Document Detail

Formation of Shish-kebabs in Injection-Molded Poly(L-lactic acid) by Application of an Intense Flow Field.
MedLine Citation:
PMID:  23153180     Owner:  NLM     Status:  Publisher    
Unlike polyolefins (e.g., isotactic polypropylene), it is still a great challenge to form rich shish-kebabs in biodegradable poly(L-lactic acid) (PLLA) because of its short chain length and semi-rigid chain backbone. In the present work, a modified injection molding technology, named oscillation shear injection molding, was applied to provide an intense shear flow on PLLA melt in mold cavity, in order to promote shear-induced crystallization of PLLA. Additionally, a small amount of poly(ethylene glycol) (PEG) with flexible chains was introduced for improving the crystallization kinetics. Numerous shish-kebabs of PLLA were achieved in injection-molded PLLA for the first time. High-resolution scanning electronic microscopy and two-dimensional small-angle X-ray scattering showed a structure feature of shish-kebabs with a diameter of around 0.7 µm and a long period of ~20 nm. The two-dimensional wide-angle X-ray diffraction results showed that shish-kebabs had more ordered crystalline structure of α-form. A significant improvement of the mechanical properties was obtained; the tensile strength and modulus increased to 73.7 and 1888 MPa from the initial values of 64.9 and 1684 MPa, respectively, meanwhile the ductility is not deteriorated. Interestingly, when shish-kebabs form in the PLLA/PEG system, a bamboo-like bionic structure comprising a hard skin layer and a soft core develops in injection-molded specimen. This unique structure leads to a great balance of mechanical properties, including substantial increments of 26%, 20% and 112% in the tensile strength, modulus, and impact toughness, compared to the control sample. Further exploration will give a rich fundamental understanding in the shear-induced crystallization and morphology manipulation of PLLA, aiming to achieve superior PLLA products.
Huan Xu; Gan-Ji Zhong; Qiang Fu; Jun Lei; Wei Jiang; Benjamin S Hsiao; Zhong-Ming Li
Publication Detail:
Type:  JOURNAL ARTICLE     Date:  2012-11-16
Journal Detail:
Title:  ACS applied materials & interfaces     Volume:  -     ISSN:  1944-8252     ISO Abbreviation:  ACS Appl Mater Interfaces     Publication Date:  2012 Nov 
Date Detail:
Created Date:  2012-11-16     Completed Date:  -     Revised Date:  -    
Medline Journal Info:
Nlm Unique ID:  101504991     Medline TA:  ACS Appl Mater Interfaces     Country:  -    
Other Details:
Languages:  ENG     Pagination:  -     Citation Subset:  -    
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