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In this study, the effect of graphene nanoplatelets (GNPs) on the shape memory properties of poly(L-lactic acid) (PLLA) was studied. In addition to thermal activation, the possibility of infrared actuating of thermo-responsive shape mem- ory PLLA/GNPs nanocomposite was investigated. The incorporated GNPs were expected to absorb infrared wave's energy and activate shape memory PLLA/GNPs. Different techniques such as differential scanning calorimetry (DSC), wide-angle X-ray diffraction (WAXD), field emission gun scanning electron microscope (FEG-SEM) and dynamic mechanical thermal analysis (DMTA) were used to characterize samples. DSC and WAXD results indicated that GNPs augmented crystallinity due to nucleating effect of graphene particles. GNPs improved both thermal and infrared activating shape memory properties along with faster response. Pure shape memory PLLA was slightly responsive to infrared light and its infrared actuated shape recovery ratio was 86% which increased to more than 95% with loading of GNPs. Drastic improvement in the crystallinity was obtained in nanocomposites with lower GNPs contents (0.5 and 1 wt%) due to finer dispersion of graphene which resulted in more prominent mechanical and shape memory properties enhancement. Infrared activated shape memory PLLA/GNPs nanocomposites can be developed for wireless remote shape control of smart medical and bio-systems.

In this work, silane crosslinking of poly (lactic acid) (PLA) was studied. PLA was grafted with vinyl-trimethoxysilane (VTMO) via melt mixing in an internal mixer, followed by a crosslinking reaction in hot water for different times. The effect of simultaneous hydrolytic degradation in hot water (70°C) during crosslinking was monitored. Silane grafting of PLA was characterized using mixing torque and gel permeation chromatography (GPC) analysis. The results revealed that by increasing the silane (0–7 wt%) and peroxide (0–0.5 wt%) contents, the degree of grafting was increased. A peak corresponding to higher molecular weight in GPC chromatograms appeared in comparison to pure PLA due to the grafting reaction. Gel content, swelling test, GPC and thermal gravimetric analysis (TGA) were performed to monitor gel structure and concurrent hydrolytic degradation. Results confirmed that the occurrence of hydrolytic degradation during crosslinking and gel content of some samples tended to zero over 10 hr of immersion in hot water. The effect of hydrolytic degradation was not significant up to 10 hr and a tight gel structure was obtained. However, at longer crosslinking times, hydrolytic degradation was the dominant mechanism that leads to network defects.

In this work, basic mathematical models and response surface graphs have been used to illustrate the relationship between mixing parameters in internal mixer and properties of the SBR (styrene butadiene rubber)/organoclay composites. Using a Box-Behnken statistical design experiment methodology, the effects of mixing temperature (80-140°C), mixing time (4-12 min) and nano filler amount (3-9 phr) in SBR nanocomposites on the properties (tensile properties, scorch time and Mooney viscosity) were evaluated. It was found that the mixing parameters (time and temperature) have the predomi- nant role in properties and morphology of nanocomposite. The R 2 values (the R 2 values indicate the degree of agreement between the experimental results with those predicted by model) of all responses were above 0.85. Increasing temperature and mixing time facilitated a better organoclay dispersion which resulted in a better tensile property. With increase in nan- oclay amount in composite the scorch time and Mooney viscosity decreased. The morphology of nanocomposite was stud- ied by XRD (X-ray diffraction) and TEM (Transmission electron microscope). Intercalation and exfoliation of the nanoclay were observed for samples with higher temperature and longer mixing time. Due to thermal degradation of the rubber matrix at 140°C, tensile properties of the nanocomposite were decreased.