano- and submicron-sized CFs, to paper by mixing them into unbeaten pulp, and discusses CF size differences between the micron and smaller scales. Two types of CFs were used in this study. One consists of micro-, submicron-, and nano-sized CFs (CF1) and another consists of nano- and submicron-sized CFs (CF2). The results show that both CF1 and CF2 enhance the tensile index, stretch at break, and tensile energy absorption of a handsheet. To explain these results, the fiber strength index and bond strength index were calculated using the Page's equation, and the tensile index for the handsheets with CF1 and CF2 showed a strong correlation with the bond strength index, thus suggesting that CF1 and CF2 were deposited in locations where there was interfiber bonding. However, differences were observed in the internal structures of the paper samples, indicating that CF2 did not change the pore volume and pore size of the resulting samples.
A commercially available carbonate oligomer, poly(hexamethylene/ pentamethylene carbonate) (PHPC), was found to involve various minor units that had been formed during the ester-exchanging polycondensation of ethylene carbonate and a mixture of 1,6-hexanediol and 1,5-pentanediol. This PHPC oligomer was chain-extended by using diphenyl carbonate as chain extender and then subjected to tin-catalyzed ring-opening polymerization of L-lactide to prepare ABA tri-block copolymers consisting of poly-L-lactide (PLLA) and PHPC as the hard A and soft B blocks, respectively. With the chain-extended PHPC as the macro-initiators, the molecular weights of the resultant copolymers became significantly higher even at increased contents of PHPC. The tri-block copolymers obtained were fabricated into polymer films by solution casting, and their properties were analyzed. It was revealed that the tri-block copolymers PLLA-PHPC-PLLA can be novel thermoplastic elastomers that are environmentally friendly in terms of utilization of carbon dioxide as feedstock.
This article concerns surface roughness of PBO fibers. Atomic force microscopy is applied to measuring the surface roughness of the PBO AS, HM and HM+ fibers. Also linear thermal expansion was measured. The reason that the surface roughness is decreased as fiber modulus increases is discussed from the viewpoint of microscopic fiber surface structure. There is a discussion in that the smoothness of fiber surface has relation with fiber modulus, molecular orientation and crystallinity of the fibers. The coefficient of thermal expansion is also measured. The PBO HM+ fiber shows a lower value (-8.7 × 10-6 K-1) of coefficient of thermal expansion than that of the PBO HM.
Permanent waving is important process to set hair configuration for the maintenance of wanted hairstyle. This process consists of scission of disulfide (SS) cross-links in hair keratin by reduction, washing with water to remove reductants, and subsequent reformation by oxidation. It is important to assess the type, number and location of SS cross-links to understand setting mechanism which has been still unknown. Even though the reduction of SS bonds with thiol is equilibrium reaction, there are few researches focusing on washing step which may decrease drastically the concentration of reductants inside or on the surface of the hair fiber. In a permanent waving system consisting of three step processes of reduction with thioglycolic acid (TGA), washing with water and oxidation by sodium bromate, we attempted to quantify the amount of reformation of SS cross-links during washing, and clarify the effect of washing time on the reproduction of the SS cross-links in microstructures of hair. In order to estimate the change in the cross-link density of hair, the force-extension curve for rubber-like swollen hair fibers treated in a specific diluents mixture was analyzed by using a rubber elasticity theory derived from a two-phase model comprising of the globular matrix of keratin-associated proteins (KAP) dispersed in a swollen network of the intermediate filament (IF) proteins. It was found that the integrity of the SS cross-linked structure of IF is retained, while the intermolecular SS cross-links between KAP molecules cleaved by the reduction are regenerated by the reverse reaction of the equilibrium reactions occurring during washing, and this leads to increase of the extension modulus and breaking stress of the hair fibers in water.