Surface wetting phenomena of plasma polymer-coated sheets of poly(l-lactic acid)/poly(butylene succinate)

Water-repellent surfaces were fabricated on blend sheets of poly(l-lactic acid)/poly(butylene succinate) with various blending ratios by the successive processing; (1) plasma etching, followed by (2) the hydrophobic plasma polymer coating. Rough morphology was formed effectively on the mosaic structured surface of blend sheets via the oxidative etching, and advanced water repellency was achieved after the thin membrane coating was synthesized with a hydrophobic plasma polymer coating by use of hexamethyldisiloxane or hexamethyldisilazane. High water repellency is expressed through the columnar hair-like structured model, where the air-water surface interaction in the voids is taken into account.     

Fabrication of high conductivity dual multi-porous poly (l-lactic acid)/polypyrrole composite micro/nanofiber film

Dual multi-porous PLLA (poly(l-lactic acid))/H₂SO₄-doped PPy (polypyrrole) composite micro/nano fiber films were fabricated by combining electrospinning with in situ polymerization. The morphologies and structures of the resulting samples were analyzed by scanning electron microscopy (SEM). It was found that the composite micro/nano fibers exhibited a core-shell structure and the composite fiber film had a dual multi-pore structure composed of pores both in the fibers and among the fibers. Semiconductor parameter analyzer was used to characterize the electrical properties of the samples. It was interesting to find that all the PLLA/H₂SO₄-doped PPy composite micro/nano fiber films had higher conductivity than H₂SO₄-doped PPy particles when the polymerization time up to 180 min. Effects of the pyrrole synthesis conditions on the pore size and the conductivity of PLLA/PPy composite fiber film were assessed. By optimizing the polymerization conditions, the max conductivity of this composite fiber film was about 179.0 S cm⁻¹ with a pore size of about 250 μm. The possible mechanism of PLLA/H₂SO₄-doped PPy composite micro/nano fiber films had much higher conductivity than H₂SO₄-doped PPy particles was discussed.     

Coating of collagen on a poly(l-lactic acid) sponge surface for tissue engineering

Porous scaffolds play important roles in tissue engineering. Biodegradable synthetic polymers, such as poly(l-lactic acid) (PLLA), frequently are used in the preparation of porous scaffolds. Pretreating the surface of a PLLA porous scaffold is required to increase its wettability for smooth cell seeding due to the hydrophobic property of the scaffold's surface. In this study, a simple coating method was used to modify the surface of the PLLA sponges. The coating method included three steps: filling the PLLA sponge pores with collagen aqueous solution, centrifuging to remove excess collagen, and, finally, freeze-drying. Compared with the uncoated PLLA sponge, the collagen-coated PLLA sponge demonstrated both improved wettability and high water absorption. Cells were smoothly seeded in the collagen-coated PLLA sponges by dropping a cell suspension solution onto the sponges. Cells adhered to the collagen-coated sponge and were distributed homogeneously throughout the collagen-coated PLLA sponge.     

Nucleation and crystal growth kinetics of poly(l-lactic acid) with self-assembled DBS nanofibrils

The effect of 1,3:2,4-dibenzylidene-d-sorbitol (DBS) on the crystallization behaviors of poly(l-lactic acid) (PLLA) was examined in this study. A small amount (≤4 wt%) of DBS altered the crystallization rate and regime transition temperature of PLLA. First, the addition of DBS and the formation of self-assembled DBS nanofibrils both increased the nucleation rate of PLLA. Second, the curves of the spherulitic growth rate versus the crystallization temperature of PLLA were discontinuous and did not show the typical bell-shaped behavior for all samples. We found that the change in crystal structures (α′-to-α) affected the regime transition temperatures, which led to the discontinuity. The regime transition (regime II–III) temperatures of PLLA slightly decreased as the DBS amounts were increased. This indicates that the more regular structure (regime II) of PLLA formed at lower temperatures when more DBS was added. In addition, the spherulitic growth rate of PLLA was found to be mainly influenced by the fold surface free energy. When the DBS amounts were increased, the increase in the fold surface free energy decreased the growth rate of PLLA. Nonetheless, the Avrami exponent, n, was not significantly changed because the spherulitic growth geometry and nucleation mechanism of PLLA were basically the same. The Avrami plot also shows that the secondary crystallization began earlier due to the formation of DBS nanofibrils for the samples containing higher DBS amounts.     

Oriented morphology and enhanced mechanical properties of poly(l-lactic acid) from shear controlled orientation in injection molding

This study investigates the effect of operative parameters of shear controlled orientation in injection molding (SCORIM) on poly(l-lactic acid), PLLA, and compared with conventional injection molded (CIM) PLLA. The in situ structure development was carried out with systematic variations of mold temperature and shearing time. The energy at break and maximum stress of all the SCORIM processed PLLA are higher than the CIM processed PLLA without sacrificing the modulus. The overall increments in maximum stress and energy at break were 134% and 641%, respectively. Significant enhancements in ductility for the SCORIM processed PLLA are shown to be a consequence of preferential molecular orientation of large fraction of core. The orientation of core is more pronounced at low mold temperature conditions and was increased with increasing shearing time at both the low and high mold temperatures. The processing–morphology and morphology–mechanical property relationships were then established.     

Fabrication and degradation of poly(l-lactic acid) scaffolds with wool keratin

As a natural protein, wool keratin was used to improve the cell affinity of poly(l-lactic acid) (PLLA). Small keratin particles were prepared from keratin solution by the spray-drying process. Keratin particles were blended with PLLA/1,4-dioxane solution and paraffin micro-spheres which were used as progens. After the mixture was molded and dried, the paraffin micro-spheres were removed by cyclohexane. PLLA/keratin scaffolds with controlled pore size and well interconnectivity were fabricated. Keratin releasing rate was detected by Fourier transform infrared (FTIR) after the scaffold was immersed into PBS up to 4 weeks. The surface chemical structure was examined by X-ray photoelectron spectroscope (XPS). The results suggested that the keratin could be held into the scaffold which was expected to improve the interactions between osteoblasts and the polymeric scaffolds.     

In vitro hydrolytic degradation of poly(para-dioxanone)/poly(d,l-lactide) blends

A series of biodegradable polymers were prepared by solution coprecipitation of poly(para-dioxanone) (PPDO) and poly(d,l-lactide) (PDLLA) in various blend ratios. Samples were compression molded into bars using a platen vulcanizing press. The in vitro hydrolytic degradation of PPDO/PDLLA blends was studied by examining the changes in weight, water absorption, tensile strength, breaking elongation, thermal properties, and morphology of the blends in phosphate buffered saline (PBS; pH 7.44) at 37 °C for 8 weeks. During the hydrolytic degradation, the weight loss and water absorption increased significantly for all samples, whereas the hydrolysis rate varied with the blend composition. The weight loss of PPDO/PDLLA 80/20, which showed the smallest degradation rate, was lower than that of pure PPDO for almost all of the hydrolytic degradation period. The results showed that the blend composition played an important role in determining the degradation behaviors of blends.     

X-ray diffraction studies on stress transfer of kenaf reinforced poly(l-lactic acid) composite

Mechanical reinforcement of environmentally friendly composite, composed of kenaf fibers as reinforcement and poly-l-lactic acid (PLLA) resin as matrix, was investigated. The stress on the incorporated fibers in the composite under transverse load was monitored in situ and non-destructively using X-ray diffraction. The outer applied stress was found to be well transferred to the incorporated kenaf fibers through the PLLA matrix, which suggests a strong interaction between the fiber and the matrix. In addition, it was also revealed that a silane-coupling treatment to the kenaf fiber was effective for the improvement of interfacial adhesion.     

Heat and compression molded electrospun poly(l-lactide) membranes: Preparation and characterization

The fibrous membranes prepared by electrospinning have great advantages, such as high porosity and high specific surface area. However, low mechanical strength of electrospun membranes has been one of the most difficult technical problems to overcome, resulting in negative impact on the application. In this paper, the heat-assisted compression approach was employed to improve the mechanical performances of electrospun poly(l-lactide)(PLLA) membranes, especially in tensile strength. It is found that the electrospun PLLA membranes crystallize in α form and strong fiber-to-fiber linkages occurred with the aid of heat and compression. The tensile properties including tensile strength and modulus of membranes treated with a press at 6 MPa and a temperature at 60 °C (80 °C and 100 °C) increased by more than 100% compared with those of the as-electrospun membranes.     

Influence of fiber surface-treatment on interfacial property of poly(l-lactic acid)/ramie fabric biocomposites under UV-irradiation hydrothermal aging

The present study is devoted to the effect of fiber surface-treatment on the interfacial property of biocomposites based on poly(l-lactic acid) (PLLA) and ramie fabric. Ramie fiber is used as reinforced material because it's lowest water absorption among sisal, jute, kenaf and ramie fiber. Fiber surface-treatment can increase the water absorption of natural fibers. SEM images show that PLLA biocomposites with treated ramie fabric exhibit better interfacial adhesion character. DMA results show that the storage modulus of PLLA biocomposites with treated ramie increase compared to neat PLLA and PLLA biocomposites with untreated ramie. Unexpectedly, fiber surface-treatment can cause an accelerated decline in mechanical properties of PLLA biocomposites after UV-irradiation hydrothermal aging. Finally, GPC results show that there is no obvious decline in the molecular weight of PLLA. The main reason for this decline is the interfacial destructive effect induced by the water absorption of ramie fiber.