Processing of poly(lactic acid): characterization of chemical structure, thermal stability and mechanical properties
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Abstract
The processing of poly(lactic acid) (injection and extrusion/injection) as well as annealing of processed
materials were studied in order to analyze the variation of its chemical structure, thermal degradation
and mechanical properties. Processing of PLA was responsible for a decrease in molecular weight, as
determined by GPC, due to chain scission. The degree of crystallinity was evaluated by means of
differential scanning calorimetry and X-ray diffraction. It was found that mechanical processing led to
the quasi disappearance of crystal structure whereas it was recovered after annealing. These findings
were qualitatively corroborated by means of FTIR. By analyzing 1H NMR and 13C NMR chemical shifts and
peak areas, it was possible to affirm that the chemical composition of PLA did not change after processing,
but the proportion of methyl groups increased, thus indicating the presence of a different
molecular environment. The thermal stability of the various materials was established by calculating
various characteristic temperatures from thermograms as well as conversion and conversion derivative
curves. Finally, the mechanical behaviour was determined by means of tensile testing (Young modulus,
yield strength and elongation at break).Peer Reviewe