Identifying transition temperatures in bloodmeal-based thermoplastics using material pocket DMTA
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Bloodmeal can be used to manufacture thermoplastics, but requires water, urea, sodium sulphite, and sodium dodecyl sulphate to modify chain mobility. Transition temperatures of bloodmeal, modified bloodmeal, and processed bloodmeal-based thermoplastics were compared using material pocket dynamic mechanical thermal analysis. The glass transition temperature (T g) of bloodmeal dropped from 493 to 263 K using only water as a plasticizer but was restored when freeze dried. Modifying bloodmeal lowered T g to 193 K. This was raised by drying, but not to that of unmodified bloodmeal indicating a permanent change. Three additional transitions were identified above T g, for modified bloodmeal between 300 and 480 K. These were thought to be transitions of dehydrated bulk amorphous regions, amorphous regions between crystallites and chains segments in crystallites and were also seen at lower temperatures when replacing some water with tri-ethylene glycol (TEG). Material pockets increased resolution in processed samples. One broad T g was observed in consolidated bars, at 335 or 350 K with or without TEG. In material pockets, these resolved into three transitions, similar to those observed before processing. Changes in relative magnitudes suggested some chain rearrangement leading to more bulk amorphous regions. Differences were detected between onset of drop in storage modulus and peaks in loss modulus and tan δ in pockets or bars, but generally led to the same conclusions. For bar samples, it was helpful to compare natural and log modulus scales. Good practice would use all these techniques in parallel to correctly identify relaxation temperatures.
KeywordsRelaxation Dynamic mechanical thermal analysis (DMTA) Thermoplastic protein Bioplastics Glass transition
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