Dissipative properties of composite structures. 1. Statement of problem

Object and purpose of research. The object under study is a sandwich plate with two rigid anisotropic layers and a filler of soft isotropic viscoelastic polymer. Each rigid layer is an anisotropic structure formed by a finite number of orthotropic viscoelastic composite plies of arbitrary orientation. The purpose is to develop a mathematical model of sandwich plate. Materials and methods. The mathematical model of sandwich plate decaying oscillations is based on Hamilton variational principle, Bolotin’s theory of multilayer structures, improved theory of the first order plates (Reissner-Mindlin theory), complex modulus model and principle of elastic-viscoelastic correspondence in the linear theory of viscoelasticity. In description of physical relations for rigid layers the effects of oscillation frequencies and ambient temperature are considered as negligible, while for the soft viscoelastic polymer layer the temperaturefrequency relation of elastic-dissipative characteristics are taken into account based on experimentally obtained generalized curves. Main results. Minimization of the Hamilton functional makes it possible to reduce the problem of decaying oscillations of anisotropic sandwich plate to the algebraic problem of complex eigenvalues. As a specific case of the general problem, the equations of decaying longitudinal and transversal oscillations are obtained for the globally orthotropic sandwich rod by neglecting deformations of middle surfaces of rigid layers in one of the sandwich plate rigid layer axes directions. Conclusions. The paper will be followed by description of a numerical method used to solve the problem of decaying oscillations of anisotropic sandwich plate, estimations of its convergence and reliability are given, as well as the results of numerical experiments are presented.

Bioinspired Thermo-Responsive Xyloglucan-Cellulose Nanocrystal Hydrogels

Thermo-responsive hydrogels present unique properties, such as tunable mechanical performance or changes in volume, which make them attractive for applications including wound healing dressings, drug delivery vehicles, and implants, among others. This work reports the implementation of bio-based thermo-responsive hydrogels comprised of xyloglucan (XG) and cellulose nanocrystals (CNCs). Thermo-responsive properties were obtained by enzymatic degalactosylation of tamarind seed XG (DG-XG), which reduced the galactose residue content by ~50%, and imparted a reversible thermal transition. XG with comparable molar mass to DG-XG was achieved by ultrasonication treatment (XGu) for direct comparison of behavior. The hydrogels were prepared by simple mixing of DG-XG or XGu with CNCs in water. Phase diagrams were established to identify the ratios of DG-XG or XGu to CNCs (from 1:300 to 20:1 by mass) that yielded a viscous liquid, a phase separated mixture, a simple gel, or a thermo-responsive gel. Gelation occurred at a DG-XG or XGu to CNC ratio higher than that needed for the full surface coverage of CNCs, and required relatively high overall concentrations of both components (tested concentrations up to 20 g/L XG and 30 g/L CNCs). This is likely a result of the increase in effective hydrodynamic volume of CNCs due to the formation of XG-CNC complexes. Investigation of the adsorption behavior indicated that DG-XG formed a more rigid layer on CNCs compared to XGu. Rheological properties of the hydrogels were characterized and a reversible thermal transition was found for DG-XG/CNC gels at 35°C, where the mechanical properties of the gel could be tuned by adjusting the CNC content

Bioinspired Thermo-Responsive Xyloglucan-Cellulose Nanocrystal Hydrogels

Thermo-responsive hydrogels present unique properties, such as tunable mechanical performance or changes in volume, which make them attractive for applications including wound healing dressings, drug delivery vehicles, and implants, among others. This work reports the implementation of bio-based thermo-responsive hydrogels comprised of xyloglucan (XG) and cellulose nanocrystals (CNCs). Thermo-responsive properties were obtained by enzymatic degalactosylation of tamarind seed XG (DG-XG), which reduced the galactose residue content by ~50%, and imparted a reversible thermal transition. XG with comparable molar mass to DG-XG was achieved by ultrasonication treatment (XGu) for direct comparison of behavior. The hydrogels were prepared by simple mixing of DG-XG or XGu with CNCs in water. Phase diagrams were established to identify the ratios of DG-XG or XGu to CNCs (from 1:300 to 20:1 by mass) that yielded a viscous liquid, a phase separated mixture, a simple gel, or a thermo-responsive gel. Gelation occurred at a DG-XG or XGu to CNC ratio higher than that needed for the full surface coverage of CNCs, and required relatively high overall concentrations of both components (tested concentrations up to 20 g/L XG and 30 g/L CNCs). This is likely a result of the increase in effective hydrodynamic volume of CNCs due to the formation of XG-CNC complexes. Investigation of the adsorption behavior indicated that DG-XG formed a more rigid layer on CNCs compared to XGu. Rheological properties of the hydrogels were characterized and a reversible thermal transition was found for DG-XG/CNC gels at 35°C, where the mechanical properties of the gel could be tuned by adjusting the CNC content