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A series of polyurethane (PU)/clay nanocomposite films was prepared by adding natural bentonite Cloisite ® Na + powders to waterborne polyurethane dispersions (PUDs) followed by a slow water evaporation; the nanoclay content in the films varied from 0 to 5 wt%. The functional properties of materials with low nanoclay loading (up to 1 wt%) resemble features of films prepared without any nanoclay. Compared to unfilled PU, the films with 3 and 5 wt% nanoclay concentrations exhibited slightly deteriorated properties. This phenomenon can be caused by the fact that the polymer-filler interactions are negligible. Gas transport properties are the exception: nanoclay was found to be an efficient barrier component for the permeability of industrially important gases (O 2 , N 2 , H 2 , CO 2 , and CH 4 ). All films feature thermoplastic characteristics and thermal stabilities up to at least 200 C. Because PUDs are solely composed of linear chains, the possibility of preparing recyclable materials was tested. While PU can be re-used after dissolving in acetone and re-dispersing in water, the re-use of nanoclay is not recommended. Preliminary accelerated in vivo tests performed in 20% H 2 O 2 and 0.1M CoCl 2 at 37 C detected substantial susceptibility to biodegradation, especially for films containing 5 wt% nanoclay. POLYM. COMPOS., 40:4079-4092, 2019.

Biodegradable thermoplastic starch (TPS) composites with isometric titanium dioxide nanoparticles (TiO 2 ; diameter ∼100 nm) and elongated titanate nanotubes (TiNT; diameter ∼20 nm and aspect ratio >50) were prepared from wheat and tapioca starch. The preparation was based on our recently developed two-step procedure consisting of the solution casting (SC) followed by the melt mixing (MM), which had been shown to yield highly homogeneous TPS in our previous study. In this work we demonstrated that the type of the TPS matrix and the type of the filler had significant impact on the morphology and the properties of the final composites. Multiple microscopic techniques (LM, SEM, and TEM) evidenced that the TPS/TiO 2 composites exhibited a very homogeneous dispersion of the filler, while the TPS/TiNT composites contained micrometer-size agglomerates of TiNT. Moreover, all composites with the wheat starch matrix [TPS(w)] showed a higher filler agglomeration than the corresponding composites with the tapioca starch matrix [TPS(t)]. Rheological experiments showed that the TiO 2 and TiNT fillers had quite small impact on the viscosity of the TPS(w) matrix, probably due to slightly higher agglomeration, poorer dispersion, and weaker matrix-particle interactions. On the other hand, the TPS(t) matrix was influenced by both fillers significantly: the TiO 2 nanoparticles with almost ideal dispersion formed a physical network in the TPS(t) matrix, which significantly increased the viscosity of the composite, whereas the TiNT nanotubes seemed to destruct the TPS(t) matrix partially, resulting in decreased viscosity of the composite. DMTA results confirmed the rheological measurements: Storage moduli (G') showed that TPS(t) and its composites with TiO 2 were stiffer than the corresponding TPS(w) samples, while the TPS(t)/TiNT composites were less stiff than TPS(w)/TiNT. Also loss moduli (G") confirmed the difference between tapioca starch and wheat starch composites, which differed by their glass transition temperatures [T g of TPS(w) < T g of TPS(t)]. The rheological and DMTA results were supplemented and supported by IR, XRD, and TGA measurements.

Biodegradable composites of thermoplastic starch (TPS), titanium dioxide particles (TiO 2 ; average size 0.2 µm), and/or antibiotic (ATB; vancomycin) were prepared. Light and electron microscopy demonstrated that our recently developed, two-step preparation procedure yielded highly homogeneous TPS matrix with well-dispersed TiO 2 particles even for high filler concentrations (up to 20%). Oscillatory shear rheometry showed an increase in viscosity of TPS after addition of TiO 2 and ATB (from ca 2 × 10 5 Pa·s to ca 1 × 10 6 Pa·s at 1 rad/s and 120 • C). However, the high viscosity of TPS/TiO 2 /ATB composites did not prevent reproducible preparation of the composites by melt-mixing. Dynamic mechanical analysis proved a significant increase in shear moduli (storage, loss and complex modulus) of TPS after addition of TiO 2 and ATB (storage modulus increased from ca 25 MPa to more than 600 MPa at 1.33 rad/s at room temperature). Both rheological and mechanical properties indicated strong interactions among TPS matrix, filler, and antibiotics. The final TPS composites were soft enough to be cut with a sharp blade at room temperature, the TPS matrix was fully biodegradable, the TiO 2 filler was biocompatible, and the ATB could be released locally during the matrix degradation. Selected samples were tested for bacterial susceptibility using standard tube dilution test and disk diffusion test. The results proved that the ATB retained its bacteriostatic properties after the thermal processing of the composites. Therefore, the prepared TPS/TiO 2 /ATB composites represent a promising material for biomedical applications related to the local release of antibiotics.

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