Preparation And Characterization Of Boiling Resistant Polyurethane (LPU) Adhesive For Film Laminate

Flexible packaging bags have the advantages of high strength,good air-tightness,waterproof,heat sealing etc.Therefore,they are extremely applied in the food packaging industry.The packaging quality not only relates with the laminated films properties,but also depends on adhesive performance.Two-component polyurethane adhesives play important role in food packaging industry because of the excellent comprehensive performance.Using aliphatic,aromatic acid,diethylene glycol and glycol as raw materials,polyester polyols were prepared via polyesterification and polycondensation.Polyester polyols and extender chain agent were mixed,and then,curing agent was added to the mixture to synthesize LPU adhesives.Comparing this polyurethane adhesive with overseas production,their resistance to boiling is similar.The mainly researches of this thesis are as follows:1.Using aliphatic,aromatic acid,diethylene glycol and glycol as raw materials,the series products of polyester polyols were prepared via polyesterification and polycondensation.The influences of reaction conditions,such as the molar ratio of alcohol and acid,the kinds of catalyst,the catalyst dosage were investigated.SnCl₂·2H₂O was adopted as catalyst,with a quality score of 0.03%.2.Polyester polyols,extender chain agent and curing agent were used to synthesize polyurethane adhesives.Changing the composition of polyester polyols,the ratio of aromatic and aliphatic acid and the molecular weight of polyesters to research the properties of LPU adhesives.And then,peel strength of polyurethane adhesive under room temperature and high-temperature boiling condition were discussed.TGA test showed that with the increase of the proportion of phenyl rings,the decomposition temperature and decomposition activation energy of polyurethane adhesives are improved.The DMA test showed that with the increase of the content of phenyl rings,the heat resistant was improved,as well as the good rigidity and resistance to deformation were maintained.3.The rheology of aromatic polyesters and their LPU adhesives were studied.Because of the low molecular weights,the apparent viscosity of polyester polyols solution was reduced rapidly with the increase of shear rate.So the polyester polyol solutions were good for coating process.With the increase of terephthalic acid,the apparent viscosity of LPU adhesives solution was reduced under low shear rate.But the apparent viscosity increased while under high shear rate,when the proportion of adipic acid was more than 50%.4.FT-IR test showed that the hydrogen bonds in LPU adhesives were disintegrated during the rise of temperature.That's because of the activation of the polyurethane adhesive molecules.Due to the existence of phenyl rings,the molecular chains are rigid.A higher temperature is required to activate the H-bonds.On the other hand,phenyl rings in the soft segments of polyurethane are joined with the hard segments,which increase the degree of hydrogen bond,hinder disintegration of the polyurethane adhesive and keep the physical properties at a wide range of temperature.5.Enlarged the experiment for actual production.The experiments for actual production were enlarged.The influence of COOH/OH ratio,reaction temperature and vacuum degree on the properties of polyester polyols was discussed.Then,the effects of NCO/OH ratio,curing process conditions on the LPU adhesives werevdiscussed.Finally,the optimized adhesive was compared with D-502.Their resistances to boiling resistant performance were similar.