Viscoelastic Effects of Long-Chain Acyl-Group Substituents on Molten Paramylon Mixed Esters

• Published in: Journal of polymers and the environment Vol. 30; no. 6; pp. 2270 - 2279
• Main Authors: Shibakami, Motonari, Kawata, Yuki
• Format: Journal Article
• Language: English
• Published: New York Springer US 01.06.2022; Springer Nature B.V
• Subjects: Acetic acid; Aggregates; Chemistry; Chemistry and Materials Science; Diffraction patterns; Environmental Chemistry; Environmental Engineering/Biotechnology; Esters; Industrial Chemistry/Chemical Engineering; Loss modulus; Materials Science; Molecular chains; Molecular weight; Original Paper; Polymer Sciences; Polymers; Rheological properties; Size exclusion chromatography; Substitutes; Viscoelasticity; Viscosity; X ray analysis; X-ray diffraction; Dynamic viscoelastic measurement; Master curve; Thermoplastics; Paramylon mixed ester; Activation energy; Molten state aggregation
• ISSN: 1566-2543; 1572-8919
• DOI: 10.1007/s10924-021-02346-5

Rheological analysis using multiple frequencies and different temperatures and X-ray analysis were performed on previously synthesized paramylon acetate laurates and paramylon acetate myristates with three different degrees of substitution [DSs; 0.56 or 0.50 (high), 0.39 or 0.35 (moderate), 0.20 or 0.19 (low)] of long-chain acyl groups to gain insight into their dynamic behaviors in the molten state. Examination of the X-ray diffraction patterns and differential scanning calorimetric thermograms previously obtained suggested that the main chains of the paramylon mixed esters are plausibly in a partially ordered state with flexible acyl chains in the molten state. Comparison of the complex viscosity master curves indicated that DS0.39 substitution led to the highest complex viscosity among the laurates, while DS0.35-myristate led to the lowest viscosity among the myristates irrespective of similar DS values. Further comparison between the DS0.39-laurate and DS0.35-myristate indicated that the former shows a viscosity more than one order of magnitude larger than the latter in the lower-frequency region [ω <  ~ 10 2 (rad/s)]. The frequency of crossover points of the storage and loss modulus master curves, which are related to molecular weight in the molten state, revealed that the lauroyl and myristoyl, respectively, exhibited the largest and smallest molecular weights among the six tested products. Given that both the products had similar weight average and number average molecular weights in the infinitely diluted state (5.45 and 4.76 × 10 5 for the laurate, 5.09 and 3.76 × 10 5 for the myristate), as indicated by size exclusion chromatography, the difference in molecular weight is attributable to the difference in polymer aggregate size in the molten state; the laurate forms a large aggregate, and the myristate either forms a small aggregate or no aggregate at all. Hence, the complex viscosity difference between the laurate and myristate is attributable to the polymer aggregate size in the molten state. The similarity of the flow activation energy (200.0 kJ/mol for the laurate, 196.8 kJ/mol for the myristate) calculated from the Arrhenius plot of the shift factor versus the reciprocal of temperature implies that the constituent polymers of the aggregates are in the dynamic state.