Shape memory polymers (SMPs) have been received a great deal of attention for decades. Due to the ability of shape changing under different conditions, it has been studied and developed with an expectation of wide potential applications. SMPs are stimuli-responsive materials, which are able to memorize a permanent shape. It is manipulated and fixed in intended temporary shape with an applied external force below a transition temperature, Ttrans. Some SMPs are generally known as suitable to be biologically decomposed such as polyurethane, polyesters, polyether urethane and their blends or block copolymers. Especially, PCL, semi-crystalline polyester, is noticeable biodegradable soft material for biomaterial applications. Even though its crystalline segments help to fix a temporary shape at low temperature, it has some limitations such as low durability, low strength and low stiffness, which put a limit on making enough recovery force. To overcome these problems, polymer blending can be an easily accessible way. Polyurethane has used for shape memory polymers because of their mechanical properties-flexibility and potentially biocompatibility. Jing et al. recently studied the blending of TPU and PCL as SMP for applying self-knotting sutures. As adjusting the weight ratio of two materials, they found the output of best shape memory effect. The similarity between the microstructure of PCL and a soft block of PU make them have high miscibility, however, it shows partially miscible from the reason of the differential molecular weight between them. It might be the main factor of a slow recovery in shape memory effect. Adding diisocyanate as compatibilizer might be the solution to improve the state of miscibility. The aim of this research is to find the best ratio of PLA/TPU blends, which shows high shape recovery and fixed deformation. And, the effect of diisocyanate as compatibilizer is investigated to improve the miscibility. The tests for shape memory effect are performed under the condition of 40~65℃ because it potentially applied to a human body, where the use of high temperature needs to be avoided. There is much difference of the melting points between TPU and PCL. When compounding is done at 200℃, PCL is already melted before putting into the compounder. PCL and TPU were blended with 1.4-phenylene diisocyanate (PDI) at different percentages of weight ratios. TPU content is arranged with 50, 70, 80, 90, 100 wt%, respectively. Each of blends has prepared in different ratio with the addition of PDI, 0, 1, 2, 3 wt%. Shape memory effects are investigated by means of the bending test method. Scanning electron microscopy (SEM) is performed to investigate the microstructure of the composites and see the miscibility. As the percentage of PCL is increased, the temporary shape is easily fixed. Blends included 50% are totally fixed at room temperature. However, these blends show relatively low shape recovery, which has decreased by approximately 20% compared to others included much lower PCL. In case of blends having the high percentage of PCL, Existence of PDI has an effect on increasing the shape recovery. Furthermore, PDI makes blends have high miscibility based on results of SEM. There was a definite change when PCL is included in blends. Comparison to pure TPU, blends are rightly fixed without external force after being programmed in the intended temporary shape. The ideal ratio of PCL/TPU is 30/70. According to the results of SEM, diisocyanate made to increase the compatibility of blends, in other words, it acted as compatibilizer and chain extenders as well.
Anahtar Kelimeler: Shape memory polymers, Poly ε-caporlactone, Thermoplastic polyurethane, diisocyanate
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