Study On The Preparation And Properties Of One-Component Polyurethane Powder Adhesives

Traditional polyurethane adhesives are solvent-borne systems,which will release considerable toxic volatile organic compounds?VOC?in the process of production and use.Along with the establishment and the consummated of environmental legislation all over the world and people pay close attention to environment,the solvent-based polyurethane adhesives are being gradually replaced by the environment-friendly polyurethane adhesives.Polyurethane powder adhesives?PPA?have attracted great interest due to their excellent chemical properties,conveniently transport and low cost for use in many areas including the footwear industries,wood processing,packaging and so on.A new technology integrating the synthesis and granulation was adopted to prepare the one-component PPA by the solution polymerization.The polyurethane prepolymers were synthesized with polyethylene adipate diethylene glycol diol with a molecular weight of 3000?PDA3000?as soft segments,the diisocyanate?isophorone diisocyanate?IPDI?,hexamethylene diisocyanate?HDI??,1,4-butanediol?BDO?and dimethylolpropionic acid?DMPA?as hard segments.The influences of the ratio of soft to hard segment and types of dispersion solutions on the preparation of PPA were investigated.By the comparison,the prepolymers with the ratio of soft to hard segment of 3.0 had good dispersibility,the particle size of the the PPA was between100 and 180 mesh.In this method,based on the principle of solution polymerization,the mechanism of preparing PPA was discussed.Different poor solvents were selected by observing the polymer particle morphology,granulation process and adhesion properties.The liquid paraffin?A?could make the prepolymer to occur swelling so difficult for granulation.The polyurethane prepolymers had the remarkable phase separation in the self-made dispersion-liquid?D?.The initial T-peel strength of PPA prepared by self-made dispersion-liquid was 58.0 N.cm^-1,the final T-peel strength was 94.0 N.cm^-1,and the melting temperature was about 54⁵7oC.Moreover,the T_i,T_50%,and T_max of PPA were little difference.This indicated that the thermal stability of PPA between different solutions were no significant difference.The influences of neutralization and HDI/IPDI compound on the properties of PPA was investigated.Significant increased of the thermal stability were observed after the neutralization,and the T-peel strength increased.Additionally,when the molar ratio of HDI to IPDI was 1:1,it was found that the associative PPA had lower melting temperature and sizing temperature,the T-peel strength of the PPA was relatively high,the initial T-peel strength strength was 38.8N.cm^-1,and the final T-peel strength strength was 46.0 N.cm^-1.The influences of R_total on the properties of the PPA with neutralization were investigated by means of GPC,DSC,TG and so on.The results showed that with the increased of R_total,the molecular weight and the crystallinity of PPA were increased,the T-peel strength and the thermal stability of PPA were enhanced.Additionally,The initial melting temperature and sizing temperature of the PPA increased with increasing the R_total,the initial melting temperature of the PPA became instability.It indicated that the samples with the R_total was 1.01 to 1.17 had lower initial melting temperature and stable storage.The total results showed that the best conditions for preparing PPA were that the R_total was ranging from 1.17 to 1.30 with neutralization.The sizing temperature of PPA was in the range of 85¹00oC,the thermostability was high,the initial T-peel strength was in the range of 70.4¹04.0 N·cm^-1,and the final T-peel strength was in the range of 124.4¹63.2 N·cm^-1.Morover,they had better comprehensive performances,as compared with the PPA with the un-neutralized IPDI or the PPA with IPDI/HDI compounds,which were in the acceptable range for commercial adhesives(30⁴0 N·cm^-1).