Masaoki Takahashi

Characterization of chemical and solid state structures of acylated chitosans

Abstract A series of acylated chitosans were synthesized by reacting chitosan with hexanoyl, decanoyl, and lauroyl chlorides. The chemical structures of these polymers were characterized by elemental analysis, IR, 1H-NMR, 13C-NMR, and GPC. These results suggested that the degree of substitution was 4 per monosaccharide ring. These acylated chitosans exhibited an excellent solubility in organic solvents such as chloroform, benzene, pyridine, and THF and transparent films were obtained from these solutions. Dynamic mechanical analyses (DMA) showed that all acylated chitosans have two phase transitions in the solid state. The first transition at −10, −42, and −40°C are attributable to the glass transition (Tg) of H-, D-, and L-chitosans, respectively. The second one around 88°C may be attributed to the transition related to the structure formed by the side chains. WAXS analyses indicate that these polymers form a layered structure in solid state and the layer spacing d increases linearly with increasing the length of side chains.

Observation of deformation and recovery of poly(isobutylene) droplet in a poly(isobutylene)/poly(dimethyl siloxane) blend after application of step shear strain

The deformation and recovery of a poly(isobutylene) droplet with a lower viscosity embedded in a poly(dimethyl siloxane) matrix are directly observed from two directions after application of a large step shear strain. The droplet shape and recovery time strongly depended on the magnitude of the applied strain. Just after application of a large strain, a droplet deforms almost affinely to a flat ellipsoid. It then changes into a rodlike shape, a dumbbell, and to an ellipsoid of revolution, and finally to a sphere. Model calculations show that the primary driving force for the shape recovery is the interfacial energy in order to reduce the surface area of the deformed droplet.

Quantitative assessment of strain hardening of low-density polyethylene melts by the molecular stress function model

The elongational viscosity of three tubular and five autoclave low-density polyethylene (LDPE) melts is analyzed, and quantitative comparison of the strain-hardening characteristics is made by using the molecular stress function model. This is based on a new strain-energy function, which assumes that the total strain energy of a branched section of a macromolecule is given by the addition of the strain energies of the individual chain segments contained in this section. The model employs only two nonlinear material parameters: one parameter describes the average number of crosslinked chain segments, which occupy the same tube section, and determines the slope of the elongational viscosity after inception of strain hardening. The second parameter indicates the maximum relative stretch of the chain segments and determines the steady-state (plateau) value of the elongational viscosity. Both parameters depend on the complex branching topology of LDPE melts. While quantitative relationships between branching structure and the two nonlinear parameters are not yet available, the results of this comparison seem to indicate that the more tree-like structure of autoclave LDPE leads to a higher density of crosslinked chain segments in the same tube section than in the case of LDPE polymerized in tubular reactors.

Structure and properties of MVS yarns in comparison with ring yarns and open-end rotor spun yarns

The structure and properties of Murata vortex spun yarns are investigated and compared with ring and open-end rotor spun yarns. Cotton yarns are spun from the same lot of Australian raw cotton fibers using the Murata vortex, ring, and open-end rotor spinning methods. Yarn structures are observed with an optical microscope equipped with a digital camera. Based on the digitized photographs, fiber arrangements are classified as wild, wrapper-wild, wrapper, belly-band. and core. Yarn diameter, yarn helix angle, wrapper fiber pitch, wrapper fiber crest, wrapper fiber length for a one-turn twist, and wrapper fiber helix angle to the yarn axis are examined, and yarn parameters such as tenacity, evenness, and hairiness are evaluated. The mechanical properties of dry relaxed yarns are measured with Kawabata Evaluation System instruments. Attempts are made to relate yarn structure differences to differences in the yarn formation mechanism for the three spinning meth ods. The differences in measured yarn properties such as evenness, hairiness, bulkiness. tenacity, compression properties, and bending properties can be explained by the observed differences in the yarn structure.

Poly(D-lactic acid) as a rheological modifier of poly(L-lactic acid): Shear and biaxial extensional flow behavior

The effect of addition of a small amount of poly(D-lactic acid) (PDLA) on the melt rheology of poly(L-lactic acid) (PLLA) was investigated. PDLA added to PLLA produces a stereocomplex which stays unmelted even above Tm of PLLA. Because of the imbalanced contents of component polymers, the stereocomplex does not grow into a large crystallite but rather acts as a crosslinking point of PLLA chains resulting in the apparent introduction of the long chain branching as well as in the apparent increase in molecular weight. Such changes in the molecular structure give rise to the change in the melt rheology depending on the content and the molecular weight of PDLA. The addition of low Mw PDLA significantly affects the shear rheology of PLLA melts while high Mw PDLA does not give such a significant effect. However, the addition of PDLA with high and low Mw’s gives a strong strain hardening character to PLLA melt even at a very low PDLA content.

Shape recovery of a dispersed droplet phase and stress relaxation after application of step shear strains in a polystyrene/polycarbonate blend melt

We observed the stress relaxation and shape recovery of a dispersed droplet phase after application of step shear strains in a polystyrene/polycarbonate blend melt. A polystyrene makes a droplet phase in a polycarbonate matrix of higher viscosity. The orientation angle of the droplet is independent of the initial radius. The angle does not change during stress relaxation and is nearly equal to the angle given by the affine deformation. The shape recovery of the droplets leads to the decay of the relaxation modulus at long times. The stress relaxation slows down at long times for large strains, reflecting the retarded shape recovery of the droplets. Calculated time dependences of the relaxation modulus based on the rate equations by Doi and Ohta [J. Chem. Phys. 95, 1242–1248 (1991)] do not agree with the observed slowing down of the stress relaxation. A force balance equation developed by Cohen and Carriere [Rheol. Acta 28, 223–232 (1989)] explains the retarded shape recovery of the droplet from a prolonged ellipsoid of revolution to a sphere.We observed the stress relaxation and shape recovery of a dispersed droplet phase after application of step shear strains in a polystyrene/polycarbonate blend melt. A polystyrene makes a droplet phase in a polycarbonate matrix of higher viscosity. The orientation angle of the droplet is independent of the initial radius. The angle does not change during stress relaxation and is nearly equal to the angle given by the affine deformation. The shape recovery of the droplets leads to the decay of the relaxation modulus at long times. The stress relaxation slows down at long times for large strains, reflecting the retarded shape recovery of the droplets. Calculated time dependences of the relaxation modulus based on the rate equations by Doi and Ohta [J. Chem. Phys. 95, 1242–1248 (1991)] do not agree with the observed slowing down of the stress relaxation. A force balance equation developed by Cohen and Carriere [Rheol. Acta 28, 223–232 (1989)] explains the retarded shape recovery of the droplet from a prolonge...

Rheological properties of low-density polyethylenes produced by tubular and vessel processes

Abstract Various rheological properties have been studied for two kinds of low-density polyethylenes (LDPEs): one is produced by tubular process (tubular LDPE) and the other by vessel process (vessel LDPE). The latter shows smaller g ′-parameter, the ratio of intrinsic viscosity to that of linear polyethylene. It was found that both LDPEs exhibit marked strain hardening behavior, i.e. upturn departure from the low strain rate asymptote, in both uniaxial and biaxial elongational viscosities, with stronger strain hardening in uniaxial elongation. Further, the vessel LDPE exhibits larger upturn behavior than the tubular LDPE. In the stress relaxation measurement, the vessel LDPE shows larger damping function, while the tubular LDPE shows values similar to those predicted by the Doi–Edwards theory. Furthermore, there is a significant difference in the effect of the shear history on the melt strength. The melt strength of the vessel LDPE decreases more rapidly with the shear history than that of the tubular LDPE. All these differences between the two types of LDPEs are due to the difference in the branch structure. The complex, multi-branched structure of the vessel LDPE gives much more prominent elastic features.

Dynamic interfacial properties of polymer blends under large step strains: shape recovery of a single droplet

We observed shape recovery of a deformed droplet in an immiscible polymer matrix under large step strains using stereo microscopes from two directions. On application of a large step strain, a soft spherical droplet in a matrix with higher viscosity deformed to a flat ellipsoid. The stretch ratio of major axis of the flat ellipsoid was 5/4 times larger than that predicted from the affine deformation. The flat ellipsoid changed into a rod-like shape and then to a dumbbell, to an ellipsoid of revolution, and finally back to the sphere. The orientation angle between the major axis and shear direction did not change during the course of this shape recovery and was independent of the initial radius of the droplet. The time needed for the whole shape recovery got longer as the initial radius and the strain were increased. For a given step strain, the normalized interfacial area plotted against the stretch ratio fell onto a master curve irrespective of the initial radius of the undeformed droplet. It is shown that the deformed droplet reforms to the sphere after it passes through various shapes by reducing the interfacial area.

Bulk properties of multibranched polystyrenes from polystyrene macromonomers : rheological behavior I

Abstract Dynamic shear moduli of multibranched polystyrenes were measured as functions of frequency and temperature using a parallel-plate rheometer. The multibranched polystyrenes are poly(macromonomer)s of ω-methacryloyloxyethyl polystyrene macromonomers (MA-PSt)s and statistical copolymers of the MA-PSt with methyl methacrylate (MMA) monomer. The master curve of the storage dynamic shear modulus G′ for the poly(macromonomer)s did not show the so-called plateau region and the G′ gradually decreased from the edge of the glass transition region to the terminal zone and the loss modulus G″ was always larger than G′. The plateau region became clear in the copolymers with less branch density. These results indicate that the intermolecular chain entanglement might be strongly restricted in the poly(macromonomer) systems due to the multibranched structure of high branch density, which also explains the brittle property of the poly(macromonomer) films.

Effects of Laundering on the Surface Properties and Dimensional Stability of Plain Knitted Fabrics

The effects of laundering and laundering temperatures on surface properties and dimensional stability are investigated for plain flat knit silk, cotton, and polyester fabrics with varying cover factors. The fabrics are subjected to relaxation processes and an extended series of wash and tumble-dry cycles in laundering baths of various tempera tures. Dimensions, surface friction, and roughness of the fabrics are measured in every process. Changes in dimensional stability and surface properties with relaxation processes and laundering temperatures are clarified. Relations between frictional motion and struc tural parameters are also discussed. The results reveal that the dimensional stability of silk is sensitive to a particular temperature. The highest shrinkage is recorded with slackly knitted cotton at the highest temperature. There is a considerable effect of wet relaxation on dimensional stability as well as surface properties. Silks coefficient of friction is the highest, and the lowest surface friction for cotton occurs at the highest temperature. Slackly knitted fabrics also show higher friction than tightly knitted fabrics. The coeffi cient of friction has a tendency to decrease with increasing tightness, while the surface roughness shows an opposite tendency. There is a good correlation between stick-slip motion and ribs on the fabrics.