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. 2025 Jan 8;17(2):143.
doi: 10.3390/polym17020143.

Effect of Repeated Autoclave on Hardness and Tensile Strength of Polypropylene/Natural Rubber Developed for Rubber Dam Clamp

Thitaporn Nonthiphalang  1 , Panupat Phumpatrakom  2 , Paphavarin Rangsantham  2 , Panjaporn Wongwitthayakool  3 , Chakrit Sirisinha  4 , Nantawan Krajangta  1
Affiliations

Effect of Repeated Autoclave on Hardness and Tensile Strength of Polypropylene/Natural Rubber Developed for Rubber Dam Clamp

Thitaporn Nonthiphalang et al. Polymers (Basel). .

Abstract

In this study, we aimed to explore the feasibility of utilizing polypropylene (PP) and natural rubber (NR) blends as alternative materials for rubber dam clamps in dentistry. The hardness of various PP/NR blend ratios was compared to the commercial product SoftClampTM. Selected blend ratios exhibiting hardness values resembling rigid plastic were further evaluated for hardness and tensile strength after undergoing 1, 5, and 10 autoclave cycles. One-way ANOVA test results found that the PP/NR blends exhibited significantly lower hardness (p < 0.001) than the commercial SoftClampTM. PP/NR ratios of 100/0, 90/10, and 80/20 exhibited hardness levels equivalent to 82%, 80%, and 75% of SoftClampTM, respectively. Two-way ANOVA revealed significant reductions in hardness (p < 0.001) and tensile strength (p < 0.001) with increasing NR content across all autoclave cycles. However, post-autoclave assessments at 1, 5, and 10 cycles demonstrated no statistically significant differences in tensile strength (p = 0.058) and hardness (p = 0.52) for PP/NR ratios of 100/0, 90/10, and 80/20 compared to their pre-autoclave states. The NR content within the PP/NR blends decreased hardness and tensile strength, while autoclaving did not significantly affect the hardness and tensile strength of the PP/NR blends.

Keywords: hardness; natural rubber; polypropylene; rubber dam clamp; sterilization; tensile strength.

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Conflict of interest statement

The authors declare no conflicts of interest.

Figures

Figure 1
Figure 1
Experimental design.
Figure 2
Figure 2
Tensile strength specimen. (a) Specimen dimensions; (b) the different blend ratios of the specimens.
Figure 3
Figure 3
SEM images of the cross-sectional surface of tensile specimens before and after 10 autoclave cycles. SEM image at ×500 magnification of pre-autoclave specimens (a–c) and specimens after 10 autoclave cycles (d–f). SEM image at ×2000 magnification pre-autoclave specimens (g–i) and specimens after 10 autoclave cycles (j–l). Subfigures represent PP/NR blend ratios (100:0, 90:10, and 80:20).
Figure 4
Figure 4
The reaction scheme of thermo-oxidative degradation of the NR phase during blending at a high temperature of 175 °C.
See this image and copyright information in PMC

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