Efficient Regulation of the Cross-Linking Structure in Polyurethane: Achieving Outstanding Processing and Mechanical Properties for a Wind Turbine Blade

Although epoxy resin has been extensively used in the field of wind turbine blades, polyurethane has attracted much attention in recent years, due to its potential value of better fatigue resistance, lower processing viscosity and higher strength than epoxy resin blades. Herein, we construct a dense cross-linking structure in polyurethane (PU) based on different amounts of hydroxypropyl methacrylate (HPMA) with low processing viscosity and excellent mechanical properties. By increasing the content of HPMA, the thermal stability of PU is enhanced, but the micro-morphology does not change significantly. When the content of HPMA is 50 g (in 200 g copolymer), the PU sample PH-50 exhibits a viscosity of 70 MPa·s and a gelation time of 120 min at 25 °C, which is sufficient to complete processes like pouring and filling. By post-curing the PH-50 at 80 °C for 2 h, the heat distortion temperature can reach 72 °C, indicating the increase of temperature resistance. The PU copolymers also have excellent mechanical and dynamic thermo-mechanical properties due to the cross-linking structure between PU chains and poly-HPMA chains. Additionally, the PU copolymer has excellent compatibility with various glass fiber fabrics (GFF), showing a good match in the vacuum infusion experiment and great properties in the mechanical test. By compounding PH-50 with GFF, the composite with high strength is easily prepared for a wind turbine blade in various positions. The tensile strengths of the composites are all over 1000 MPa in the 0° direction. Such composites are promising for the future development of wind turbine blades that meet the stringent requirements for outstanding processing and mechanical properties.

Real-time monitoring of the starch cross-linking with citric acid by chemorheological analysis

Cross-linking has been used as a strategy to improve the mechanical properties of starch films. However, the concentration of the cross-linking agent and the cure time and temperature determine the structure and properties of the modified starch. This article, for the first time, reports the chemorheological study of cross-linked starch films with citric acid (CA) through monitoring the storage modulus as a function of time G'(t). In this study, a CA concentration of 10 phr showed a pronounced increase of G'(t) during the cross-linking of starch, followed by a constant plateau. Analyses of infrared spectroscopy validated the result chemorheological. In addition, the mechanical properties showed a plasticizing effect of the CA at high concentrations. This research demonstrated that chemorheology is a valuable tool in the study of starch cross-linking, which becomes a promising technique to evaluate the cross-linking of other polysaccharides and cross-linking agents.

Increasing the Hydrophobic Component of Poloxamers and the Inclusion of Salt Extend the Release of Bupivacaine from Injectable In Situ Gels, While Common Polymer Additives Have Little Effect

Various strategies have been applied to reduce the initial burst of drug release and sustain release from poloxamer-based thermoresponsive gels. This work focussed on investigating different formulation approaches to minimise the initial burst of release and sustain the release of the small hydrophilic drug bupivacaine hydrochloride from poloxamer-based thermoresponsive gels. Various in situ gel formulations were prepared by varying the polypropylene oxide (PPO)/polyethylene oxide (PEO) ratio and by adding additives previously described in the literature. It was observed that increasing the PPO/PEO ratio from 0.28 to 0.30 reduced the initial burst release from 17.3% ± 1.8 to 9.1% ± 1.2 during the first six hours and extended the release profile from 10 to 14 days. Notably, the inclusion of sodium chloride (NaCl 0.4% w/w) further reduced the initial burst release to 1.8% ± 1.1 over the first 6 h. Meanwhile, physical blending with additive polymers had a negligible effect on the burst release and overall release profile. The findings suggest that extended release of bupivacaine hydrochloride, with reduced initial burst release, can be achieved simply by increasing the PPO/PEO ratio and the inclusion of NaCl.

Injectable thermoresponsive gels offer sustained dual release of bupivacaine hydrochloride and ketorolac tromethamine for up to two weeks

Bupivacaine and ketorolac are commonly used in combination to reduce perioperative pain. This study aimed to develop and characterize an injectable system that offers simultaneous and prolonged release of bupivacaine and ketorolac. Formulations were prepared using poloxamer 407 with increasing concentrations of poloxamer 188 and sodium chloride. Small Angle X-ray Scattering (SAXS) experiments demonstrated that the poloxamers form gels with a cubic lattice arrangement regardless of the matrix composition, whereas the system porosity is driven by poloxamers concentration. Drug loading slightly reduced the intermicellar spacing. Fourier transform infrared spectroscopy and thermal analysis suggested electrostatic interactions between the loaded drugs and poloxamers. Mechanical and rheological studies confirmed the formulations exhibit Newtonian-like flow at room temperature followed by a transition to a viscous gel at body temperature. Importantly, the developed formulations demonstrated steady and sustained release of both bupivacaine and ketorolac over two weeks. Sodium chloride reduced the initial burst release over the first six hours for BH, from 8.6 ± 0.18% to 1.6 ± 0.11%, and KT, from 7.7 ± 0.27% to 1.5 ± 0.10%. Hence, poloxamer-based thermoresponsive gelling systems are promising delivery platforms for the sustained delivery of bupivacaine and ketorolac, with potential clinical benefits for managing perioperative pain.