Strain Of Poly Research Articles

Processing and strain induced crystallization and reinforcement under strain of poly(1,4-cis-isoprene) from Ziegler–Natta catalysis, hevea brasiliensis, taraxacum kok-saghyz and partenium argentatum

Abstract Strain induced crystallization and reinforcement were studied for poly(isoprene)s from the following sources: Ziegler–Natta catalysis, hevea brasiliensis (HNR), taraxacum kok-saghyz (TKS), known as the russian dandelion, partenium argentatum (GR), known as guayule. Two HNR samples were studied, with high (HNR-H) and low (HNR-L) molar mass. Investigated guayule samples were: as isolated from the latex (GR-R) and after extraction with acetone (GR-P). All of the samples had weight average molar mass higher than 1.5 × 106 Da. TKS was found to be the most stereoregular sample, with undetectable amounts of stereoerrors. Wide angle X-Ray diffraction patterns were collected on samples, unstretched after processing and during stretching, up to 5 as the strain ratio. Quasi-static tensile measurements were performed. HNR and GR-P exhibited rubber crystallinity already in the undeformed state and the orientation of their crystalline phase remained low also for the highest strain ratios. GR-R and TKS were amorphous at low strain and developed highly oriented crystalline phases under stretching. TKS developed extraordinary mechanical reinforcement under stretching: stresses at large elongations were much higher than those obtained with HNR. It is thus shown that the formation of highly oriented crystalline phases brings large mechanical reinforcement. In conclusion, an amorphous NR sample from a natural source, such as TKS, which has high molar mass and does not contain non rubber components which could act as plastifiers, is able, under stretching, to develop crystallinity and a high degree of axial orientation. Crystallization occurs at high strain ratio, when the chains are prevailingly aligned. The biosynthesis of TKS is likely to play a strategic role, as it promotes the chain end crosslinking of the polymer chains.

Electrocaloric and electrostrictive effect of polar P(VDF–TrFE–CFE) terpolymers

The electrocaloric effect (ECE) is the adiabatic temperature change or isothermal entropy change caused by the polarization change of a dielectric material when subjected to a change of external electric field. The electrostrictive effect is a form of elastic deformation of a dielectric induced by an electric field, associated with those components of strain which are independent of reversal field direction. It was found that both the ECE, e.g., adiabatic temperature change, and the electrostrictive strain in poly(vinylidene fluoride–trifluoroethylene–chlorofluoroethylene) (P(VDF–TrFE–CFE)) terpolymers are proportional to the square of the electric field. The adiabatic temperature change ΔT of ECE versus electric field can be illustrated using a modified Belov–Goryaga equation. ΔT is proportional to E2 when E is small. For electrostrictive effect, the rigid-ion model assumes that the anharmonic movement of the ions leads to the quadratic strain–electric field relation. The quotient of electrostrictive coefficient Q over the phenomenological coefficient β is empirically a constant, indicating that the larger the electrostrictive coefficient, the larger the ECE, which opens a new way to find out new electrocaloric materials.

High poly(β-hydroxybutyrate) production by Pseudomonas fluorescens A2a5 from inexpensive substrates

A strain of poly(β-hydroxybutyrate) (PHB)-accumulating bacterium was isolated from the soil in Alaska of USA, identified as Pseudomonas fluorescens, and designated as strain A2a5. The organism grew at temperatures below 30 °C, and accumulated a large amount of granules in its cells when it was cultured in the sugarcane liquor medium. The purified sample from cells was determined as PHB by gas chromatographic and nuclear magnetic resonance analysis of polyesters. The cell density of the culture in shaking bottles reached OD 600 = 155 with PHB concentration of 31 g l −1. In 5 l bioreactor, a maximum cell dry weight (CDW) of 32 g l −1 with a PHB concentration of 22 g l −1 was obtained, and the PHB content was up to 70% and productivity was 0.23 g l −1 h −1.

Unusual thermal relaxation of viscosity-and-shear-induced strain in poly(ether-ketones) synthesized in highly viscous polyphosphoric acid/P2O5 medium

We recently described an improved method to synthesize poly(ether-ketones) or PEKs. It utilized an optimized mixture of polyphosphoric acid (PPA) and P2O5 that is not only milder, less corrosive and less expensive than super-acid media, but also can play the multiple roles of solvent, Friedel–Crafts catalyst and dehydrating agent. The as-prepared PEKs from such a highly viscous reaction medium displayed unexpected, thermally induced relaxation exotherms regardless of the amorphous or semi-crystalline nature of polymer. This thermal behavior was not observed for the formally identical polymers [viz. pPEK or poly(oxy-1,4-phenylenecarbonyl-1,4-phenylene] which is normally semi-crystalline) that were separately prepared in a much less viscous mixture of methanesulfonic acid and P2O5 (Eaton's reagent) or N-methyl-2-pyrrolidinone (NMP). Such an observation was first made when both samples of pPEKs were subjected to the same thermal history and the thermal relaxation exotherms were observed only for the pPEK sample that was prepared in PPA/P2O5 medium. Further confirmation of viscosity-and-shear-induced strain stored in the as-synthesized PEKs was provided by a systematic annealing study with differential scanning calorimetry (DSC), wide-angle X-ray diffraction (WAXD) analysis and Fourier-transform infrared spectroscopy (FT-IR). Based on these data, pPEK was successfully compression-molded in the temperature range of 230–250°C which is more than 100°C below its melting temperature.

Chain orientation resulting from the crystallization under strain of poly(ε‐caprolactone) in miscible blends with poly(styrene‐co‐maleic anhydride)

Chain orientation resulting from the crystallization under strain of poly(ε‐caprolactone) in miscible blends with poly(styrene‐co‐maleic anhydride)

Chain orientation resulting from the crystallization under strain of poly(ϵ‐caprolactone) in miscible blends with poly(styrene‐co‐maleic anhydride)

AbstractAmorphous miscible blends of poly(ϵ‐caprolactone) (PCL) with a random copolymer of styrene–maleic anhydride (SMA) were stretched at room temperature and the crystallization of PCL was allowed to develop under strain. The crystallization of PCL, from oriented amorphous chains, leads to macroscopic crystalline chain orientation. Using infrared dichroism and wide‐angle X‐ray scattering techniques, it was found that the resultant crystalline orientation of PCL is always parallel to the strain direction, regardless of the experimental conditions, which is in contrast with the PCL/poly(vinyl chloride) blend, where both parallel and perpendicular chain orientations can be induced. Furthermore, the degree of crystalline orientation of PCL is influenced by the initial stretching‐induced amorphous chain orientation of the system. © 2001 John Wiley & Sons, Inc. J Appl Polym Sci 81: 1683–1690, 2001

Differential Scanning Calorimetry of Stressed Polymers

Stresses which have been frozen into a polymer by cooling to below its glass transition temperature (Tg) are relieved when the polymer is reheated above its Tg. Polymers which have been elongated will contract above Tg. This sudden contraction just above Tg is detected as a sharp drop in the differential scanning calorimetric curve. This is the reverse of the well known superheating endotherm accompanying the expansion of annealed polymers. The decrease in the differential scanning calorimetric curve immediately after the Tg inflection can be quantitatively related to the residual strain in poly(vinyl chloride) and polycarbonate.

Experimental results relating stress and birefringence to strain in poly(dimethylsiloxane) networks. Comparisons with theory

Mesures en fonction de l'elongation pour deux polymeres differant par leur degre de reticulation. Les echantillons sont gonfles dans le dodecane, l'hexadecane, la decaline, le tetraethylmethane et le tetrachlorure de carbone. Relation entre la contrainte, l'elongation et la dilatation