# Optimisation of Shrinkage and Strength on Thick Plate Part Using Recycled LDPE Materials
## 4 Conclusions  
Using a combination of virgin and recycled materials has a great impact on the quality of thick plate parts moulded through the injection moulding process. The shrinkage and strength were optimised by using the RSM and PSO methods. Several conclusions can be drawn from this study:  
* Based on the ANOVA analysis conducted in FFD, the most significant parameter influencing the shrinkage in the \(x\) direction is the packing pressure for all virgin to recycled ratio materials. Meanwhile, recycled materials of R30, R40 and R50 showed that the mould temperature is the most significant parameter influencing the \(y\) direction of shrinkage. Lastly, packing pressure was found to be the most significant processing parameter affecting the strength of R0 and R30, while mould temperature is the most significant processing parameter affecting the strength of R40 and R50.
* The shrinkage in the \(x\) and \(y\) directions continues to increase when the amount of recycled ratio increases as compared to fully virgin material, while the tensile strength of the thick plate part continues to decrease when the amount of recycled ratio increases.
* After applying the RSM and PSO methods, the specimen with 30% recycled material (R30) showed the closest shrinkage and tensile strength quality performance to the R0 specimen.
* The validation test results indicated that the optimal setting of processing parameters, as suggested by PSO and RSM optimisation methods, is acceptable, since the errors were all below 10% as compared to the real measured data.  
Conceptualization, N.R., S.Z.A.R., M.N.M.S. and M.F.G.; methodology, J.S., D.K., S.Z.A.R. and M.N.M.S.; software, N.R., A.E.-h.A., P.P. and J.O.C.V.; validation, K.B., P.P., M.N., J.S. and D.K.; formal analysis, N.R., A.E.-h.A. and M.N.M.S.; investigation, S.Z.A.R., J.O.C.V. and M.N.M.S.; data curation, N.R. and S.Z.A.R.; writing--review and editing, K.B., N.R., S.Z.A.R., M.M.A.B.A., J.O.C.V., J.S., M.N. and M.F.G.; project administration, S.Z.A.R., M.M.A.B.A. and A.E.-h.A. All authors have read and agreed to the published version of the manuscript.  
The authors wish to thank the Ministry of Education, Malaysia, for their financial support of this study through Fundamental Research Grant Scheme (FRGS), FRGS/1/2019/TK03/UNIMAP/02/20.  
Data Availability Statement: Data sharing not applicable.  
The authors declare no conflict of interest.  
\begin{table}
\begin{tabular}{c c c c c c c c} \hline \multirow{2}{*}{**Parameter/Response**} & \multicolumn{2}{c}{**R0**} & \multicolumn{2}{c}{**R30**} & \multicolumn{2}{c}{**R40**} & \multicolumn{2}{c}{**R50**} \\ \cline{2-9}  & **RSM** & **PSO** & **RSM** & **PSO** & **RSM** & **PSO** & **RSM** & **PSO** \\ \hline \multirow{2}{*}{\begin{tabular}{c} Mould temperature (\({}^{\circ}\)C) \\ Melt temperature (\({}^{\circ}\)C) \\ Packing pressure (MPa) \\ Cooling time (s) \\ \end{tabular} } & 49.95 & 52.46 & 57.36 & 59.92 & 51.67 & 49.95 & 59.56 & 59.56 \\  & 179.96 & 179.80 & 167.43 & 165.05 & 177.31 & 179.88 & 167.79 & 167.79 \\  & 12.46 & 18.52 & 18.50 & 18.51 & 14.39 & 12.78 & 16.18 & 16.18 \\  & 24.08 & 22.01 & 23.84 & 25.34 & 19.49 & 19.43 & 23.96 & 23.96 \\ \hline \multirow{2}{*}{\
\begin{tabular}{c} Tensile strength \\ (by optimisation method) (MPa) \\ Tensile strength \\ (validation test) (Mpa) \\ \end{tabular} } & 9.86 & 9.97 & 9.81 & 9.71 & 9.66 & 9.71 & 9.57 & 9.62 \\  & 9.73 & 9.77 & 9.69 & 9.58 & 9.64 & 9.54 & 9.45 & 9.56 \\ \hline \multirow{2}{*}{
\begin{tabular}{c} Error (\%) \\ \end{tabular} } & 1.34 & 2.05 & 1.24 & 1.36 & 0.21 & 1.75 & 1.27 & 0.62 \\ \hline \end{tabular}
\end{table}
Table 11: Validation test for tensile strength of part.