Eco-Friendly Polyurethane Reactive Hot-Melt Adhesive Derived from Poly(-caprolactone-co-lactic acid) Diols

Due to the exhaustion of fossil resources and the degradationofthe environment, there is an increasing utilization of eco-friendlymaterials as substitutes for petroleum-derived materials. In thiswork, a series of poly(& epsilon;-caprolactone-co-lacticacid) diols were synthesized via one-pot ring-opening polymerizationwith different lactic acid (LA)/& epsilon;-caprolactone (CL) feed ratios.Subsequently, the eco-friendly diols were mixed with polyether diol,4,4 & PRIME;-diphenylmethane diisocyanate (MDI), and other additivesto produce polyurethane reactive hot-melt adhesives (PURHAs). Theenhancement of LA/CL feed ratios correspondingly led to an increasein the glass transition temperature (T (g)) of the eco-friendly polyester diols. The differential scanningcalorimetry (DSC) data demonstrated that PCL-diol had the highestcrystallinity, and the polarizing optical microscopy (POM) observationsrevealed the smallest spherulite size in PCLA28-diol. Thermogravimetricanalysis (TGA) results indicated that the 5 wt % loss temperature(T-5) of PURHAs surpassed 265 & DEG;C. Tensile testing showedthat the elongation at break of PURHAs containing PCL segments increasedby at least eight times compared to PURHA without PCL segments. Lap-sheartesting illustrated that a PURHA with a higher LA/CL ratio exhibitshigher green strength. In addition, PUHRA-PCLA28 derived from PCLA28-dioland PUHRA-PCL derived from PCL-diol possessed better tensile and lap-shearstrengths. Notably, the lap-shear strengths of PUHRA-PCLA28 and PUHRA-PCLon a PC substrate reached impressive values of 8.85 and 8.05 MPa,respectively. These bio-based PURHAs synthesized from eco-friendlypolyester diols with different LA/CL ratios show potential applicationsin electronic appliances, the automotive industry, and constructionmaterials.