Composites Research

The Korean Society for Composite Materials (한국복합재료학회)
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A Molecular Dynamics Simulation Study on the Thermoelastic Properties of Poly-lactic Acid Stereocomplex Nanocomposites

분자동역학 전산모사를 이용한 폴리유산 스테레오 콤플렉스 나노복합재의 가수분해에 따른 열탄성 물성 예측 연구

  • Ki, Yelim (School of Energy Systems Engineering, Chung-Ang University) ;
  • Lee, Man Young (The 4th R&D Institute - 4, Agency for Defense Development) ;
  • Yang, Seunghwa (School of Energy Systems Engineering, Chung-Ang University)
  • Received : 2018.08.06
  • Accepted : 2018.11.09
  • Published : 2018.12.31
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Abstract

In this study, the thermoelastic properties of poly lactic acid (PLA) based nanocomposites are predicted by molecular dynamics (MD) simulation and a micromechanics model. The stereocomplex mixed with L-lactic acid (PLLA) and D-lactic acid (PDLA) is modeled as matrix phase and a single walled carbon nanotube is embedded as reinforcement. The glass transition temperature, elastic moduli and thermal expansion coefficients of pure matrix and nanocomposites unit cells are predicted though ensemble simulations according to the hydrolysis. In micromechanics model, the double inclusion (D-I) model with a perfect interface condition is adopted to predict the properties of nanocomposites at the same composition. It is found that the stereocomplex nanocomposites show prominent improvement in thermal stability and interfacial adsorption regardless of the hydrolysis. Moreover, it is confirmed from the comparison of MD simulation results with those from the D-I model that the interface between CNT and the stereocomplex matrix is slightly weak in nature.

본 연구에서는 폴리유산 나노복합재의 열탄성 거동을 예측하기 위해 분자동역학 전산모사를 수행하고 그 결과를 열탄성 미시역학 모델 예측해와 비교하였다. 폴리유산의 두 이성질체인 D유산(Poly D-lactide)와 L유산(Poly L-lactide)을 혼합한 스테레오 콤플렉스를 모델링하였고 이들을 기지로 사용한 탄소나노튜브 나노복합재를 구성하였다. 유산의 분해 유무에 따른 유리전이온도와 탄성계수 그리고 열팽창계수를 앙상블 전산모사를 통해 예측하였다. 미시역학 모델에서는 계면의 완전 결합을 가정한 이중입자 모델을 적용하여 탄성계수와 열팽창계수를 동일한 조성에서 예측하였다. 그 결과 열적 안정성에 있어 스테레오 콤플렉스에 탄소나노튜브가 첨가될 경우 유산의 뛰어난 계면 흡착과 이에 따른 열적 안정성 향상을 보였다. 순수한 유산과 나노복합재 모두 가수 분해에 따른 열적 특성 변화는 관찰되지 않았다. 또한, 스테레오 콤플렉스와 나노튜브 간 계면은 약한 불완전 결합상태 임을 알 수 있었다.

Keywords

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Fig. 1. Molecular structures of stereocomplex and nanocomposites

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Fig. 2. Stress-Strain curve of stereocomplex

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Fig. 3. Stress-Strain curves of nanocomposite; (a) Longitudinal tension (b) Transverse tension

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Fig. 4. Temperature-volume relation graph of stereocomplex before & after hydrolysis

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Fig. 5. Temperature-volume relation graph of stereocomplex/CNT before & after hydrolysis

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Fig. 6. Comparison of thermal expansion coefficient of nanocomposite determined from molecular dynamics simulation and double inclusion model

Table 1. Comparison of interaction energy between stereocomplex and carbon nanotube before & after hydrolysis

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Table 2. Elastic Modulus of nanocomposite before & after hydrolysis

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Table 3. Glass transition temperature before & after hydrolysis

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Table 4. Thermal expansion coefficient of stereocomplex before & after glass transition

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Table 5. Thermal expansion coefficient of nanocomposite before & after glass transition

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