The influence of additives on polymer matrix mobility and the glass transition

Evaluation of Starch-Garlic Husk Polymeric Composites through Mechanical, Thermal, and Thermo-Mechanical Tests

The present work evaluates the influence of different properties of composite materials from natural sources. Films were prepared using the evaporative casting technique from corn starch reinforced with a waste material such as garlic husk (GH), using glycerin as a plasticizer. The results of the syntheses carried out demonstrated the synergy between these materials. In the morphological analysis, the compatibility and adequate dispersion of the reinforcer in the matrix were confirmed. Using Fourier transform infrared spectroscopy (FTIR), the interaction and formation of bonds between the matrix and the reinforcer were confirmed by the presence of some signals such as S-S and C-S. Similarly, thermogravimetric analysis (TGA) revealed that even at low concentrations, GH can slightly increase the decomposition temperature. Finally, from the results of dynamic mechanical analysis (DMA), it was possible to identify that the storage modulus increases significantly, up to 115%, compared to pure starch, especially at low concentrations of the reinforcer.

Understanding the balance between additives' miscibility and plasticisation effect in polymer composites: a computational study

Plasticisers are small organic molecules routinely added to polymer composites that modify the processability of the compounds by adsorbing on the filler's surface or dispersing into the polymer matrix. Here using a simple yet chemically specific coarse-grained model, we demonstrate that the filler surface coverage and the degree of dispersion into the polymer matrix can be tuned without modifying the chemistry of the plasticisers but only by varying their conformational flexibility. We show that when the adsorption mechanism and clustering into the bulk are entropically driven as in this work, this is a general phenomenon independent on the polymer chemistry and its molecular weight. Our findings suggest a simple practical design rule that requires only minor modifications of the plasticisers' chemistry to achieve maximum adsorption onto the filler surface or dispersion into the polymer matrix.

Sustainable Basalt Fibers vs. Traditional Glass Fibers: Comparative Study on Thermal Properties and Flow Behavior of Polyamide 66-Based Composites

In this work, basalt fibers (BF) have been investigated as possible natural and sustainable replacements for the common synthetic mineral filler—glass fibers (GF)—used in polyamide 66 matrix (PA66). Composites have been prepared at two different fiber concentrations (15 and 25 wt.%, respectively) by melt blending. The developed systems have been mainly characterized by thermogravimetric analysis (TGA), differential scanning calorimetry (DSC), capillary rheology, and scanning electron microscopy (SEM). The kinetic parameters to thermal degradation through the Coats–Redfern method allowed us to attest a negligible effect of fiber type on thermal stability of the developed systems. Composites incorporating 15 wt.% of fiber content possessed the highest activation energy (≥230 kJ/mol). The introduction of BF and GF in PA 66 polymer, regardless of content, always led to an increase in crystallization and melting temperatures, and to a similar reduction in crystallinity degree and glass transition temperature. The shear viscosity of the basic polymer increased by the addition of fillers, particularly at low shear rate, with a pronounced effect in the case of basal fibers. A slightly higher shear thinning behavior of BF/PA66 with respect to GF/PA66 composites was confirmed by fitting the flow curves through the power law model. Finally, a worsening in fiber dispersion, by increasing the content in the matrix, and a weak compatibility between the two phases constituting the materials were highlighted through SEM micrographs.

Color Stability, Chemico-Physical and Optical Features of the Most Common PETG and PU Based Orthodontic Aligners for Clear Aligner Therapy

It is difficult to find research papers collecting comparative results about characterization studies of clear aligners. Therefore, the aim of this paper is to provide the first comparative analysis of most commercial clear aligners, in terms of their stability towards intra-oral staining agents, their physicochemical and optical properties, as well as their water absorption behavior. Five types of aligners, characterized by different techniques, are considered: Erkodur, Essix Plastic, Ghost Aligner, Zendura, and Invisalign. The obtained results show that clear aligners are made up of PETG, semi rigid PU, and a mixture of PU and PETG, with different degrees of crystallinity which affect the transparency of each aligner. In particular, the PETG-based materials reveal the highest value of short-range order and the highest properties in terms of transparency in the visible range. After 14 days of immersion into red wine and coffee, PETG and PU-based aligners reveal a perceivable change in color (NBS values from 1.5 to 3), corresponding to a loss of transparency due to the deposition of impurities on the surface. These results are particularly marked for Invisalign, showing changes towards other colors (NBS up to 35), probably due to the thermoforming process which led to the formation of a wrinkled surface entrapping the impurities.