Chaveewan Kongkaew

Preparation of Graft Copolymer of Natural Rubber and Polystyrene by Electron Beam Irradiation

The simultaneous graft copolymerization between natural rubber (NR) and styrene monomer (St) was induced by electron beam irradiation. The grafted polystyrene in graft copolymer was characterized by Fourier Transform Infrared Spectroscopy (FT-IR). This research investigated the influence of three factors (radiation dose, type of emulsifier and adding of sensitizer; normal butyl acrylate (n-BA)). It was found that the appropriated emulsifier was ammonium laurate which lead to higher monomer conversion and grafting efficiency. The adding of n-BA could notably enhance monomer conversion and crosslink density. Moreover increasing radiation dose, the monomer conversion and crosslink density increased. This technique was a cleaner and faster technology suitable for grafting application.

Comparison of Mechanical Properties of Three Different Orthodontic Latex Elastic Bands Leached with NaOH Solution

Orthodontic elastic bands made from natural rubber continue to be commonly used due to their favorable characteristics. However, there are concerns associated cytotoxicity due to harmful components released during conventional vulcanization (sulfur-based method). With the co-operation of The National Metal and Materials Technology Center (MTEC) and Faculty of Dentistry Mahidol University, a new method was introduced to reduce toxic components by leaching the orthodontic elastic bands with NaOH solution. The objective of this study was to evaluate the mechanical properties of Thai and commercial orthodontic elastic brands (Ormco and W&H) leached with NaOH solution. Three elastic brands (N =30, size 1⁄4 inch ,4.5 oz.) were tested for mechanical properties in terms of initial extension force, residual force, force loss, breaking strength and maximum displacement using a Universal Testing Machine. The results showed that force loss significantly decreased in Thai-LEACH and W&H-LEACH, whereas the values increased in Ormco-LEACH (P<0.05). The data exhibited a significantly decrease in breaking strength with Thai-LEACH and Ormco-LEACH, whereas all 3 brands revealed a significantly decrease in maximum displacement with the leaching process (P<0.05). In conclusion, leaching with NaOH solution is a new method, which can remove toxic components from orthodontic latex elastic bands. However, this process can affect their mechanical properties. Leached elastic bands from Thai had comparable properties with Ormco and have potential to be developed as a promising product.

Comparison of Mechanical Properties between Thai Orthodontic Elastics with Different Ammonia Contents and Commercial Orthodontic Elastics

Introduction: The most widely used preservative system for natural rubber latex to date is the ammonia-based system preventing spontaneous coagulation and putrefaction due mainly to bacteria contamination. Objectives: The study compared 2 types of Thai orthodontic elastics, produced from natural rubber latex with different ammonia contents with commercial orthodontic elastics in terms of initial extension force, residual force, force loss, swelling index, breaking strength and maximum displacement. Materials and Methods: Thai orthodontic elastics were developed from 2 types of natural rubber latex; low ammonia < 0.15% (Thai-L), and high ammonia not < 0.6% (Thai-H). The mechanical properties of Thai orthodontic elastics were compared with commercial elastics (Ormco). Mechanical properties were tested using a universal testing machine (Instron 5566). Data were analyzed by One-way ANOVA and Tukey’s test compared the measurements among groups. Results: Ormco had the highest initial extension force and showed significant differences with Thai-L and Thai-H. Thai-L had the highest residual force but showed no significant difference compared with Ormco. Thai-L had the lowest percent of force loss and showed significant differences with Thai-H and Ormco. Thai-L had lower force loss than Thai-H. For swelling index, Thai-L had the highest elasticity. For breaking strength and maximum displacement, both Thai elastics met the Australian Standard (AS) for breaking strength and maximum displacement, similar to Ormco elastics. Conclusion: All elastics met the specifications of the AS for breaking strength and maximum displacement. Thai-L had comparable properties with commercial orthodontic elastics in terms of mechanical properties. Thai-L had comparable properties with Ormco in terms of mechanical properties and may be developed for orthodontic purposes.