Characteristics of polylactide composites involving montmorillonite and boron compounds

Akar, Alinda Öykü
Poly(lactic acid) (PLA) is a biodegradable and biocompatible polymer and it is accepted as a promising alternative to the petroleum based materials. The main objective of this study is to investigate the effect of the type and the amount of boron compounds with the addition of nanoclay to thermal, mechanical properties and flame retardancy of poly(lactic acid) (PLA) based nanocomposites. By this aim, zinc borate (ZnB), benzene-1,4-diboronic acid (BDBA) and Cloisite 30B (C30B) are used as an additive in PLA matrix. SEM images of composites indicated homogeneous dispersion of boron compounds in PLA matrix for low concentrations. Agglomerations are observed as the amount of additives is increased. TEM analyses of PLA nanocomposites indicated intercalated structures. Characteristic Bragg peak of nanoclay disappeared in the XRD diffractograms of nanocomposites in accordance to TEM results. DSC results pointed out increase in melting temperatures upon incorporation of boron compounds into PLA matrix. TGA analyses revealed that inclusion of boron compounds causes reduction in thermal stability but improvement in char yield of PLA matrix. Generation of cyclic oligomeric products, protonated oligomers and low mass fragments were observed during the pyrolysis of the composites including boron compounds. These reactions, although cause decomposition of PLA chains at low concentrations of boron compounds to a certain extent, generate a cross-linked structure increasing thermal stability at high concentrations of boron compounds. Increase in relative yields of products due to cis-elimination reactions after nanoclay addition was also observed. Incorporation of C30B into PLA composites further increases thermal stability of PLA composites involving BDBA, but, in general, causes a decrease in thermal stability of composites involving ZnB. Tensile tests indicated that ZnB addition causes increase in tensile strength whereas BDBA addition results in decrease of percent elongation values. No significant difference between flame retardancy of PLA and its composites was detected by UL-94 test. According to LOI test results, addition of boron compounds gives slight improvement on LOI value and the highest LOI value was recorded for ZnB and nanoclay containing composites.


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Citation Formats
A. Ö. Akar, “Characteristics of polylactide composites involving montmorillonite and boron compounds,” M.S. - Master of Science, Middle East Technical University, 2016.