Influence of the Solidification Process on the Mechanical Properties of Solid-State Drawn PCL/Sepiolite Nanocomposite Tapes

In this research, poly(ε-caprolactone) (PCL) was melt-mixed with sepiolite nanoclays in a twin-screw extruder. In a subsequent step, the extruded films were drawn in the solid state to highly oriented nanocomposite films or tapes. A twin-screw extruder equipped with a Sultzer mixer for improved mixing in combination with a bench top drawing unit was used to prepare oriented nanocomposite tapes of different sepiolite loading and draw ratios. In order to study the influence of the solidification step on the drawability of the materials, different cooling procedures were applied prior to drawing. Optical microscopy images showed that slow or fast solidification using different chill rolls settings (open or closed) for the cast films resulted in different morphological conditions for subsequent drawing. The addition of sepiolite nanofillers led to nucleation and faster crystallization kinetics and oriented tapes which deformed by homogenous deformation rather than necking. The addition of sepiolite significantly improved the mechanical properties of both undrawn and drawn PCL tapes and Young’s modulus (1.5 GPa) and tensile strength (360 MPa) for composites based on 4 wt% sepiolite were among the highest ever reported for PCL nanocomposites. Interestingly, samples cooled with open chill rolls (slow crystallization) showed the highest modulus while solidification with closed rolls (fast crystallization) showed the highest tensile strength after drawing.

Preparation of High Modulus Poly(Ethylene Terephthalate): Influence of Molecular Weight, Extrusion, and Drawing Parameters

Poly(ethylene terephthalate) (PET) which is one of the most commercially important polymers, has for many years been an interesting candidate for the production of high performance fibres and tapes. In current study, we focus on investigating the effects of the various processing variables on the mechanical properties of PET produced by a distinctive process of melt spinning and uniaxial two-stage solid-state drawing (SSD). These processing variables include screw rotation speed during extrusion, fibre take-up speed, molecular weight, draw-ratio, and drawing temperature. As-spun PET production using a single-screw extrusion process was first optimized to induce an optimal polymer microstructure for subsequent drawing processes. It was found that less crystallization which occurred during this process would lead to better drawability, higher draw-ratio, and mechanical properties in the subsequent SSD process. Then the effect of drawing temperature (DT) in uniaxial two-stage SSD process was studied to understand how DT (<Tg or close to Tg or close to Trec) would affect the crystallization, draw-ratio, and final mechanical properties of PET. The designed process in current work is simulated to an industrial production process for PET fibres; therefore, results and analysis in this paper have significant importance for industrial production.

Effect of the Control of Polymer Flow in the Vicinity of Spinning Nozzle on Mechanical Properties of Poly(ethylene terephthalate) Fibers

In the melt spinning of PET, effects of the variation of flow behavior in the vicinity of spinning nozzle on the mechanical properties of as-spun fibers and drawn fibers were investigated. The variation of flow behavior was introduced by the change of spinning nozzle diameter and by the irradiation of CO2 laser to the spin-line at a position immediately below the spinneret. The curve representing the correlation between strength and elongation at break of as-spun fibers shifted toward the upper-right direction by the applications of small diameter nozzle and laser irradiation, indicating that the toughness of as-spun fibers was improved. The two-stage continuous drawing of as-spun fibers with various draw ratios revealed that the correlation between strength and elongation of drawn fibers also shifted toward the upper-right direction by the application of small diameter nozzle and laser irradiation. In other words, improved toughness in the as-spun fibers was preserved in the drawn fibers. Accordingly, by the drawing of the as-spun fibers prepared by the combination of small-diameter nozzle and laser irradiation, high-strength and high-toughness PET fibers with the tensile strength of 1.68 GPa (12.1 cN/dtex) and the elongation at break of 9.1% was obtained. Numerical simulation of the melt spinning process incorporating the effects of nozzle diameter variation and laser irradiation heating indicated that the maximum Deborah number in the spin-line decreased by the applications of small diameter nozzle and laser irradiation heating. Accordingly, it was speculated that the variation of the state of molecular entanglement caused by the difference of polymer flow in the melt spinning process has significant effect on the mechanical properties of resultant fibers.

Distinct structural and optical regimes in natural silk spinning

This study investigates the relationship between birefringence and mechanical properties in the dragline silk of the gold orb weaving spider Nephila edulis. Using a custom birefringence-tensile testing device, we probed the orientation and water-induced swelling of fibers spun at variety of drawing rates ranging from 0.003 to 400 mm s(-1). Our results indicate that based upon drawing rate, silk fibers fall into three distinct regimes each with characteristic orientation and swelling properties. Further investigation using in situ tensile testing reveals interactions between a fiber's drawing speed, mechanical properties, and orientation that support previous model predictions. We propose that simultaneous birefringence-tensile testing provides a unique and readily accessible insight into the structural behavior of this interesting and important biomaterial.

Elasticity and photoelasticity relationships for polyethylene terephthalate fiber networks by molecular simulation

We present a framework for the development of elasticity and photoelasticity relationships for polyethylene terephthalate fiber networks, incorporating aspects of the primary molecular structure. Semicrystalline polymeric fiber networks are modeled as sequentially arranged crystalline and amorphous regions. Rotational isomeric states-Monte Carlo simulations of amorphous chains of up to 360 bonds (degree of polymerization, DP=60), confined between and bridging infinite impenetrable crystalline walls, have been characterized by Omega, the probability density of the intercrystal separation h, and Deltabeta, the polarizability anisotropy. ln Omega and Deltabeta have been modeled as functions of h, yielding the chain deformation relationships. The development has been extended to the fiber network to yield the photoelasticity relationships. We execute our framework by fitting to experimental stress-elongation data and employing the single fitted parameter to directly predict the birefringence-elongation behavior, without any further fitting. Incorporating the effect of strain-induced crystallization into the framework makes it physically more meaningful and yields accurate predictions of the birefringence-elongation behavior.