One-component Reactive Polyurethane Hot Melt Adhesive Preparation And Performance

In this paper, a series of isocyanate-terminated moisture-curable polyurethane hot-melt adhesives are prepared using prepolymer process with polytetramethylene glycol (PTMG, Mn = 2000) Polybutanediol adipate (PBA, Mn = 2000). polypropyleneoxy glycol (PPG, Mn = 2000) as soft segment, diphenylmethane-4, 4'-diisocyanate (MDI).. tolyene diisocyanate (TDI) as hard segment and 1,4-butanediol.. ethylene glycol.. diethylene glycol as chain extender. In addition to their high curing rate and adhesion strength, this type of hot-melts are solvent-free and recognized to be environmentally-friendly materials.The factors of reaction such as temperature.. time and speed of agitator are studied throuh monitoring the changes of special groups by means of chemical titration and infrared spectroscopy, and the optimum process conditions are determined. Meanwhile, the lap-shear strength and curing time of hot-melts with different isocyanate content.. isocyanate index (NCOIOH ratio).. hard and soft segment structure.. chain extender and catalyst for cure are measured respectively. And the effect of soft segment structure on initial adhesion serength.. crystallinity.. water resistance and heat resistance are investigated.The results show that low temperature inadequate time and slow speed of agitator result in an incomplete reaction and the presence of unreacted polymer polyols has a detrimental effect on curation and adhesion strength of hot-melts. Nevertheless, if the temperature is too higher and the speed of agitator too faster, the reaction system will gelate. Suitable conditions are given as follows:Temperature in both stages of prepolymerization and chain-extending is 75—-85℃; Time of prepolymerization is 1 hour with PlMG and PBA as soft segment and 3 hours with PPG as soft segment; Time of chain-extending is I 5—20min; speed of agitator is about 750r/min.The tests for adhesion properties of varied hot-melts tell that hot-melt with MDI as hard segment.. PTMG as soft segment.. l,4-butanediol as chain-extender..a mixture of dibutyltin dilaurate and triethylenediamine as catalyst.. NCO/OH ratio being 3.0:1 and isocyanate content being 1% has better adhesion properties, which provides adhesion strength up to about 6.74 MPa.