Abstract
Density reduction has become a topical issue in wood composite materials for application in building and furniture. In this study, lightweight wood–polyurethane (W–PU) composite foams with the addition of 30 wt% wood particles were prepared. Industrial kraft lignin was used as bio-polyol to substitute partial petroleum-based diethylene glycol (DEG) to synthesize rigid W–PU foams. The effect of varying lignin contents (5, 10, 15 and 20 wt% based on DEG mass) on the reactivity, morphology, density, compressive properties, water absorption and thermal stability of the foams was evaluated. Fourier transform infrared (FTIR) analysis confirmed the formation of characteristic urethane linkages in all the foam samples. With the incorporation of lignin, the foam cellular shape became irregular with formation of large cells. W–PU foams exhibited poor cellular structures with a larger number of open cells. The density of W–PU foams increased from 47 to 96 kg/m3 as the lignin content increased from 0 to 20%. Although the foam reactivity was decreased by the incorporation of lignin, both the compressive strength and modulus were increased upon the incorporation of lignin. Furthermore, the specific compressive strength and modulus of W–PU foams increased by 55% and 48% with lignin content increasing from 0 to 20%, and the 20-day water absorption decreased by 38%. Thermal gravimetric analysis showed that the incorporation of lignin did not significantly affect the thermal degradation behaviour of foam, but it rather increased the mass of char residue. This study provides a promising method for value-added utilization of technical lignin in W–PU lightweight composites.
Highlights
Nowadays, density reduction has become a topical issue in wood-based composite industry for application in building and furniture [1,2,3]
Quantitative 31P nuclear magnetic resonance (NMR) analysis of lignin 31P NMR analysis was applied in order to quantitatively evaluate the content of OH groups in lignin
The content of OH groups is similar to the data in the literature for softwood kraft lignin, with total aliphatic and phenolic OH value of 4.89 mmol/g being reported [32]
Summary
Density reduction has become a topical issue in wood-based composite industry for application in building and furniture [1,2,3]. The lightweight wood-based panels are desirable for both economic and environmental reasons: lower costs in consequence of weight reduction and transportation, possibility of obtaining thick elements and ease of transportation and assembly [1, 4]. Rigid polyurethane (PU) foams are highly crosslinked, three-dimensional porous materials with many desirable properties such as low density, low thermal conductivity, As a hybrid lightweight composite, wood–polyurethane (W–PU) foam is usually produced through interaction between polyols and isocyanate with wood particles as the filler or reinforced component [10]. Incorporating wood into PU has many advantages.
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