ABSTRACT
Characterizing the mechanical properties of polymer coatings typically requires access to specialty equipment, the analysis through which can be tedious despite instrumental precision. An alternative method reported in the literature,strain-induced elastic buckling instability for mechanical measurements (SIEBIMM), is a high throughput, facile yet accurate method, used to characterize the Young's modulus of supported films and coatings. SIEBIMM can easily be implemented in both academic and industrial settings. HYPOTHESIS: We hypothesize that the SIEBIMM method has an upper coating thickness limit beyond which the assumptions and practicality of the method are no longer valid. EXPERIMENTS: The Young's moduli of model polyvinyl alcohol coatings (on polydimethylsiloxanesubstrates) with thicknesses ranging from 67 nm to 40 µm were determined using the SIEBIMM method and the data were subjected to a rigorous statistical analysis. FINDINGS: SIEBIMM could accurately characterize coatings up to 35 µm thick. The Young's modulus of all coatings ≤ 35 µm was 1.6 ± 0.1 GPa at 50% RH, which agreed with free-standing polyvinyl alcohol films measured by traditional tensile testing. For the method to be used on thicker coatings, it is essential to consistently measure coating thickness and buckling wavelength at the same location to minimize potential error.
ABSTRACT
Paper was impregnated with neat polyvinyl alcohol (PVOH) or cellulose nanocrystal (CNC) reinforced PVOH, and dried by infrared radiation. Complex phenomena involved during paper impregnation and drying have been rarely investigated in the scientific literature, although these steps are crucial for the properties of the ensuing paper. The drying kinetics was studied and it showed that CNC tends to reduce the skin effect classically observed during fast PVOH drying. Furthermore, the nanoparticles induced faster water removal at the end of the drying step, which can be explained by an increase of the absorbed heat flux density. In addition, PVOH crystallization mechanisms have been studied through classical equations (Avrami, and Arrhenius) and a model (the Hoffman-Weeks method) and it was proved that both the drying conditions and the presence of CNC act on the crystallization of the polymer.
ABSTRACT
From a single plant source, a wide range of mechanically-deconstructed cellulose nanomaterials can be obtained due to the large number of possible combinations of pre-treatments, mechanical disintegration process, and post-treatments. It leads to the existence of a variety of cellulose nanofibrils with different shapes, morphologies, and properties on the market. The resulting material is actually a complex mixture of nanoscale particles, microfibrillated fibers, and residual fibers on the millimeter scale. Defining a "degree of fibrillation" for determining the final cellulose nanofibril quality is a challenging issue. This study proposes a multi-criteria method to obtain the quality index of cellulose nanofibril suspensions under the form of a unique quantitative grade. According to this method, the influence of different parameters such as pulp conditioning, refining, and hemicellulose content on the defibrillation process is highlighted. This method also allows for the benchmarking of different commercial nanocellulose products.
