Thermal analysis of spider silk inspired di-block copolymers in the glass transition region by TMDSC
We used advanced thermal analysis methods to characterize a new family of A-B di-block copolymers based on the amino acid sequences of Nephila clavipes major ampulate dragline spider silk. Using temperature modulated differential scanning calorimetry with a thermal cycling method and thermogravimetry, we captured the effect of bound water acting as a plasticizer for spider silk-like biopolymer films which had been cast from water solution and then dried. A low glass transition because of bound water removal was observed in the first heating cycle, after which, a shift of glass transition was observed in A-block film due to crystallization and annealing, and in BA film due to annealing. No shift of glass transition after bound water removal was observed in B-block film. The reversing heat capacities, Cp, for temperatures below and above the glass transition were measured and compared to the calculated values. The solid state heat capacity was modeled below Tg, based on the vibrational motions of the constituent poly(amino acid)s, heat capacities of which are known from the ATHAS Data Bank. Excellent agreement was found between the measured and calculated values of the heat capacity, showing that this model can serve as a standard method to predict the solid state Cp for other biologically inspired block-copolymers. We also calculated the liquid state heat capacities of the 100% amorphous biopolymer at Tg, and this predicted value can be use to determined the crystallinity of protein-based materials.
KeywordsNephila Clavipes spider dragline silk Block copolymer Heat capacity Glass transition Temperature modulated differential scanning calorimetry X-ray diffraction
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