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Nonwoven fibrous mats based on semicrystalline networks are prepared starting from poly(ε-caprolactone) and properly combining electrospinning and sol-gel reactions. The mats are obtained as continuous, randomly oriented micrometric fibers with different network densities. The systems are subjected to thermomechanical cycles to investigate their one-way and two-way shape memory behavior. One-way tests aim at exploring the effects of the deformation temperature on the materials response, with particular interest to the less investigated cold-working conditions (i.e., deformation temperature below Tm). The materials display two-way shape memory capabilities (i.e., the ability to change between two distinguished shapes upon heating and cooling under a fixed nonzero stress) and the effect of the applied stress is explored. The shape memory characterization is accompanied by an ex situ SEM analysis, to describe the concurrent microstructural evolution during the macroscopic shape variation, and by the assessment of their biocompatibility, to explore the suitability of the nonwovens for biomedical applications. [ABSTRACT FROM AUTHOR]

The two-way shape memory behaviour of semicrystalline networks was investigated on systems based on poly(ε-caprolactone) featuring significantly different network architecture. Crosslinked poly(ε-caprolactone)s were prepared by thermal curing from methacrylic end-capped linear chains having various methacrylation degrees. By conveniently reducing the methacrylation degree, the crosslink density of cured materials was varied over a range of one order of magnitude, leading to comparable changes in the material compliance in the rubbery region, but only to moderate variations in melting and crystallization temperatures (Tm and Tc) and in the crystallinity content. When subjected to constant non-zero stress and to cooling–heating cycles from above Tm to below Tc, the materials undergo a reversible two-way elongation–contraction effect, whose extent depends on material structure and applied stress. The structural changes in the crystalline phase accompanying the cooling-induced elongation were studied through differential scanning calorimetry and X-ray diffraction analyses. The elongation process involves different contributions of entropy- and crystallization-driven processes, whose amounts were investigated as a function of the loading conditions and the molecular architecture. The role of the network density towards a controlled two-way response is evidenced, showing that a proper value of the crosslink density has to be identified to maximize the two-way elongation capabilities. [ABSTRACT FROM AUTHOR]

EPDM rubber was reinforced with titania in situ generated by using a nonhydrolytic sol-gel (NHSG) process starting from TiCl4 as titania precursor and tert-butanol as oxygen donor. Titania particles in anatase form and with average diameter of 6 nm were synthesized via NHSG route and then the same procedure was adopted in presence of EPDM rubber to obtain composites containing up to 30 wt% of filler. Extraction and equilibrium swelling tests suggested an interfering effect of the NHSG reaction on the vulcanization process of the rubber resulting to a crosslink density which decreased in the presence of titania. Quasi-static and dynamic-mechanical characterizations indicated that the presence of titania as rigid filler in both the unvulcanized and vulcanized EPDM matrix led to a significant increase in stiffness and stress at break. The experimental values of modulus were systematically higher than the values predicted by classical equations suggesting an additional stiffening contribution deriving from the molecular interaction between the rubber and the filler. POLYM. ENG. SCI., 54:2544-2552, 2014. © 2013 Society of Plastics Engineers [ABSTRACT FROM AUTHOR]

This work aimed at developing a thin and water-resistant food-grade poly(vinyl alcohol) (PVOH)-based matrix able to swell when in contact with high moisture content food products without rupturing to release antimicrobial agents onto the food surface. This film was prepared by blending PVOH and 7.20% (wt/wt of PVOH) of poly(ethylene glycol) (PEG) with citric acid as crosslinking agent. The film-forming solution was then casted onto a flat surface and the obtained film was 60 μm in thickness and showed a good transparency (close to T = 100%) in the visible region (400 to 700 nm). After immersion in water for 72 h at room temperature, the crosslinked matrix loses only 19.2% of its original weight (the percentage includes the amount of unreacted crosslinking agent, antimicrobial in itself). Water content, degree of swelling, and crosslinking density of the film prove that the presence of PEG diminishes the hydrophilic behavior of the material. Also the mechanical properties of the wet and dry film were assessed. Alongside this, 2.5% (wt/wt of dry film) of grapefruit seed extract (GSE), an antimicrobial agent, was added to the film-forming solution just before casting and the ability of the plastic matrix to release the additive was then evaluated in vitro against 2 GSE-susceptible microorganisms, Salmonella enteritidis and Listeria innocua. The results indicate that the developed matrix may be a promising food-grade material for the incorporation of active substances. [ABSTRACT FROM AUTHOR]

A series of novel Si-O-Si crosslinked organic/inorganic hybrid semi-crystalline polymers with shape memory properties was prepared from alkoxysilane-terminated poly(butylene succinate) (PBS) by water-induced silane crosslinking under organic solvent-free and catalyst-free conditions. The hydrolyzation and condensation of alkoxysilane end groups allowed for the generation of silica-like crosslinking points between the polymeric chains, acting not only as chemical net-points, but also as inorganic filler for a reinforcement effect. The resulting networks were characterized using differential scanning calorimetry (DSC), thermogravimetric analysis (TGA), dynamic-mechanical analysis (DMA) and tensile and shape memory tests to gain insight into the relationship between the polymeric structure, the morphology and the properties. By controlling the molecular weight of the PBS precursor, a fine tuning of the crosslinking density and the inorganic content of the resulting network was possible, leading to different thermal, mechanical and shape memory properties. Thanks to their suitable morphology consisting of crystalline domains, which represent the molecular switches between the temporary and permanent shapes, and chemical net-points, which permit the shape recovery, the synthesized materials showed good shape memory characteristics, being able to fix a significant portion of the applied strain in a temporary shape and to restore their original shape above their melting temperature. [ABSTRACT FROM AUTHOR]