Improving the Processability and Performance of Micronized Fiber-Reinforced Green Composites through the Use of Biobased Additives

Abstract

Green composites made of bioplastics reinforced with natural fibers have gained considerable attention over recent years. However, the use of natural fibers in composites usually compromise some key properties, such as the impact strength and the processability of the final materials. In the present study, two distinct additives, namely an epoxidized linseed oil (ELO) and a sugar-based surfactant, viz. GlucoPure^® Sense (GPS), were tested in composite formulations of poly(lactic acid) (PLA) or poly(hydroxybutyrate) (PHB) reinforced with micronized pulp fibers. Both additives showed a plasticizing effect, which led to a decrease in the Young's and flexural moduli and strengths. At the same time, the elongation and flexural strain at break were considerably improved on some formulations. The melt flow rate was also remarkably improved with the incorporation of the additives. In the PHB-based composites, an increment of 230% was observed upon incorporation of 7.5 wt.% ELO and, in composites based on PLA, an increase of around 155% was achieved with the introduction of 2.5 wt.% GPS. ELO also increased the impact strength to a maximum of 29 kJ m^-2, in formulations with PLA. For most composites, a faster degradation rate was observed on the formulations with the additives, reaching, in the case of PHB composites with GPS, a noteworthy weight loss over 75% under burial testing in compost medium at room temperature.

Keywords: biodegradability; cellulose; epoxidized linseed oil; green composites; mechanical properties; micronized fibers; poly(hydroxybutyrate); poly(lactic acid); sugar-based surfactant; thermal properties.

Figure 1

Schematic illustration of the experimental procedure and photographs of the injection-molded specimens of poly(hydroxybutyrate) (PHB) and poly(lactic acid) (PLA)-based composites reinforced with cellulose micronized fibers with different percentages of GPS and ELO additives.

Figure 2

SEM micrographs of the fractured surfaces of PHB- and PLA-based composites without additives and with different contents of GPS and ELO additives.

Figure 3

Tensile mechanical properties of the PHB- and PLA-based composites without additives and with GPS (A,C,E) and ELO (B,D,F) additives. Different letters (a,b,c,d) indicate statistically significant differences (p  <  0.05).

Figure 4

Flexural mechanical properties of the PHB- and PLA-based composites without additives and with GPS (A,C,E) and ELO (B,D,F) additives. Different letters (a,b,c,d) indicate statistically significant differences (p  <  0.05).

Figure 5

Impact strength of the PHB- (A) and PLA-based composites (B) without additives and with different loads of GPS and ELO additives (the lines are for visual guidance only). Different letters (a,b,c) or (α,β,γ) indicate statistically significant differences (p  <  0.05).

Figure 6

Melt flow rate of the PHB- (A) and PLA-based composites (B), without additives and with different loads of GPS and ELO additives (the lines are for visual guidance only). Different letters (a,b) or (α,β,γ) indicate statistically significant differences (p  <  0.05).

Figure 7

Water uptake capacity of the PHB- (A) and PLA-based composites (B) without additives and with different loads of GPS and ELO additives (the lines are for visual guidance only).

Figure 8

Weight loss as a function of time for the PHB- (A) and PLA-based composites (B) without additives and with different loads of GPS and ELO additives. The standard deviations (not shown) are under 7.6% for PHB-based materials and under 3.9% for PLA-based materials, and the lines are for visual guidance only.

Figure 9

Digital photographs of the test specimens prior and after burial tests in compost medium for 30, 60, 90, 12 and 180 days.