| Poly(lactic acid)(PLA) is a kind of thermoplastic aliphatic polyester that boasts a good clarity, biodegradability, biocompatibility and high mechanical strength etc. PLA is considered as the most promising material to replace for petroleum-based polymers. However, the application of PLA is restricted due to its low crystallization rate, low deformation temperature, brittleness and flammability etc. Ionic liquids (ILs) are "green" molten salts that consist of anion and cation. As novel solvents and functional additives, ILs have received some increasing attentions in polymer research and application fields recently, due to its novel features, such as low vapor pressure, high flame retardancy, excellent solubility and plasticized effect, and so on.Three different imidazolium-based ILs were blended with PLA to prepare ILs/PLA blends. Tensile property, thermal stability, melt fluidity, crystallization behavior, morphological structure and flame retardant property of these blends were studied. These selected ILs were1-pentyl-3-methylimidazolium tetrafluoroborate ([PtMIM]BF4),1-ethoxyethyl-3-methylimidazolium tetrafluoroborate ([EOEIM]BF4) and1-butyl-3-methylimidazolium dibutylphosphate (BMIM(C4H9O)2PO2), respectively.The main researching contents followed as:1. The effects of [PtMIM]BF4and [EOEIM]BF4on tensile property of PLA were studied, respectively. Tensile test results demonstrate that both the ILs can improve the toughness of PLA. Elongation at breaking of PLA blends increases with the increase of ILs contents, and then decreases modestly. Comparatively speaking,[PtMIM]BF4/PLA blends have better toughness compared to [EOEIM]BF4/PLA blends. The elongation at breaking of [EOEIM]BF4/PLA blend reaches to the maximum value of38%with the incorporation of4phr [EOEIM]BF4. For [PtMIM]BF4/PLA blends, the elongation at break reach to the maximum value of53.5%with the addition of6phr [PtMIM]BF4. On the one hand,[PtMIM]BF4shows a better compatibility with PLA matrix compared to [EOEIM]BF4that was discovered by SEM pictures; On the other hand, according to TGA and MFR analysis, it is found that [PtMIM]BF4/PLA blend exhibits a better thermal stability compared to [EOEIM]BF4/PLA blends, leading to a lower degradation in [PtMIM]BF4/PLA blend during the melt process. As a result,[PtMIM]BF4/PLA blends exhibit better tensile properties than that of [EOEIM]BF4/PLA blends in the same proportion of PLA and ILs.2. According to the calculation results from isothermal crystallization kinetics for the ILs/PLA blends, it was found that the value of Avrmai exponent n is around2.5for all the samples, indicating that [PtMIM]BF4and [EOEIM]BF4could not affect the nucleating and growth modes of PLA crystal. However, the value of the crystallization half time (t1/2) increased with the increase of ILs content. The strong interaction between imidazole rings of [PtMIM]BF4/or [EOEIM]BF4and PLA macromolecular chain was comfirmed by FTIR analysis, which maybe hinder the crystallization of PLA matrix. The hindering effect of ILs on PLA crystallization is agreement with the observation of POM. In addition, XRD results show that all the crystal forms in neat PLA and both the ILs/PLA blends are a form.3. The flame retardant properties of1-buryl-3-methylimidazolium dibutylphosphate (BMIM(C4H9O)2PO2)/PLA blends were studied. And the results elucidated that the incorporation of a small amount of BMIM(C4H9O)2PO2(0.5wt%-3wt%) could significantly promote the flame retardant properties of PLA blends. The value of LOI increases from23%for neat PLA to33.5%when the content of BMIM(C4H9O)2PO2increases to2.5wt%. And the UL-94V-0rating could be achieved with a BMIM(C4H9O)2PO2) content of2.5wt%in the PLA blends. The significant improvement in flame retardant property can be attributed to phosphate ester structure of BMIM(C4H9O)2PO2and uniform disperse of IL phases in PLA matrix.Furthermore, it is found that BMIM(C4H9O)2PO2could not improve the toughness of PLA. With the increase of IL content, the tensile property of PLA blends decreases gradually.4. The non-isothermal crystallization behaviors of talc/BMIM(C4H9O)2PO2/PLA blends were measured and researched. It is confirmed that the combination of talc and BMIM(C4H9O)2PO2shows a synergistic effect on PLA crystallization. |
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