Facelift Of PLLA: Effect Of Orientation On Physical Ageing In Poly(L-Lactic Acid) Films | 53335
Journal of Bioremediation & Biodegradation
Like us on:
Our Group organises 3000+ Global Conferenceseries Events every year across USA, Europe & Asia with support from 1000 more scientific Societies and Publishes 700+ Open Access Journals which contains over 50000 eminent personalities, reputed scientists as editorial board members.
Poly(L-lactic acid) (PLLA) is a slow-crystallising polyester which exhibits brittle behaviour due to relatively fast physical
ageing of the amorphous phase. This embrittlement of PLLA narrows its application window in such fields where flexibility
of a polymer is required (e.g., packaging). In this study, we investigated the effects of thermal rejuvenation and molecular
orientation of the amorphous phase on physical ageing of oriented PLLA films with emphasis on mechanical properties.
Uniaxial compression testing showed that physical ageing of the amorphous phase increases the yield stress and the associated
strain softening response, both contributing to the observed embrittlement of PLLA in tension. Moreover, the strainhardening
response was found not to be influenced by physical ageing. Molecular orientation of the amorphous phase at
constant crystallinity was applied by uniaxial and biaxial plastic deformation just above the glass-transition temperature (at
70°C) up to modest plastic strains of 200%, to avoid strain-induced crystallisation. Stress-relaxation experiments combined
with tensile testing both as a function of ageing time have revealed that both uniaxial and biaxial plastic deformation in excess
of 100% plastic strain, decelerates and possibly prohibits the physical ageing process. The oriented monofilaments and films
have improved mechanical properties, such as stiffness, strength and strain-to-break. The latter properties were not affected
by physical ageing during a testing period of 40 days. In addition, plastic deformation to higher draw ratios and/or at slightly
higher temperatures (90°C), strongly enhanced crystallinity and resulted in PLLA monofilaments and films that also exhibited
tough behaviour not affected by physical ageing.
Gagik Ghazaryan is a 3rd year PhD student at the Swiss Federal Institute of Technology Zurich (ETH Zurich), working in the group of Soft Materials. He is also affiliated to the Swiss Federal Laboratories for Materials Science and Technology (Empa) in St. Gallen, Switzerland. He completed his MSc degree in Desalination and Water Treatment at the Ben-Gurion University of the Negev, Israel.