Tetsuo Kanamoto

Effects of crystalline forms on the deformation behaviour of nylon-6

Abstract Solid-state coextrusion draw was carried out for films of aggregates of solution- and melt-grown crystals of nylon-6 with α - and γ -forms. Under ordinal crystallization conditions, the crystal form was primarily a monoclinic α -form. Thus, α -crystals were converted to the γ -form by iodine treatment, followed by treatment with aqueous solution of sodium thiosulfate. The maximum extrusion draw ratio achieved (EDR max ) at temperatures in the range of 100–180°C was greatly affected by both the crystal forms and the initial morphologies. At a given crystal morphology, the EDR max for the γ -crystals was higher than the α -crystals. Further, the efficiency of draw evaluated from the crystalline chain orientation was higher for γ -crystals than α -crystals. For films with α -crystals, the intercrystalline network has an important role in transmitting the stress on draw. On the other hand, for films with γ -crystals, the effect of intercrystalline network on the efficiency of draw was less prominent. These results were almost independent of the extrusion temperature studied. The effect of crystal form on the ductility is explained based on the difference in the interchain interactions due to hydrogen bonding in the crystalline regions.

Elastic modulus and thermal conductivity of ultradrawn polyethylene

The axial and transverse Youngs modulus and thermal conductivity of gel and single crystal mat polyethylene with draw ratios λ = 1–350 have been measured from 160 to 360 K. The axial Youngs modulus increases sharply with increasing λ, whereas the transverse modulus shows a slight decrease. The thermal conductivity exhibits a similar behavior. At λ = 350, the axial Youngs modulus and thermal conductivity are, respectively, 20% and three times higher than those of steel. For this ultradrawn material both the magnitude and the temperature dependence of the axial Youngs modulus are close to those of polyethylene crystal. The high values of the axial Youngs modulus and thermal conductivity arise from the presence of a large percentage (∼85%) of long needle crystals.

Dynamic mechanical behavior of chitin and chitosan

Recently, much attention in the many fields has been paid to chitin(Poly-N-acetyl-D-glucosamine), which is formally considered an aminocellulose derivative that occurs widely in nature, for example, in the hard shell of insect and crustaceans, cuttlefish bone, and the cell walls of fungi, and its derivative, chitosan (Poly-D-glucosamine), which is readily obtained from chitin by N-deacetylation with alkali. However, there has been few papers concerning the physical properties of these polysaccharides. FUKADA et ai.(1975) examined the piezoelectricity of highly crystalline s-chitin, and found that a temperature dispersion appears only around -95~ which has been assigned to the water strongly bound to s-chitin. More recently, BRADLEY et ai.(1976) studied dynamic mechanical properties of some polysaccharides such as cellulose, amylose, and dextran containing various amount of water, and have characterized four mechanical transitions. In this paper, we report the effect of water on the dynamic mechanical properties of chitin and chitosan as a function of temperature.

Tensile properties of highly syndiotactic polypropylene

Abstract The tensile properties and uniaxial drawing of highly syndiotactic polypropylene (s-PP) have been studied. The results were compared to those of isotactic polypropylene (i-PP) having a comparable molecular weight, molecular-weight distribution and stereoregularity. S-PP and i-PP of different initial morphologies, prepared by crystallization from the melt and solution, were drawn by solid-state coextrusion and tensile drawing. The structure and properties of drawn films have been characterized by wide- and small-angle X-ray diffraction, stress-strain behaviour, etc. The maximum achievable draw ratio ( DR ) for s-PP was 5–10, depending on the initial morphologies, and significantly lower than that for i-PP ( DR ≤ 30). The poor ductility of s-PP was ascribed to the absence of a crystalline relaxation, which was clearly observed in the highly drawable i-PP by dynamic mechanical tests. The tensile properties of drawn films increased with DR for each of the PPs. At a given DR , however, the modulus was remarkably lower for s-PP than for i-PP, yet the tensile strengths were not significantly different. The maximum tensile modulus and strength of s-PP achieved in this work were 3.0 and 0.33 GPa, respectively. These values were remarkably lower than those (20 and 0.60 GPa, respectively) achieved for an i-PP having comparable molecular characteristics, reflecting the low crystal modulus, drawability and crystallinity of s-PP compared to those of i-PP. The structural change on drawing of s-PP was also discussed.

Elastic modulus of the crystalline regions of poly(ethylene-2,6-naphthalate)

Abstract Elastic modulus E 1 of the crystalline regions of poly(ethylene-2,6-naphthalate) (PEN-2,6) in the direction parallel to the chain axis was measured by X-ray diffraction. The E 1 (−4 1 1 0) plane of PEN-2,6 was 145 GPa at room temperature, which coincided with the calculated value (144 GPa) obtained by Treloars method. The E 1 value of PEN-2,6 is larger than that of poly(ethylene terephthalate) (observed, 108 GPa; calculated, 122 GPa). This difference could be attributed to the difference of the deformability between naphthalene and phenyl rings.

Property opportunities with polyolefins: a review. Preparations and applications of high stiffness and strength by uniaxial draw

Abstract Major progress has been made in preparation of high-modulus and high-strength fibres and films by uniaxial drawing of semicrystalline polyolefins. Solid-state coextrusion followed by tensile drawing on ultra-high molecular weight polyethylene (UHMWPE) and polypropylene (UHMWPP), and poly(4-methyl-1-pentene) starting from single-crystal mats, prepared from dilute solutions, produces superdrawn films with tensile moduli approaching the theoretical values reported for the crystal for each of these three polyolefins. For PE, a modulus of 220 GPa and strength of 6 GPa have been achieved. For PP, the corresponding maximum values are 37 and 2.2 GPa. This two-stage drawing technique has also been successfully applied for ultradrawing PE reactor powders. Films of compacted powder, prepared below the melting point of the powder, have been solid-state coextruded at 110°C to a draw ratio of 6, followed by tensile drawing at 120–135°C. The drawability and the uniformity of the resultant fibres and films are sensitively affected by the drawing temperatures and rates, and also by the choice of reactor powder. The maximum draw ratio achieved directly for reactor powder is ∼85, with a corresponding tensile modulus of ⩽ 130 GPa. For special conditions, high uniaxial draw and high modulus for selected reactor powders have been achieved simply by direct compaction plus calendering. In none of these processes is the polyolefin melting point exceeded. Applications of the oriented polyolefins are cited in terms of use as tapes, yarn and fabrics.

Enhanced electrical properties of highly oriented poly(vinylidene fluoride) films prepared by solid‐state coextrusion

Oriented poly(vinylidene fluoride) (PVDF) films with β-form crystals have been commonly prepared by cold drawing of a melt-quenched film consisting of α-form crystals. In this study, we have successfully produced highly oriented PVDF thin films (20 µm thick) with β-crystals and a high crystallinity (55–76%), by solid-state coextrusion of a gel film to eight times the original length at an established optimum extrusion temperature of 160°C, some 10°C below the melting temperature. The resultant drawn films had a highly oriented (orientation function fc = 0.993) fibrous structure, showing high mechanical properties of an extensional elastic modulus of 8.3 GPa and tensile strength of 0.84 GPa, along the draw direction. Such highly oriented and crystalline films exhibited excellent ferroelectric and piezoelectric properties. The square hysteresis loop was significantly sharper than that of a conventional sample. The sharp switching transient yielded the remnant polarization Pr of 90 mC/m2, and the electromechanical coupling factor kt was 0.24 at room temperature. These values are about 1.5 times greater than those of a conventional β-PVDF film. Thus, solid-state coextrusion near the melting point was found to be a useful technique for the preparation of highly oriented and highly crystalline β-PVDF films with superior mechanical and electrical properties. The morphology of the extrudate relevant to such properties is discussed.

Development of high ductility and tensile properties by a two‐stage draw of poly(acrylonitrile): Effect of molecular weight

Ultradrawing of atactic poly(acrylonitrile) (PAN) was investigated for a Mv series, ranging 8.0 × 104–2.3 × 106. Samples for the draw were prepared from 0.5–30 wt % solutions of PAN in N,N′-dimethylformamide. The solutions were converted to a gel by quenching from 100 to 0°C. The dried gel films were initially drawn uniaxially by solid-state coextrusion (first-stage draw) to an extrusion draw ratio (EDR) of 16, followed by further tensile draw at 100–250°C (second-stage draw). The maximum total draw ratio (DRt,max) and tensile properties achieved by two-stage draw increased remarkably with sample Mv. Other factors affecting ductility were the solution concentration from which gel was made and the second-stage draw temperature. The effects of these variables became more prominent with increasing Mv. The temperature for optimum second-stage draw increased with sample Mv. Both the initial gel and the drawn products showed no small-angle X-ray long period scattering maximum, suggesting the absence of a chain-folded lamellae structure, which had been found in our previous study on the drawing of nascent PAN powder. The chain orientation function (fc) and sample density (ρs) increased rapidly with DRt in the lower range (DRt 30–100. The tensile modulus also showed a similar increase with DRt. The tensile strength increased linearly with DRt, reaching a maximum, and decreased slightly at yet higher DRt. The highest modulus of 28.5 GPa and strength of 1.6 GPa were achieved with the highest Mv of 2.3 × 106.

Deformation mechanism of amorphous poly(ethylene terephthalate) as a function of molecular weight and entanglements

Abstract The deformation mechanism of amorphous poly(ethylene terephthalate)(PET) has been studied as a function of molecular weight and entanglement density in predrawn films. PET chips (intrinsic viscosity = 0.6–4.9 dl g–1) were dissolved in mixed solvent of 1,1,1,3,3,3-hexafluoro-2-propanol and dichloromethane. The polymer solutions (polymer conc. = 2–40 wt%) were frozen at −30°C and then most of the solvent was removed at −30°C under vacuum, resulting in amorphous films with various entanglement densities. The films were drawn by solid-state coextrusion at 70°C. It was found that the initial polymer concentration used for film preparation had a marked effect on the maximum achievable extrusion draw ratio (EDRmax) of the films, especially for higher molecular weights. The optimum concentration decreased and the highest EDRmax increased with increasing molecular weight. The deformability was also affected by the stress-induced crystals, which might act as net points. The tensile modulus and strength of drawn films were related to draw ratio and molecular weight. The higher the draw ratio and molecular weight, the higher were the tensile properties of drawn samples. The improved efficiency of draw with higher molecular weight was explained by the suppression of disentanglement and relaxation of oriented amorphous molecules during deformation; both are important in the development of structural anisotropy and continuity along the draw direction.

Lamellar thickening in nascent poly(acrylonitrile) upon annealing

No systematic study has been reported on the lamellar thickening in atactic poly(acrylonitrile) (PAN) upon annealing because PAN, in the form of solution-cast films or their drawn products, generally shows no small-angle X-ray scattering (SAXS) maximum corresponding to the lamellar thickness. In this work, PAN crystals were precipitated during the thermal polymerization of acrylonitrile in solution. The nascent PAN film, obtained by the filtration of the crystal suspension, exhibited a clear SAXS maximum revealing the lamellar structure. The lamellar thickening upon annealing of the nascent PAN films was studied in the temperature range 100–180 °C, where the degradation was minimal, as confirmed by the absence of an IR absorption band at 1605 cm−1 ascribed to the cyclized nitrile groups. Above 190 °C, the degradation of the samples was significant, and the SAXS became too broad to determine the scattering maximum. The long period was significantly affected by the annealing time (ta) and the temperature (Ta). Depending on ta, three stages were observed for the lamellar thickening behavior. The lamellar thickness stayed constant in stage I (ta = 0.5–3 min, depending on Ta), rapidly increased in stage II (ta = 0.5–8 min), and stayed at a constant value characteristic for each Ta at yet longer tas in stage III. The lamellar thickness characteristic for Ta increased rapidly with increasing Ta at 165 °C (or higher), which was 152 °C lower than the estimated melting temperature of PAN (Tm = 317 °C). A possible mechanism for such lamellar thickening in PAN far below the Tm is discussed on the basis of the enhanced chain mobility in the crystalline phase above the crystal/crystal reversible transition at 165–170 °C detected by differential scanning calorimetry and wide-angle X-ray diffraction. The structural changes associated with annealing are also discussed.