In this work Poly ε-caprolactone (PCL)/ Diglycidyl ether of bisphenol A (DGEBA) blends were electrospun and the obtained mats were UV cured to achieve shape memory properties. In the majority of studies, when blends with different compositions are electrospun, the process variables such as voltage or flow rate are fixed independently of the composition and consequently the quality of the fibers is not optimized in all of the range studied. In the present work, using the design of experiments methodology, flow rate and voltage required to obtain a stable process were evaluated as responses in addition to the fiber diameter and shape memory properties. The results showed that the solution concentration and amount of PCL played an important role in the voltage and flow rate. For the shape memory properties excellent values were achieved and no composition dependence was observed. In the case of fiber diameter, similar results to previous works were observed.
Epoxy/Polycaprolactone (PCL) blends cured with a conventional diamine (4,4′-diaminodiphenylmethane, DDM) and with different amounts of a disulfide containing diamine (4, 4´-dithioaniline, DSS) were prepared through melting. The curing process was studied by FTIR and differential scanning calorimetry (DSC) and the mechanical behavior of the networks was studied by DMA. The shape memory properties and the recyclability of the materials were also analyzed. All blends showed a very high curing degree and temperature activated shape memory effect, related to the glass transition of the epoxy resin. The PCL plasticized the mixture, allowing tailoring of the epoxy glass transition. In addition, in the blends cured with DSS, as a consequence of the disulfide exchange reaction, the permanent shape could be erased and a new shape could be reprogrammed. Using this strategy, reprogrammable permanent shape memory materials were obtained.
Films with shape-memory properties were obtained after photocuring blends of diglycidyl ether of bisphenol A (DGEBA) with previously crystallized poly(ε-caprolactone) (PCL). The effect of the epoxy photopolymerization on the semicrystalline PCL was studied, and transesterification reactions between epoxy and PCL were confirmed to occur in the amorphous regions of the DGEBA/PCL samples by Fourier transform infrared (FTIR) and gel content determination. Polarized light optical microscopy (PLOM) observations showed that because curing and transesterification reactions were confined to the amorphous regions of the sample, a spherulitic template was created with remarkable reversibility upon melting and recrystallization. To analyze the effect of this template on PCL crystallization, self-nucleation experiments were performed by differential scanning calorimetry (DSC). Within the spherulitic templates of photocured samples, in the amorphous regions, chains are confined near cross-linking points. The crystalline memory vanishes upon melting because the cross-link points induce an elastic entropy-driven response that changes the direction of chain orientation in the melt, as revealed by changes observed in the birefringence sign of the sample. The effect of the DGEBA/PCL composition on the shape-memory properties was analyzed, and better fixation was obtained at higher contents of epoxy resin. Instead, better recovery could be obtained for samples with higher amounts of PCL.
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