Polymer blends based on PEO and starch: Miscibility and spherulite growth rate evaluated through DSC and optical microscopy

Adsorption and Structuration of PEG Thin Films: Influence of the Substrate Chemistry

This study investigates polyethylene glycol (PEG) homopolymer thin film adsorption on gold surfaces of controlled surface chemistry. The conformational states of physisorbed PEG are analyzed through polarization modulation infrared reflection-absorption spectrometry (PM-IRRAS). The PM-IRRAS principle is based on specific optical selection rules allowing the detection of surface-specific FTIR response of thin polymer films on the basis of differential reflectivity at the polymer/substrate interface for p- and s-polarized light. The intensification of the electric field generated at the PEG/substrate interface for p-polarized IR light in comparison with s-polarized light permits the analysis of PEG chain anisotropy and conformational changes induced by the adsorption. Results showed that PEG adsorbs on model substrates having a rather hydrophilic character in a way that the PEG chains spread parallel to the surface. In the case of a very hydrophilic substrate, the adsorbed PEG chains are in a stable thermodynamic state which allows them to arrange and crystallize as stacked crystalline lamellae after adsorption. The surface topography and morphology of the PEG thin films were also investigated by atomic force microscopy (AFM). While in the bulk state, PEG crystallizes in the form of large spherulites; on substrates whose adsorption is favored by surface chemistry, PEG crystallizes in the form of stacked lamellae with a thickness equal to 20 nm. Conversely, on a hydrophobic substrate, the PEG chains do not crystallize and adsorption occurs in the statistical coil state.

Improvement in Phase Compatibility and Mechanical Properties of Poly(L-lactide)-b-poly(ethylene glycol)-b-poly(L-lactide)/thermoplastic Starch Blends with Citric Acid

Flexible poly(L-lactide)-b-poly(ethylene glycol)-b-poly(L-lactide) block copolymer (PLLA-PEG-PLLA) bioplastic has been blended with low-cost thermoplastic starch (TPS) to prepare fully biodegradable bioplastics. However, the mechanical properties of PLLA-PEG-PLLA matrix decrease after the addition of TPS. In this work, citric acid (CA) was used as a compatibilizer to improve the phase compatibility and mechanical properties of PLLA-PEG-PLLA/TPS blends. TPS was first modified with CA (1.5 %wt, 3 %wt, and 4.5%wt) before melt blending with PLLA-PEG-PLLA. The PLLA-PEG-PLLA/modified TPS ratio was constant at 60/40 by weight. CA modification of TPS suppressed the crystallinity and enhanced the thermal stability of the PLLA-PEG-PLLA matrix, as determined through differential scanning calorimetry (DSC) and thermogravimetric analysis (TGA), respectively. The compatibility between the dispersed TPS and PLLA-PEG-PLLA phases was improved through modification of TPS with CA, as revealed by the smaller size of the co-continuous TPS phase from scanning electron microscopy (SEM) analysis. Increasing the hydrophilicity of the blends containing modified TPS confirmed the improvement in phase compatibility of the components. From the tensile test, the ultimate tensile strength, elongation at break, and Young's modulus of the blends increased with the CA content. In conclusion, CA showed a promising behavior in improving the phase compatibility and mechanical properties of PLLA-PEG-PLLA/TPS blends. These PLLA-PEG-PLLA/modified TPS blends have potential to be used as flexible bioplastic products.

Crystallinity of Amphiphilic PE-b-PEG Copolymers

The crystallinity and the growth rate of crystalline structures of polyethylene glycol and polyethylene blocks in polyethylene-b-polyethylene glycol diblock copolymers (PE-b-PEG) were evaluated and compared to polyethylene and polyethylene glycol homopolymers. Melting and crystallization behaviours of PE-b-PEG copolymers with different molecular weights and compositions are investigated by differential scanning calorimetry (DSC). The polyethylene/polyethylene glycol block ratio of the copolymers varies from 17/83 to 77/23 (weight/weight). The influence of the composition of PE-b-PEG copolymer on the ability of each block to crystallize has been determined. Thermal transition data are correlated with optical polarized microscopy, used to investigate the morphology and growth rate of crystals. The results show that the crystallization of the polyethylene block is closer to the polyethylene homopolymer when the copolymer contains more than 50 wt. % of polyethylene in the copolymer. For PE-b-PEG copolymers containing more than 50 wt. % of polyethylene glycol, the polyethylene glycol block morphology is almost similar to the PEG homopolymer. An important hindrance of each block on the crystallization growth rate of the other block has been revealed.

Improvement in Thermal Stability of Flexible Poly(L-lactide)-b-poly(ethylene glycol)-b-poly(L-lactide) Bioplastic by Blending with Native Cassava Starch

High-molecular-weight poly(L-lactide)-b-poly(ethylene glycol)-b-poly(L-lactide) triblock copolymer (PLLA-PEG-PLLA) is a promising candidate for use as a biodegradable bioplastic because of its high flexibility. However, the applications of PLLA-PEG-PLLA have been limited due to its high cost and poor thermal stability compared to PLLA. In this work, native cassava starch was blended to reduce the production cost and to improve the thermal stability of PLLA-PEG-PLLA. The starch interacted with PEG middle blocks to increase the thermal stability of the PLLA-PEG-PLLA matrix and to enhance phase adhesion between the PLLA-PEG-PLLA matrix and dispersed starch particles. Tensile stress and strain at break of PLLA-PEG-PLLA films decreased and the hydrophilicity increased as the starch content increased. However, all the PLLA-PEG-PLLA/starch films remained more flexible than the pure PLLA film, representing a promising candidate in biomedical, packaging and agricultural applications.

Effect of phosphonium based ionic liquid on structural, electrochemical and thermal behaviour of polymer poly(ethylene oxide) containing salt lithium bis(trifluoromethylsulfonyl)imide

Decrement in conductivity and flexibility of polymer electrolytes at higher ionic liquid concentration due to the crowding of anions.

Anticancer activity of starch/poly[N-(2-hydroxypropyl)methacrylamide]: biomaterial film to treat skin cancer

In the present work, films of pHPMA, pHPMAS hybrid, pHPMA-CPT and pHPMAS-CPT hybrid were prepared by solvent casting method and characterized by FT-IR, FT-Raman, XRD and DSC, respectively. The biocompatibility of the prepared pHPMA film and pHPMAS hybrid film were assessed using VERO cell lines and the percentage cell viability was found to be 97.4 and 98.3% for 7.8 μg/ml of the film extracts after 72 h of incubation. The cancer cell viability of the pHPMA-CPT film and pHPMAS-CPT film using MCF7 cell lines at pH 5.5 and 7.4 were found to be 4.9 and 8.6% and 7.7 and 12.3%, respectively. In vitro release of camptothecin from pHPMA-CPT and pHPMAS-CPT films in phosphate-buffered saline solution at pH 5.5 and 7.4 were monitored and analyzed using UV-vis spectrophotometer at λmax of 360 nm.

Starch-based microspheres for sustained-release of curcumin: preparation and cytotoxic effect on tumor cells

Curcumin (CUR) has been proved to be highly cytotoxic against different tumor cell lines. However, its poor solubility in aqueous medium and fast degradation in physiological pH are the common drawbacks preventing its efficient practical use. Herein, we report the development of original microspheres based on the biopolymer starch crosslinked with N,N-methylenebisacrylamide (MBA) to be applied as an efficient delivering system for CUR. The starch-based microspheres showed high loading efficiency even in loading solution with different CUR concentrations. In vitro release assays data showed that the CUR release is governed by anomalous transport (n=0.73) and it is pH-dependent. Cytotoxicity assays showed that starch microspheres could improve the cytotoxicity of CUR toward Caco-2 and HCT-116 tumor cell lines up to 40 times than that found for pure CUR. This behavior was attributed to the slowly and sustained release of CUR from the microspheres.

Electrospun PHBV/PEO co-solution blends: microstructure, thermal and mechanical properties

Blending allows to tailor and modulate the properties of selected polymers. Blends of poly (3-hydroxybutyrate-co-3-hydroxyvalerate) (PHBV) and polyethylene oxide (PEO) were fabricated by electrospinning in different weight ratios i.e. 100:0, 80:20, 70:30, 50:50, 0:100. In order to evaluate the influence of PEO addition on the final properties of PHBV, a complete microstructural, thermal and mechanical characterization of PHBV/PEO blends has been performed. The two neat polymeric membranes were also considered for the sake of comparison. The following characterization techniques were employed: scanning electron microscopy (SEM), X-ray diffraction analysis (XRD), Fourier transform infrared attenuated total reflectance (FTIR-ATR) spectroscopy, simultaneous thermogravimetric and differential analyses (TG-DTA), differential scanning calorimetry (DSC), and uniaxial tensile tests. All electrospun mats consisted of randomly oriented and uniform fibers. It has been observed that the microstructure of PHBV/PEO was remarkably affected by blend composition. The average fiber size ranged between 0.5 μm and 2.6 μm. It resulted that the electrospun polymeric blends consisted of separate crystalline domains associated to an amorphous interdisperse phase. PHBV/PEO blends presented intermediate mechanical properties, in terms of tensile modulus and ultimate tensile stress, with respect to the two neat components.