Degradability of Polyurethanes and Their Blends with Polylactide, Chitosan and Starch

Abstract

One of the methods of making traditional polymers more environmentally friendly is to modify them with natural materials or their biodegradable, synthetic equivalents. It was assumed that blends with polylactide (PLA), polysaccharides: chitosan (Ch) and starch (St) of branched polyurethane (PUR) based on synthetic poly([R,S]-3-hydroxybutyrate) (R,S-PHB) would degrade faster in the processes of hydrolysis and oxidation than pure PUR. For the sake of simplicity in the publication, all three modifiers: commercial PLA, Ch created by chemical modification of chitin and St are called bioadditives. The samples were incubated in a hydrolytic and oxidizing environment for 36 weeks and 11 weeks, respectively. The degradation process was assessed by observation of the chemical structure as well as the change in the mass of the samples, their molecular weight, surface morphology and thermal properties. It was found that the PUR samples with the highest amount of R,S-PHB and the lowest amount of polycaprolactone triol (PCL_triol) were degraded the most. Moreover, blending with St had the greatest impact on the susceptibility to degradation of PUR. However, the rate of weight loss of the samples was low, and after 36 weeks of incubation in the hydrolytic solution, it did not exceed 7% by weight. The weight loss of Ch and PLA blends was even smaller. However, a significant reduction in molecular weight, changes in morphology and changes in thermal properties indicated that the degradation of the samples should occur quickly after this time. Therefore, when using these polyurethanes and their blends, it should be taken into account that they should decompose slowly in their initial life. In summary, this process can be modified by changing the amount of R,S-PHB, the degree of cross-linking, and the type and amount of second blend component added (bioadditives).

Keywords: branched polyurethanes; chitosan; degradability; polyhydroxybutyrate; polylactide; starch.

Figure 1

The weight changes of PUR x/5 (A), PUR x/15 (B) and PUR x/20 (C) after incubation in buffer solution, and dependence of the weight changes after 36 weeks of incubation on the amount of R,S-PHB in the structure of PURs soft segments (D).

Figure 2

The weight changes of PURs and their blends with PLA (A), and Ch and St (B) after incubation in a buffer solution. For comparison, PUR 10/5, PUR 20/5 and PUR 20/15 are also shown.

Figure 3

ATR-FTIR spectra in the range 3000-4000 cm⁻¹ of PUR 10/5 and PUR 10/5+PLA, before and after degradation in hydrolytic (36 weeks) and oxidizing (7 weeks) solutions.

Figure 4

ATR-FTIR spectra in the range 1580-1780 cm⁻¹ of PUR 10/5, PUR 10/5+PLA and PUR 20/5+PLA, before and after degradation in hydrolytic (36 weeks) and oxidizing (7 weeks) solutions.

Figure 5

ATR-FTIR spectra in the range 1580-1780 cm⁻¹ of PUR 20/5, PUR 20/5+St and PUR 20/5+Ch2.5, before and after degradation in hydrolytic (36 weeks) and oxidizing (1 week) solutions.

Figure 6

SEM images of the surface of PUR 20/5 (A,B), PUR 10/5+Ch2.5% (C,D), PUR 20/5+Ch2.5% (E,F) and PUR 10/5+PLA (G,H) before and after incubation in the buffer solution. The samples with Ch were analyzed after 36 weeks of incubation, whereas PUR 10/5+PLA was after 12 weeks.

Figure 6

SEM images of the surface of PUR 20/5 (A,B), PUR 10/5+Ch2.5% (C,D), PUR 20/5+Ch2.5% (E,F) and PUR 10/5+PLA (G,H) before and after incubation in the buffer solution. The samples with Ch were analyzed after 36 weeks of incubation, whereas PUR 10/5+PLA was after 12 weeks.

Figure 7

Microscopic images of the surface of PUR 20/5+PLA and PUR 20/15+PLA samples before (A) and after 12 weeks (B) of incubation in phosphate buffer.

Figure 8

Optical microscope micrographs of the surface of PUR 20/5, PUR 20/5+St and PUR 20/5+St H.

Figure 9

Microscopic micrographs of PUR 0/5 samples before and after 11 weeks of incubation in the oxidizing solution.