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Polylactic acid (PLA) is a well-known renewable and biodegradable polymer but is still limited by its low heat distortion temperature and brittleness. In this study, a PLA/flax composite containing flax fiber strands (5 wt%) was prepared through melt-compounding process followed by gamma irradiation at doses ranging from 0 to 20 kGy in the presence of a small amount of triallyl isocyanurate (TAIC) as cross-linking agent. The gel fraction of the composite was tested, and the datum showed that the gel fraction sharply increased first, and then slightly decreased with increasing irradiation dose. Gamma irradiation induced cross-linking of the polymer to form a three-dimensional network in the PLA/flax composite system. Irradiated composite could only swell instead of dissolving completely in chloroform, and the swollen morphology correlated with irradiation dose. The thermal stability of the PLA/flax composite was characterized using thermogravimetric analysis (TGA) temperature, and dimensional stability. Overall, irradiation modification improved the thermal resistance and dimensional stability of PLA composites. The mechanical property tests of the irradiated composites revealed increased tensile and impact strengths, reduced elongation-at-break, and unchanged tensile modulus. The analysis of water absorption of the composite demonstrated that the irradiation cross-linking induced no obvious effect on water absorption. Irradiation cross-linking modification cannot change the hydrophilicity or hydrophobicity of PLA composites. Overall, these findings look promising for future use in reinforcement and improvement of the thermal resistance of PLA/flax composites.

Crystallization of polylactic acid (PLA) has a profound effect on its thermal stability and mechanical properties. However, almost no crystallization occurs in actual injection molding process due to rapid cooling program. In this paper, flax fiber was employed as nucleator to enhance the crystallization capability of PLA. Effects of flax fiber content on cold crystallization, melt crystallization, crystallinity, crystal form, morphologies, and size of spherulites of PLA/flax fiber composites were investigated. Dynamic mechanical analysis was innovatively employed to study cold crystallization temperature of PLA/flax fiber composites under dynamic force, and the relationship between cold crystallization temperature (y) and flax fiber content (x) data was fitted by the function y = 34.1 × exp (−x/5.7) + 78.0. The differential scanning calorimetry results showed that the cold crystallization temperature of composites dropped, the melt crystallization temperature of composites increased, and the crystallinity of composites improved with increasing of flax fiber content. Using polarized optical microscopy, it has been found that the spherocrystal size of composites was much smaller than that of neat PLA, and flax fiber induced transcrystallization on the flax fiber surfaces. Wide-angle X-ray diffraction was applied to reveal that flax fiber significantly enhanced the formation of α-form PLA crystals.

Fiber–matrix interaction plays a key role in the development of high-performance polymer/fiber composites. Flax fiber surface was modified by alkali treatment, corona discharge, maleic anhydride (MA) grafting and aminopropyltriethoxysilane treatment. Chemical structure of the treated fibers was characterized by FTIR, and the results revealed that alkali treatment removed hemicelluloses, lignin, waxes and oils. In addition, MA and silane reacted with the fiber to form –OCO–CH=CH–COOH and –(CH2)3–NH2 groups. Oil/water test was carried out on the treated fiber, and the results indicated that MA grafting and silane treatment changed the wettability of fiber from hydrophilic to hydrophobic. The morphology of fibers was observed by scanning electron microscope (SEM). It was obvious that the surface of alkali-treated fiber was very rough, and the surface of MA-grafted fiber and silane-treated fiber was covered by a coating layer. High toughness polylactic acid (PLA)/flax composites were fabricated by blending the modified fibers with PLA. The mechanical properties of PLA/flax composites were evaluated. The results showed that the impact strength and elongation-at-break of PLA/treated fiber composites were higher than those of PLA/untreated fiber composites. The compatibilizing mechanism between the fibers and PLA was discussed according to experimental phenomena and their corresponding results. Alkali treatment led to a rougher fiber surface, and formed more contacting points to enhance mechanical interlocking between PLA and fiber. The –OCO–CH=CH–COOH group of MA-grafted fiber and the –(CH2)3–NH2 group of silane-treated fiber acted as adhesive agents to hook the fiber to the matrix, and increased the fiber–matrix interaction.

It is difficult for polyethylene terephthalate (PET) to degrade, which caused severe pollution. In this work, polylactic acid (PLA) was introduced to improve the degradation of PET. PET/PLA was synthesized by extrusion blending. The thermal, crystalline and mechanical properties of blends were investigated with TGA, DSC, WAXD and universal testing machine. The degradation of the blends in soil, acid and alkaline buffer solutions was assessed, respectively. It was found that the introduction of a little PLA promoted crystallization of PET during injection molding process. The starting decomposition temperature lowered from 412.1 °C of pure PET to 330.4 °C at 50% PLA content, tensile and bending strength of blends gradually decreased with the PLA content increasing, while the degradation rate improved. Alkaline environment was most beneficial for blends to degrade. The degradation mechanism was discussed.

Poly (lactic acid) (PLA) is a renewable and biodegradable polymer with high modulus, high strength but low toughness. Blending PLA with plant fiber has been believed an available strategy to improve the toughness of PLA. PLA/Flax composites were fabricated by extrusion and injection molding processes. The flax fiber surfaces were modified before blending to improve the compatibility, and the chemical structures of both untreated and treated fiber were characterized by Fourier transform infrared spectroscopy. Results of mechanical test showed that the impact strength and elongation at break of PLA/Flax composites were remarkably higher than PLA. The impact fractures of PLA/Flax composites were also observed by scanning electron microscope. The results showed uniform dispersion of fibers in PLA matrix and good compatibility between treated fibers and PLA matrix. Moreover, it can be observed that crazing propagation was hindered by fibers and transcrystalline developed along fibers by polarized optical microscope. Differential scanning calorimetry analysis was carried out to study the crystallinity of PLA and it was found that incorporation of fiber improved the crystallinity of PLA. The toughening mechanism of PLA/Flax composites was discussed according to the results. © 2015 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2015, 132, 42573.

A simple approach for preparing electrospun poly(ethylene terephthalate) (PET) fibrous membranes with excellent spinnability and mechanical properties is introduced in this article. To enhance the electrospinnability of PET, a small content of ethanol was incorporated into a 16 wt % PET solution. The effects of ethanol on the solution properties, mechanical properties and crystallization properties and the related morphology were systematically evaluated. The conductivity (κ) measurement indicated that ethanol could obviously improve κ of the PET solution; this correlated well with the morphology of fibers. Scanning electron microscopy images showed that the diameter of the fibers decreased with increasing solution κ. The tensile strength of the PET fibrous membrane increased 1.8 times through the blending of 2.5 vol % ethanol with the PET solution. The differential scanning calorimetry results showed that the crystallinity was improved when the ethanol content increased; this was beneficial to the enhancement of the tensile strength. The glass-transition temperature and melting temperature increased slightly, but the cold-crystallization peak shifted to a lower temperature with increasing ethanol content (