Poly (caprolactone/polylactic Acid/nanoparticle Composite Material Structure And Performance

Poly(ε-caprolactone)(PCL) and polylactide (PLA) are two typical biodegradable polymers with wide variety of the mechanical properties and biodegradability, and hence to blend them together is a simple way to obtain new biomaterials with excellent performance. However, the thermodynamic incompatibility between the two polymers leads to the formation of macroscopic phase separation structure in their blend. Thus, improving phase morphology is very important to improve performance of the PCL/PLA blend and to broaden its application areas. Besides the traditional approaches, adding rigid nanoparticles is also an effective way of improving the compatibility. But to make the morphology of blends design able and controllable in this case, the selective location of nanoparticles in the blends is very important.Therefore, in this work, the immiscible PCL/PLA blends with various component ratio and viscosity ratio were prepared by melt blending for rheology and morphology characterizations. The effects of interfacial tension and viscosity ratio on the phase morphology and inversion behavior were discussed. Then, the ternary systems filled with clay and carbon nanotubes were also prepared by melt blending under the same processing conditions, and the different selective location behaviors of clay and carbon nanotubes were explored. The phase morphology of PCL/PLA blends was then designed through the control of the selective location of two particles. The obtained results are as follows:(1) PCL/PLA blend is a typical immiscible blend. The interfacial tensions between the two components calculated according to rheology and surface contact angle measurements are in the same order of magnitude (1.0-2.5mN·m-1). The phase behavior of blends depends strongly on the viscosity ratio (ηPLA/ηPCL):the blends with the viscosity ratios of8.0,3.8and1.2show co-continuous phase structures in the phase inversion region. The phase inversion region of the blends is also dependent on the viscosity ratio:the phase of the blend with higher viscosity ratio inverses as the PCL content achieves to50wt%, while the phase of the blend with lower viscosity ratio inverses as the PCL content achieves to30wt%. Besides, the phase inversion point can not be well predicted using the viscosity models, because the elasticity is not taken into account in those models.(2) Due to thermodynamic and kinetic factors, clay and carbon nanotubes show different selective locations in the PCL/PLA blends:clay is mainly distributed in the PLA phase, while carbon nanotubes are mainly in the PCL phase. Thermodynamic factor is the dominant one resulting in the selective locations of the clay because the interfacial tension of the systems is reduced when the clay locates in the PLA phase. However, the location of carbon nanotubes in the PCL phase is contrary to the thermodynamical predictions, and changing the kinetic factors such as viscosity ratio, composition and processing conditions can not alter the their selective location in the PCL phase. This may be attributed to some unknown aspects.(3) The different selective location behaviors of clay and carbon nanotubes can be used to control and design the morphology of PCL/PLA blend:the blends with higher viscosity ratio and lower concentration of PLA becomes co-continuous when filled with clay. For the blends with "sea-island" structure, the addition of carbon nanotubes can make the size of the dispersed phase more uniform. For co-continuous blends, additior of the clay and carbon nanotubes change the phase structure to the "sea-island" one This is because the selectively located nano-particles change the mechanism of broker or coalescence of the dispersed phase. Furthermore, the phase morphology and the size of dispersed phase can be further controlled by the content of nano-particles.(4) The selective location of nanoparticles can affect crystallization behavior of PLA and PCL components in the ternary systems. For the melt crystallization behavior o PLA component, the clay located in the PLA phase has remarkable heterogeneous nucleation effect. But the crystallization rate of PLA more or less reduces. Both the clay and the carbon nanotubes located on the phase interface can promote the cold crystallization of PLA. For the crystallization behavior of PCL component, the carbon nanotubes located in the PCL phase have remarkable heterogeneous nucleation effect. But the presence of those carbon nanotubes also reduces the crystallization rate of PCL. The crystallization activation energy of PLA and PCL components depends on the selective locations of the nanoparticles:both the clay and the carbon nanotubes reduce crystallization activation energy of the PLA, while only the clay reduces crystallization activation energy of the PCL.