Preparation And Properties Of The Acrylic Structural Adhesives Initiated By Organborane

Low surface energy plastics are the most widely used plastics with excellent properties.Due to their low energy surface,these materials demonstrate poor interfacial adhesion.In order to improve the adhesion performances,many surface pretreatment methods have been employed.However,most of them are environmental unfriendly,expensive and complex.Therefore,it is badly in need of adhesive for bonding low surface energy materials without surface pretreatment.The acrylic structural adhesive for bonding low-surface-energy substrate without pretreatment was investigated in this project.First,in order to improve the poor adhesion to Polyethylene terephthalate(PET)substrate by common acrylic structural adhesive,acrylic adhesive initiated by tributylborane,which was a low temperature initiator,was prepared and the mechanism of adhesion to PET was researched.It was founded that acrylic adhesive was grafted onto the surface of PET substrate and its resulted shear strength was 4.89 MPa,while the other three acrylic structural adhesives initiated respectively by three different initiators had weak adhesion to PET substrate.Next,three paths of improving the toughness of adhesive were studied,including copolymerizing with soft monomer,blending with elastomer and copolymerizing with oligomer.What's more,the relationship between the adhesion strength and adhesion force,bulk strength and toughness of adhesive were explained.The lap shear strength of adhesive toughened by the tailored oligomer,which was consisted of silicone backbone and terminated by vinyl aromatic compound,was up to 11.05 MPa(the reported max shear strength of acrylic structural adhesive to PET substrate was only 6.95 MPa).The T-peel strength of adhesive was up to 5340 N/m,which was conformed to the requirements of application.It showed that the oligomer modified by silicone enhance the bonding strength by improving wettability,increasing crosslink degree and introducing soft chains.At last,the adhesion strength to Polypropylene(PP)together with the curing behavior of acrylic structural adhesive initiated by organborane,which included the effects of adhesive's component on its shrinkage and the mechanism and method of increasing the work life of the adhesive,were investigated.A low shrinkage was achieved by the addition of copper dibromide and acetoacetoxy ethyl 2-methylacrylate without any loss of adhesion strength.It was also founded that the work life was decided by the period of inhibition.The work life was lengthened from 1 min to 15 min as a result of the addition of copper dibromide,which also increased the rate of strength build to satisfy the assembly process.The another effect of addition of copper dibromide was that a homogenous structure of adhesive resulted from the homogenous curing speed was achieved and the resulted adhesion strength was improved slightly.