Bio-polyols synthesized from bio-based 1,3-propanediol and applications on polyurethane reactive hot melt adhesives

Since polyol is one of the major components in the preparation of polyurethane adhesive, bio-based polyols applied in the adhesive can make them sustainable and environmentally friendly. Regarding of these properties, a series of new bio-based aliphatic poly(1,3-propylene dicarboxylate) diols were synthesized by bio-based 1,3-propanediol (bio-PDO) and aliphatic dicarboxylic acids with different chain lengths. These bio-based polyester diols combined with 100% renewably-sourced poly(trimethylene ether) glycol (PO3G) further reacted with 4,4'-diphenylmethane diisocyanate (MDI) to form polyurethane reactive hot melt adhesives (PURHMAs). The thermal and physical properties of sustainable PURHMAs were characterized by differential scanning calorimetry (DSC), X-Ray diffraction (XRD), dynamic mechanical thermal analyzer (DMA) and thermogravimetric analysis (TGA). Finally, the adhesion properties of PURHMAs on four different substrates were measured, in order to investigate the influence of carbon numbers in the repeating unit of bio-based polyester diols on the morphology and adhesive properties of PURHMAs. It was found that with increasing carbon numbers in the repeating unit, the compatibility between the bio-based polyester and PO3G chains in the PURHMAs was enhanced, the open time of PURHMAs became shorter, and the green strength was also improved. The adhesion performance of bio-based PURHMAs on different substrates was tested, and the results showed that all bio-based PURHMAs had good adhesion to PC, nylon 6 and stainless steel substrates. Furthermore, the bio-based PURHMAs also exhibited excellent bonding strength on PC substrates after the bonded PC/PC joints were aged under the condition of hot water or alkaline solution. All these results suggests that the bio-based PURHMAs can be used in automobile applications.