# Amplification Ratio of a Recycled Plastics-Compliant Mechanism Flexure Hinge
## 4 Conclusions  
This study focuses on making plastic flexure hinges out of various plastics such as ABS, PP, HDPE, and LDPE/TPU blend. The recycle ratios are also examined to improve the hinge efficiency. The amplification ratios of different recycle ratios and plastic types were measured and compared. Some interesting results that could be named are:  
1. The input and output displacements of all PP, ABS, and HDPE hinges are in a linear relationship. The existence of recycled plastics has no effect on this principle. The pure PP, ABS, and HDPE flexure hinges achieve the highest amplification ratios of 5.728, 8.249, and 5.668. The amplification ratio is lowered by the addition of recycled plastics. However, this amplification ratio reduction is not very high. In comparison to pure plastic hinges, the 25% recycling ratio PP, ABS, and HDPE flexure hinges obtain an amplification ratio that is 12%, 13.3, and 21.7% lower. Furthermore, the use of recycled plastics could reduce the requirement for new plastic created from raw resources.
2. With the PP flexure hinge, a maximum input value of 157 \(\upmu\)m could lead to an output value of 886 \(\upmu\)m. However, the ABS flexure hinge could gain an output value of  
Figure 8: SEM microstructure of the plastic flexure hinges: (**a**) ABS, (**b**) PP, (**c**) HDPE, and (**d**) LDPE/TPU.  
833 \(\upmu\)m at a maximum input value of 115 \(\upmu\)m. Finally, with the HDPE flexure hinge, a maximum input value of 175 \(\upmu\)m could lead to an output value of 857 \(\upmu\)m. For the PP, ABS, and HDPE flexure hinges, respectively, the average amplification ratio values of all recycling ratios are 5.35, 7.60, and 5.02. In terms of amplification ratios, the ABS flexure hinge is often better than the PP and HDPE flexure hinge. The HDPE flexure hinges have the lowest amplification ratio among these plastic types.
3. The amplification ratio typically develops as more TPU is added to the LDPE/TPU blend. The TPU's strong compatibility with the LDPE polymer may be the reason for this. The LDPE/TPU blend hinge offers a broader range of amplification ratio of 2.85-10.504 than the PP, ABS, and HDPE flexure hinges. It is noteworthy that altering the blend percentage has a much greater impact on the amplification ratio than adjusting the recycling ratio. By identifying the best plastic kinds, the findings expand the range of uses for plastic flexure hinges. Besides finding suitable plastics, further investigations could survey the effects of the hinge shape, the hinge dimension, and the hinge design on its performance. The temperature condition, humidity, and degradation could also impact the plastic flexural hinge and need further investigation.  
P.S.M. and V.-T.N.: conceptualization, funding acquisition; V.-T.N.: writing original draft, investigation; T.M.T.U., T.T.D., P.S.M., H.N.L.D. and V.-T.N.: analyzing, visualization, project administration; V.T.T.N., H.N.L.D., P.S.M. and V.-T.N.: writing--review and editing. All authors have read and agreed to the published version of the manuscript.  
The authors acknowledge the support of HCMC University of Technology and Education for this study.  
Not applicable.  
Data Availability Statement: Data is contained within the article.  
The authors declare no conflict of interest.