Product performance

1.2 Physico-chemical properties

In-situ polymerization of lactic acid oligomers has been analysed by FTIR spectroscopy and gel permeation chromatography.

Infra-red spectroscopy attests the occurence of polymerised lactic acid into wood structure (Figure 8). Indeed, PLA characteristic peaks at 875 cm-1 and 765 cm-1 are superimposed on wood spectra, and the shift of carbonyl absorption band from 1746 to 1764 cm-1 during heating indicates a higher ester linkage content.

Product performance

Fig. 8. FTIR spectra of pine control sample (a), pine after catalysed short (b) and long (c) treatment

 

Polymer extracted from treated samples by chloroform show a noticeable increase and a strong enlargement in molecular weight distribution (Figure 9).

 

Product performance

Fig. 9. GPC chromatograms of impregnated oligomers (A), oligomers extracted from short (B) non catalysed (a) and catalysed (b) treatment, and oligomers extracted from long (C) non catalysed (a) and catalysed (b) treatment

 

After short treatment, oligomers are not durably linked to the wood structure as around 90% weight loss by chloroform extraction is noticed. No characteristic oligomer peaks is noticed in the FTIR spectra neither. After long treatment, around 50% weight loss indicates that half the amount of oligomers remained in wood, either due to physical trapping of the molecules or hydrogen bondings.