Synthesis and characterization of paramylon propionate-graft- poly(lactic acid) and paramylon propionate-graft-poly(ε-caprolactone)

Effects of Molecular Weight on the Marine Biodegradability of Poly(l-lactic acid)

Poly(l-lactic acid) (PLA) is a biodegradable bioplastic with limited marine degradation. This study examines the impact of molecular weight on PLA's marine biodegradability. We synthesized PLA with terminal hydroxyl groups (PLA-OH) with degrees of polymerization (DP) between 14 and 642 and conducted biochemical oxygen demand (BOD) tests. Samples with a DP of 422 or 642 did not degrade, like commercial PLA. However, PLA-OH with a DP below 314 showed biodegradability, with DP 14 exhibiting a higher degradability than cellulose. Size exclusion chromatography (SEC) confirmed a decrease in molecular weight for samples with DPs below 314, indicating extracellular microbial activity. These findings suggest that PLA-OH with a DP under 314 can be degraded in marine conditions, unlike high-molecular-weight PLA. If the DP of high-molecular-weight PLA can be reduced to 314 by some specific method, then it is expected that PLA can be used to create marine biodegradable materials.

A review of paramylon processing routes from microalga biomass to non-derivatized and chemically modified products

Paramylon is a linear β-1,3-glucan, similar to curdlan, produced as intracellular granules by the microalga Euglena gracilis, a highly versatile and robust strain, able to grow under various trophic conditions, with valorization of CO_2, wastewaters, or food byproducts as nutrients. This review focuses in particular on the various processing routes leading to new potential paramylon based products. Due to its crystalline structure, involving triple helices stabilized by internal intermolecular hydrogen bonds, paramylon is neither water-soluble nor thermoplastic. The few solvents able to disrupt the triple helices, and to fully solubilize the polymer as random coils, allow non derivatizing shaping into films, fibers, and even nanofibers by a specific self-assembly mechanism. Chemical modification in homogeneous or heterogeneous conditions is also possible. The non-selective or regioselective substitution of the hydroxyl groups of glucosidic units leads to water-soluble ionic derivatives and thermoplastic paramylon esters with foreseen applications ranging from health to bioplastics.

Synthesis of thermoplastic chitin hexanoate-graft-poly(ε-caprolactone)

Herein, we report that chitin hexanoate-graft-poly(ε-caprolactone) (ChHex-g-PCL) is thermoplastic, as confirmed by the formation of a melt-pressed film. Chitin hexanoates with degrees of substitution (DSs) of 1.4-1.8 and bearing free hydroxy groups were first prepared by the hexanoylation of chitin using adjusted feed equivalents of hexanoyl chloride in the presence of pyridine and N,N-dimethyl-4-aminopyridine in 1-allyl-3-methylimidazolium bromide, an ionic liquid. Surface-initiated ring-opening graft polymerization of ε-caprolactone from the hydroxy groups of the chitin hexanoates was conducted in the presence of tin(II) 2-ethylhexanoate as the catalyst at 100 °C to produce (ChHex-g-PCL)s. The feed equivalent of the catalyst, reaction time, and DS value were found to affect the molar substitution and degree of polymerization of the PCL graft chains. Longer PCL graft chains formed their crystalline structures and the (ChHex-g-PCL)s largely contained uncrystallized chitin chains. Accordingly, these (ChHex-g-PCL)s exhibited melting points associated with the PCL graft chains, leading to thermoplasticity.