Toughening of polylactic acid by starch based nanocapsule
To address the two problems of brittleness and high price of polylactic acid(PLA)material itself,the mechanical properties of PLA composites were investigated and analyzed by constructing nanocapsules based on biodegradable and cheap starch,which was then added as a nano-filler to the PLA matrix.By varying the ratio of hydroxyethyl starch(HES)/polyethylene glycol(PEG-400),2,4'-and 4,4'-diphenylmethane diisocyanate mixtures(MDI-50),nanocapsules with different compositions were prepared and the mechanism of the toughening effect of the nanocapsules for PLA was explored.The morphology,composition and size of the nanocapsules were characterized in detail using transmission electron microscopy,Fourier transform infrared spec-troscopy and dynamic light scattering;the mechanical properties of the PLA composite films were tested using a universal testing machine;and the toughening mechanism of the nanocapsules was discussed by the calculated average particle size between the nano-capsules and the results of the differential scanning calorimetry test.The results show that the average diameter of the nanocapsules is about 120 nm and the prepared PLA composites have excellent toughness,which is increased by up to 909% compared with the pure PLA film;there exists a critical intergranular distance between the average distance between the nanocapsules,239 nm to 162 nm,which results in an abrupt increase in the toughness of the matrix and meets the critical requirements for the brittle-to-toughness transition;as the viscoelasticity increases,the toughening effect of nanocapsules also increases,which is negatively correlated with the glass transition temperature of nanocapsules.
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