Enhancing the Mechanical Properties and Aging Resistance of 3D-Printed Polyurethane through Polydopamine and Graphene Coating

Preparation of quaternary ammonium lignosulfonate modified UV resistant polyurethane and its application in leather dyeing

Applying cationic waterborne polyurethane (CWPU) in the leather color-fixing process can improve the dyeing rate and enhance color fastness. However, under prolonged exposure to sunlight, CWPU will age and degrade and the leather will fade in color, become stiff and crack easily. In this study, an Ultraviolet absorber was introduced into cationic waterborne polyurethane (UVCWPU) and quaternary ammonium Lignosulfonate (QLS) was prepared by quaternization. Quaternary ammonium Lignosulfonate/UV-resistant waterborne polyurethane (QLS/UVCWPU) composite was prepared by the blending method. A one-way experiment was carried out to investigate the effect of the additional amount of quaternary ammonium reagent on the degree of modification of QLS, and the results showed that when the ratio of 3-chloro-2-hydroxypropyltrimethylammonium chloride (CHPTMAC) to LS was 7:1, the isoelectric point of the prepared QLS reached 6.65, and the content of N was 4.32 % so that the quaternary ammonium lignosulfonate modification was successful. QLS/UVCWPU was used to solidify the leather at pH 4.0 and a dosage of 4 %. The dye absorption rate of the leather increased to 97.3 %, the K/S value of the dyed gray leather reached 28.51, the color fastness to dry rubbing was improved to grade 5, and the color fastness to wet rubbing was up to grade 3 and enhancing the color fastness to sunlight, slowing down the effect of ultraviolet aging, and improving the antimicrobial properties of the leather.

Influence of Post-Processing on the Degree of Conversion and Mechanical Properties of 3D-Printed Polyurethane Aligners

BACKGROUND

This study explores how different post-processing methods affect the mechanical properties and degree of conversion of 3d-printed polyurethane aligners made from Tera Harz TC-85 resin.

METHODS

Using Fourier-transform infrared (FTIR) spectroscopy, the degree of conversion of liquid resin and post-processed materials was analyzed. This investigation focused on the effects of various post-curing environments (nitrogen vs. air) and rinsing protocols (centrifuge, ethanol, isopropanol, and isopropanol + water). The assessed mechanical properties were flexural modulus and hardness.

RESULTS

The degree of conversion showed no significant variance across different groups, though the polymerization environment influenced the results, accounting for 24.0% of the variance. The flexural modulus varied considerably, depending on both the rinsing protocol and the polymerization environment. The standard protocol (centrifugation followed by nitrogen polymerization) exhibited the highest flexural modulus of 1881.22 MPa. Hardness testing revealed significant differences, with isopropanol treatments showing increased resistance to wear in comparison to the centrifuge and ethanol rinse treatments.

CONCLUSIONS

This study conclusively demonstrates the adverse effects of oxygen on the polymerization process, underscoring the critical need for an oxygen-free environment to optimize material properties. Notably, the ethanol rinse followed by nitrogen polymerization protocol emerged as a viable alternative to the conventional centrifuge plus nitrogen method.