Beyond a Model of Polymer Processing-Triggered Shear: Reconciling Shish-Kebab Formation and Control of Chain Degradation in Sheared Poly(L-lactic acid)
2015 (English)In: ACS SUSTAINABLE CHEMISTRY & ENGINEERING, ISSN 2168-0485, Vol. 3, no 7, 1443-1452 p.Article in journal (Refereed) Published
Here we disclose an unprecedented methodology toward high-performance poly(L-lactic acid) (PLLA) through generation of dense shish-kebabs, while the normal shear stress-induced chain degradation is controlled. The key elements involve the application of a pulse of strong shear and controlled crystallization. Specifically, the shear featuring a short duration of 1 s and a shear rate high to 100 s(-1) was employed to create shish precursors, which was followed by high-temperature crystallization (at 130, 135, and 140 degrees C) to render the prevailing development of shish-kebabs rather than spherulites. The direct observation of the overgrown shish afforded the demonstration of its origin from shear-aligned bundles of fibrillar chains, implying the crucial importance of chain entanglements in driving the alignment of neighboring chains along the transient shear. For the first time, the shear-aligned shish was revealed to present much higher conformational order, compared to the neighboring kebabs or spherulites. It is of great interest that the application of transient shear flow prevented PLLA from shear-induced degradation, although the PLLA chains are inherently sensitive to external shear stress. The proposed pathway, thus, creates PLLA rich in shish-kebabs with well-preserved high-molecular-weight chains. This signifies a new scenario with respect to previous studies where strong and long-acting shear was required for the formation of oriented structures in PLLA and the property enhancement was to large part hampered by simultaneous chain scissions. Of immense significance is the possibility to utilize these findings during common processing such as extrusion, spinning, and blowing, in which a transient and intensive shear flow is normally generated.
Place, publisher, year, edition, pages
2015. Vol. 3, no 7, 1443-1452 p.
A pulse of shear, Poly(L-lactic acid), Cylindrite, Shish-kebab, Conformational ordering, Chain degradation
IdentifiersURN: urn:nbn:se:kth:diva-171897DOI: 10.1021/acssuschemeng.5b00320ISI: 000357708800023ScopusID: 2-s2.0-84936803142OAI: oai:DiVA.org:kth-171897DiVA: diva2:845923
QC 201508132015-08-132015-08-102015-08-13Bibliographically approved