Glycolysis of Polyurethanes Composites Containing Nanosilica

Abstract

Rigid polyurethane (RPU) foams have been successfully glycolyzed by using diethylene glycol (DEG) and crude glycerol (CG) as transesterification agents. However, DEG did not allow to achieve a split-phase process, obtaining a product with low polyol purity (61.7 wt %). On contrary, CG allowed to achieve a split-phase glycolysis improving the recovered polyol purity (76.5%). This is an important novelty since, up to now, RPUs were glycolyzed in single-phase processes giving products of low polyol concentration, which reduced the further applications. Moreover, the nanosilica used as filler of the glycolyzed foams was recovered completely pure. The recovered polyol successfully replaced up to 60% of the raw polyol in the synthesis of RPU foams and including the recovered nanosilica in the same concentration than in glycolyzed foam. Thus, the feasibility of the chemical recycling of this type of polyurethane composites has been demonstrated. Additionally, PU foams were synthesized employing fresh nanosilica to evaluate whether the recovered nanosilica has any influence on the RPU foam properties. These foams were characterized structurally, mechanically and thermally with the aim of proving that they met the specifications of commercial foams. Finally, the feasibility of recovering the of CG by vacuum distillation has been demonstrated.

Keywords: crude glycerol; glycolysis; mechanical properties; nanosilica; polyurethane composites; rigid polyurethane foams; thermal properties.

Scheme 1

Polyurethane glycolysis reaction.

Scheme 2

Sequence of the performed experiments.

Scheme 3

Polyurethane glycolysis reaction using DEG (a) or CG (b) as a glycolysis agent.

Figure 1

(a) Experimental device for the materials thermal behavior tests. (b) Temperature and heat flux sensors positions.

Figure 2

GPC chromatograms of the glycolysis product at 360 min in comparison with GPC chromatograms of raw rigid polyether polyol and DEG. Peaks I, II, III and IV = rigid polyether polyol; Peak V = reaction byproducts; Peak VI = DEG.

Figure 3

FTIR spectra of the raw polyol and the product obtained from the glycolysis reaction.

Figure 4

GPC chromatograms of the UP and BP at 360 min and of raw rigid polyether polyol and crude glycerol. Peaks I, II, III and IV = rigid polyether polyol; Peak V = reaction by-products; Peak VI = Crude glycerol.

Figure 5

FTIR spectra of the raw polyol and the upper and bottom phases from the glycolysis reaction.

Figure 6

Comparison of FTIR spectra of the fresh and recovered nanosilica.

Figure 7

XRD analysis of fresh and recovered nanosilica.

Figure 8

DLS analysis of fresh (a) and recovered nanosilica (b).

Figure 9

SEM pictures of fresh (a) and recovered nanosilica (b) with magnification of ×50,000.

Figure 10

FTIR analysis of the synthesized foams using recovered polyol as a replacement of raw rigid polyol and fresh or recovered nanosilica.

Figure 11

SEM micrographs with magnification ×100 of the PU foams with different proportions of recovered polyols with recovered nanosilica (a) and 0% recovered polyol with fresh nanosilica (b) and without nanosilica (c).

Figure 12

GPC chromatograms of the BP and the raffinate and extract after distillation. Peaks I = rigid polyether polyol; Peak II = reaction by-products; Peak III = Crude glycerol.

Figure 13

Comparison of FTIR spectra of the raw and recovered crude glycerol.