In-situ uniaxial drawing of poly-L-lactic acid (PLLA): Following the crystalline morphology development using time-resolved SAXS/WAXS

POLYMER

卷:193

Article

Heeley, Ellen L.¹  Billimoria, Kharmen²  Parsons, Nathan²  Figiel, Lukasz²  Keating, Elspeth M.³  Cafolla, Conor T.³  Crabb, Eleanor M.¹  Hughes, Darren J.³ 

[1] Open Univ, Fac Sci Technol Engn & Math, Walton Hall, Milton Keynes MK7 6AA, Bucks, England

[2] Univ Warwick, IINM, WMG, Coventry CV4 7AL, W Midlands, England

[3] Univ Warwick, WMG, Coventry CV4 7AL, W Midlands, England

关键词: Poly-L-lactic acid;    Uniaxial deformation;    SAXS/WAXS;    Crystalline morphology;    Orientation;   

DOI  :  10.1016/j.polymer.2020.122353

来源: Elsevier

【 摘 要 】

Simultaneous synchrotron small- and wide-angle X-ray scattering (SAXS/WAXS) was used to follow the crystalline morphology evolution of poly-L-lactic acid (PLLA) during uniaxial deformation at various draw temperatures (T-d). The mechanical behaviour of PLLA, was found to be strongly dependent on T-d. 2D SAXS/WAXS data taken during the draw showed that at low T(d)s cavitation and voiding occurred and the initial crystallites underwent 'overdrawing' where they slip and are partially destroyed. SEM confirmed that surface voiding and cavitation had occurred at T-d = 60 and 65 degrees C but was absent at higher T(d)s. During the draw, no long-range macromolecular lamellar structure was seen in the SAXS, but small crystallites of the disordered alpha' crystal form of PLLA were observed in the WAXS at all T(d)s. The PLLA samples were then step annealed in a second processing stage (post-draw) to develop the oriented crystalline lamellar structure and increase the amount of the stable a crystalline form. SAXS/WAXS data showed that a highly oriented lamellar stack macrostructure developed on annealing, with increased crystallite size and crystallinity at all T(d)s. Furthermore, step annealing drove the crystalline transition in all samples from the disordered alpha' crystal form to the stable alpha crystal form. Therefore, varying pre- and post-processing parameters can significantly influence the mechanical properties, orientation, crystalline morphology and crystal phase transition of the final PLLA material.

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