Abstract
The synergistic effect of nucleating agents and plasticizers on the thermal and mechanical performance of PLA nanocomposites was investigated with the objective of increasing the crystallinity and balancing the stiffness and toughness of PLA mechanical properties. Calcium carbonate, halloysite nanotubes, talc and LAK (sulfates) were compared with each other as heterogeneous nucleating agents. Both the DSC isothermal and non-isothermal studies indicated that talc and LAK were the more effective nucleating agents among the selected fillers. Poly(d-lactic acid) (PDLA) acted also as a nucleating agent due to the formation of the PLA stereocomplex. The half crystallization time was reduced by the addition of talc to about 2 min from 37.5 min of pure PLA by the isothermal crystallization study. The dynamic mechanical thermal study (DMTA) indicated that nanofillers acted as both reinforcement fillers and nucleating agents in relation to the higher storage modulus. The plasticized PLA studied by DMTA indicated a decreasing glass transition temperature with the increasing of the PEG content. The addition of nanofiller increased the Young’s modulus. PEG had the plasticization effect of increasing the break deformation, while sharply decreasing the stiffness and strength of PLA. The synergistic effect of nanofillers and plasticizer achieved the balance between stiffness and toughness with well-controlled crystallization.
Highlights
(lactic acid) has been the subject of much attention because of its outstanding performance in terms of high stiffness and strength, biodegradability and thermal processability and is often seen as an alternative to traditional petrochemical plastic [1,2]
polyethylene glycol (PEG) acts as a plasticizer to decrease the glass transition temperature and improve the chain mobility, while LAK acts as a nucleating agent to increase the crystallinity
The enhanced crystallization under the traditional molding process of PLA nanocomposites was attributed to the effective nucleating agents
Summary
(lactic acid) has been the subject of much attention because of its outstanding performance in terms of high stiffness and strength, biodegradability and thermal processability and is often seen as an alternative to traditional petrochemical plastic [1,2]. A suitable selection of the PLA commercial grade with different L-/D- ratios is critical for the requirement of the conversion processing conditions and specific properties In processes, such as injection molding, where the orientation is limited with a high cooling speed, it is much more difficult to develop significant crystallinity, and formulation or processing modifications are necessary. Nucleating agents can be added to PLA for the promotion of crystallinity via traditional processing, such as injection molding, under a suitable thermal history and cycle time. It is shown that the crystallization half-time can be required by more than one order of magnitude to less be than 1 min when 1% talc is added [8] Another reported potential nucleating agent in the literature is the stereocomplex of PLLA and Poly(D-lactic acid). The relationship between crystallinity and mechanical properties was investigated by dynamic mechanical thermal analysis (DMTA) and tensile measurements
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