Shape fixity and shape recovery characteristics of aliphatic epoxy-benzoxazine shape memory polymer
Shape memory polymers (SMPs) are polymers that can fix the temporary shape and recover to the permanent shape by external stimuli. Epoxy resins are an important family of SMPs due to their excellent stability, thermomechanical endurance and the high values of shape fixity. However, epoxide ring opening polymerization required a curing agent which possesses some disadvantages such as high cost, toxic problem to the user and corrosion to the processing apparatus. In this research, novel series of SMPs were prepared from aliphatic epoxy as soft segment and benzoxazine resin (BA-a) as hard segment. Additionally, benzoxazine resin can also function as a curing agent for the epoxy. The composition of BA-a in BA-a/aliphatic-epoxy SMPs was controlled to be in the range of 30 to 50 mol%. Shape fixity and shape recovery as well as essential thermomechanical properties of the BA-a/aliphatic-epoxy SMPs were characterized by dynamic mechanical analysis (DMA) and shape memory test. The results revealed that storage modulus at room temperature of the obtained SMPs was increased from 2.8 GPa at BA-a content of 30 mol% to the value of 4.5 GPa at 50 mol% of BA-a. The glass transition temperature (Tg) obtained from the maximum peak of the Tan d was outstandingly increased with an increasing in BA-a content and reported to be in the range of 51 to 140 °C. The increment in Tg was also correspond to the raise in the crosslink density of BA-a-modified aliphatic epoxy SMPs. From the shape memory test, all SMP samples exhibited a high value of shape fixity close to 100%. Furthermore, the presence of BA-a content in BA-a/aliphatic epoxy SMPs imparted a greater in recovery stress ranging from 0.25 to 1.59 MPa or about 6 times improvement. These SMPs based on aliphatic epoxy-benzoxazine are highly attractive for shape memory materials to be used in a broader range of applications at elevated temperature and with greater recovery stress.
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