The effect of polylactic acid (PLA)/poly‐d‐lactide stereocomplex on the thermal and mechanical properties of various PLA/rubber blends

This study investigated the effect of polylactic acid (PLA)/poly‐d ‐lactide (PDLA) stereocomplex (ST) on the improvement of the mechanical and thermal properties of various rubber‐toughened PLAs. In this work, natural rubber (NR), synthetic polyisoprene rubber (IR), silicone rubber (SI), acrylic rubber (ACM), acrylic core–shell rubber (CSR), thermoplastic copolyester (TPE) and thermoplastic polyurethane (TPU) were chosen as the toughening agents. 5 wt% PDLA was melt‐blended with PLA to form ST crystals in the presence of 15 wt% rubber in an internal mixer at 180 °C and 50 rpm. It was found that the melting temperature of ST crystal (T_m,sc) and the impact strength of ST/rubber blends were strongly correlated with the rubber domain size. For the blends of ST with compatible rubbers (ACM, CSR, TPE and TPU), the rubber domain sizes tended to be smaller with higher T_m,sc and higher impact strength than the blends with incompatible rubbers (NR, IR and SI). However, the presence of ST crystals in PLA/incompatible rubber blends, especially the blends with NR and IR, led to a significant increase in the rubber domain size and plunges in tensile toughness and impact strength. On the other hand, the presence of these crystals in PLA/compatible blends did not change the rubber size or the impact strength significantly compared with those without ST crystals except in the case of ST/ACM, which resulted in a large increase in the impact strength. Among all rubber types, CSR provided the highest impact strength for both the PLA and ST systems. © 2019 Society of Chemical Industry     

Eco-friendly high-performance coating for polyester fabric

Due to increasing environmental concerns and depletion of petroleum resources, the use of green materials has become popular with garment industry. In the past, natural rubber, which is one of the most prevalent bio-based elastomers, was used as waterproof coating for many applications due to its inherent elasticity, high tear and abrasion resistance, and hydrophobicity. However, NR has significant drawbacks when applying to garments including its poor adhesion to polyester fabrics and low breathability. Polyurethane, on the other hand, possesses high breathability but relatively poor elasticity. In this study, the fabric coating based on waterborne polyurethane and pre-vulcanized natural rubber latex was synthesized with the goal to produce fabric for high-performance applications, which could surpass criteria including water vapor permeability (WVP) (>10 000 g/m²•24hr), water pressure resistance (WPR) (>1000 mmH₂O), and stretchability (>300%). The best condition achieved when using 60NR cured for 15 min by using 1.5 phr sulfur could provide WPR value of 4090 mmH₂O and WVP of 11 033 g/m²•24hr. © 2019 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2019 , 136, 48002.     

Rheological investigation of cure kinetics and adhesive strength of polyurethane acrylate adhesive

In this work, we used rheological techniques to study both the cure characteristics and the degree of cure of polyurethane acrylate adhesive, a type of reactive adhesive used in hard disk component assembly. These results were then correlated with the tensile shear strengths of adhesives. Here, the cure characteristics of polyurethane adhesive were investigated at isothermal conditions ranging from 25 to 120°C. From the rheological results, the gelation time, the vitrification time, as well as the time required to reach the maximum degree of cure, decreased when increasing the curing temperature. The cure rates of adhesive increased with temperature in three temperature ranges, which were retardation zone, vitrification zone, and reaction‐controlled zone. The cure rates in these zones were controlled by slow diffusion, fast diffusion, and the rate of reaction, respectively. From the temperature sweep of fully‐cured adhesives, we found that the crosslinking level of adhesives increased with curing temperatures at different rates depending on the temperature zones as well. Moreover, the adhesive strength measured by tensile shear test was found to also increase correspondingly with the adhesives' T_g, indicating that the crosslinking level directly affected the adhesive strength. The strong dependence of adhesive strength with crosslinking level indicates that the crosslinking level was essential for high adhesive strength. The correlation of cure characteristics and adhesive strengths at various curing temperatures performed in this study can further provide useful information for planning appropriate curing schemes of polyurethane acrylate adhesives used in electronic and other industries. © 2011 Wiley Periodicals, Inc. J Appl Polym Sci, 2012     

Improvement in impact resistance of polylactic acid by masticated and compatibilized natural rubber

Mastication is the technique widely used to reduce viscosity of natural rubber and the higher mastication speed leads to lower NR viscosity. The optimum viscosity of NR that could provide high impact strength for the blends depends largely on the blending time and method. This study is focused on the enhancement of impact strength of polylactic acid (PLA) blended with masticated natural rubber (NR) using sorbitan ester (SE), a biodegradable food additive, as a compatibilizer. The effects of NR mastication, compatibilizer and NR contents and the mixture’s viscosity on the morphological, thermal and impact properties of PLA/NR blends were investigated in relation to the changes in the morphology, thermal properties and impact strength of PLA/NR blends. It was found that the optimum viscosity of NR that provided the highest impact strength to the blends was achieved when NR was masticated at 40 rpm for 15 min. The highest impact strength corresponded well not only with the small NR phase size, but also with the highest crystallization rate. For the effect of compatibilizer, it was found that a small amount of SE could more than double the impact strength of the blends, where the optimum compatibilizer content was 0.5 wt%. Interestingly, the high impact strength of the blends in all cases was accompanied by short interparticle distance and slightly higher percent crystallinity.     

The Influence of Solvent Properties and Functionality on the Electrospinnability of Polystyrene Nanofibers

Summary: In order to produce nanometer‐sized fibers at an industrial scale, not only the morphology but also the production rate of fibers is important. The effect of solvent properties and functionality on the production rate of electrospun PS nanofibers was investigated using eighteen different solvents. The solution concentration was varied between 10 and 30% w/v. Electrospinning of PS solutions was carried out at various applied voltages and tip‐to‐collector distances The production rate of the obtained PS nanofibers was quantified in terms of electrospinnability. We found that the chance for the resulting PS solution to be spinnable is greater for solvents with high dipole moment and low viscosity. The solvent that provided the highest electrospinnability for polystyrene was DMF and the functionalities that promoted high dipole moment and thus high spinnability were the carbonyl group and the nitrogen group with free electrons. General guidelines for choosing suitable solvents for successful production of electrospun nanofibers have also been proposed.

SEM image of PS 685D at 200× magnification and the %‐coverage of the fibers obtained by using DMF, chloroform, and 1,4‐dioxane.