| Thermoplastic polyurethane hot melt adhesive (PUHMA) was prepared used polyether/polyester polyol as soft segments, diisocyanate and chain extender as hard segments. Firstly, synthesis process of polyurethane hot melt adhesive was studied. The relationship between structure and properties of PUHMA was characterized by infrared spectrum (IR) and differential thermal analysis (DSC), thermogravimetry (TGA) and other test methods. Effects of the isocyanate index (R), the structure of hard and soft segments and chain extender on physical properties and bond properties of PUHMA were explored. Finally, the effect of different types of thermoplastic resin on performances of PUHMA was analyzed. To improve water resistance and heat resistance of polyurethane hot melt adhesive, PUHMA was modified by hydroxyl silicone oil and nano-SiO2respectively. The structure of polyurethane (PU) modified by hydroxyl silicone oil was characterized by infrared spectroscopy (IR). The effect of the content of hydroxyl silicone oil and nano-SiO2on water resistance, heat resistance and bonding properties were analyzed respectively. The membrane surface by scanning electron microscopy (SEM) was observed, and the distribution of nano-SiO2in the resin matrix was studied. The impact of the hydroxyl silicone oil and nano-SiO2on thermal performance of PUHMA was discussed by TGA tests. All experimental results were as follows:1. The optimum conditions thermoplastic polyurethane hot melt adhesive was confirmed that the synthesis temperature of PU prepolymer was controlled at80±5℃for2.5h. Then PU prepolymer was chain extended, and aged at110℃for4h, lastly. The physical properties and bonding properties of PUHMA were better when the isocyanate index was0.98-1.02and the amount of chain extender was1.0(molar ratio of polyester polyol and chain extender). The bonding strength of PUHMA based on polyester polyols was stronger, while the structure more regular and crystallinity stronger of polyols, the bonding strength of PUHMA stronger. The TGA test results showed that the thermal stability of PUHMA extended by different chain extender was ethylene glycol, butanediol, diethylene glycol in the order. Considered to be compatibilty, the type of thermoplastic resin was chosed to be thermoplastic polyurethane (TPU), it can improve polyurethane hot melt adhesive film, shorten the opening time, and increase bonding strength, the content was controlled to be about25wt%.2. PU modified by hydroxyl terminated polydimethylsiloxane (referred to be hydroxyl silicone oil) was prepared used polyester diol (PBA) and diphenyl methane diisocyanate (MDI) and1,4-butanediol as main raw materials by bulk polymerization. IR tests showed that the hydroxyl silicone oil successfully was embedded in the polyurethane molecular chain. The water resistance of modified polyurethane improved, when molar ratio of the polyester polyol and hydroxyl silicone oil was6:1, the surface water contact angle of polyurethane membrane enhanced about20℃, while bonding strength of modified polyurethane only drop0.16N/mm, decreased less than that of pure polyurethane. The TGA results showed that when the silicon-oxygen was introduced into PU main chain, the thermal decomposition rate of PU slowed down, and the second thermal decomposition of PU improved by30℃.3. The bonding strength and water resistance of PUHMA modified by nano-SiO2improved. When the content of nano-SiO2(HL-150) was1.0wt%, the bonding strength of polyurethane hot melt adhesive reached maximum,2N/mm, increased by about2times than that of pure polyurethane material, while modified PU presented good water resistance and low water absorption. With specific surface area of nano-SiO2increased, nano particles tended to agglomerate by SEM tests, at the condition of the same content; In this study, nano-SiO2was determined to be specific surface area of150m2/g. |
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