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Recovery as a measure of oriented crystalline structure in poly(l-lactide) used as shape memory polymer / Y.S. Wong in Acta materialia, Vol. 58 N° 1 (Janvier 2010) 

Public ISBD [article]  in Acta materialia > Vol. 58 N° 1 (Janvier 2010) . - pp. 49–58 Titre : Recovery as a measure of oriented crystalline structure in poly(l-lactide) used as shape memory polymer Type de document : texte imprimé Auteurs : Y.S. Wong, Auteur ; S.S. Venkatraman, Auteur Année de publication : 2010 Article en page(s) : pp. 49–58 Note générale : Métallurgie Langues : Anglais (eng) Mots-clés : Poly(l-lactide)  Recovery Résumé : Semicrystalline poly(l-lactide), or PLLA, has been reported as possessing shape-memory effect [1], [2], [3], [4] and [5]; however, the mechanism responsible for the shape recovery has not been well addressed. Therefore, in this paper, we attempted to investigate the structural evolution in PLLA during the shape memory process by means of differential scanning calorimetry, dynamic mechanical analysis (DMA), optical birefringence and wide-angle X-ray diffraction measurements. The shape recovery behaviour and recovery stress as a function of stretch ratio and deformation temperature were quantified. Based on the present results, shape recovery decreases with increasing stretch ratio and deformation temperature. It is suggested that the shape recovery is associated with the disorientation of oriented amorphous chains formed during stretching and the drop in recovery is attributed to the strain-induced crystallization and the formation of highly oriented microfibrillar structure, hindering the mobility in the amorphous phase and thus impeding recovery. In particular, the validity of the stress-optical law is considered. It is shown that the stress-optical properties show divergence from the Gaussian theory for stretch ratio greater than ∼1.5. DEWEY : 669 ISSN : 1359-6454 En ligne : http://www.sciencedirect.com/science/article/pii/S1359645409005680 [article] Recovery as a measure of oriented crystalline structure in poly(l-lactide) used as shape memory polymer [texte imprimé] / Y.S. Wong, Auteur ; S.S. Venkatraman, Auteur . - 2010 . - pp. 49–58. Métallurgie Langues : Anglais (eng) in Acta materialia > Vol. 58 N° 1 (Janvier 2010) . - pp. 49–58 Mots-clés : Poly(l-lactide)  Recovery Résumé : Semicrystalline poly(l-lactide), or PLLA, has been reported as possessing shape-memory effect [1], [2], [3], [4] and [5]; however, the mechanism responsible for the shape recovery has not been well addressed. Therefore, in this paper, we attempted to investigate the structural evolution in PLLA during the shape memory process by means of differential scanning calorimetry, dynamic mechanical analysis (DMA), optical birefringence and wide-angle X-ray diffraction measurements. The shape recovery behaviour and recovery stress as a function of stretch ratio and deformation temperature were quantified. Based on the present results, shape recovery decreases with increasing stretch ratio and deformation temperature. It is suggested that the shape recovery is associated with the disorientation of oriented amorphous chains formed during stretching and the drop in recovery is attributed to the strain-induced crystallization and the formation of highly oriented microfibrillar structure, hindering the mobility in the amorphous phase and thus impeding recovery. In particular, the validity of the stress-optical law is considered. It is shown that the stress-optical properties show divergence from the Gaussian theory for stretch ratio greater than ∼1.5. DEWEY : 669 ISSN : 1359-6454 En ligne : http://www.sciencedirect.com/science/article/pii/S1359645409005680