# Optimisation of Shrinkage and Strength on Thick Plate Part Using Recycled LDPE Materials
## 3 Results and Discussion
### Validation Test Results  
Tables 9-11 present the results of the validation test for shrinkage in the \(x\) and \(y\) directions and tensile strength of the specimens by applying the optimal settings of processing parameters as suggested from the RSM and PSO analysis for R0, R30, R40 and R50 specimens. The validation data is quite revealing in such a way that the percentage differences between the results achieved from the validation test in comparison with the optimisation method has minimal error of between 0.21% to 8.07%, indicating that optimal settings of processing parameters produced by optimisation methods were acceptable to mould parts made of recycled LDPE, since the percentage errors are all below 10% [17; 48].  
\begin{table}
\begin{tabular}{c 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{3}{*}{Mould temperature (\({}^{\circ}\)C)} & 40.35 & 40.09 & 48.03 & 48.70 & 49.36 & 48.77 & 46.92 & 47.00 \\  & Mult temperature (\({}^{\circ}\)C) & 179.77 & 179.91 & 178.92 & 179.88 & 180.00 & 179.62 & 177.15 & 179.96 \\ \cline{1-1}  & Packing pressure (MPa) & 18.48 & 18.41 & 12.82 & 18.54 & 12.72 & 12.28 & 13.96 & 12.33 \\ \cline{1-1}  & Cooling time (s) & 22.65 & 22.67 & 24.43 & 24.26 & 25.23 & 26.50 & 25.27 & 26.48 \\ \hline \multirow{3}{*}{Shrinkage (by optimisation method) (\%)} & 1.92 & 1.92 & 2.01 & 1.87 & 2.05 & 2.01 & 2.08 & 1.97 \\ \cline{1-1}  & Shrinkage (validation test) (\%) & 2.08 & 2.01 & 2.08 & 2.05 & 2.16 & 2.11 & 2.19 & 2.10 \\ \hline \multicolumn{1}{c}{Error (\%)} & 7.69 & 4.48 & 3.37 & 8.78 & 5.09 & 4.74 & 5.02 & 6.19 \\ \hline \end{tabular} Remarks: R0: 100:0 recycled ratio blend; R30: 70:30 recycled ratio blend; R40: 60:40 recycled ratio blend; R50: 50:50 recycled blend.  
\end{table}
Table 10: Validation test for shrinkage in the \(y\) direction.  
\begin{table}
\begin{tabular}{c 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{3}{*}{Mould temperature (\({}^{\circ}\)C)} & 59.20 & 60.00 & 42.41 & 40.48 & 41.42 & 41.46 & 46.53 & 40.09 \\  & 175.41 & 174.16 & 160.00 & 160.25 & 160.00 & 160.35 & 170.42 & 170.58 \\ \cline{1-1}  & Packing pressure (MPa) & 15.85 & 16.08 & 18.56 & 18.25 & 18.51 & 18.55 & 16.49 & 17.88 \\ \cline{1-1}  & Cooling time (s) & 22.21 & 23.62 & 19.42 & 19.72 & 19.42 & 19.66 & 19.48 & 19.48 \\ \hline \multirow{3}{*}{Shrinkage, \% (by optimisation method) (\%)} & \multirow{3}{*}{1.85} & \multirow{3}{*}{1.71} & \multirow{3}{*}{2.45} & \multirow{3}{*}{2.56} & \multirow{3}{*}{2.65} & \multirow{3}{*}{2.75} & \multirow{3}{*}{2.80} & \multirow{3}{*}{2.75} \\  & & & & & & & & \\ \cline{1-1}  & Shrinkage, \% (validation test) & 1.95 & 1.86 & 2.49 & 2.68 & 2.67 & 2.79 & 3.02 & 2.90 \\ \hline \multicolumn{1}{c}{Error (\%)} & 5.13 & 8.07 & 1.61 & 4.48 & 0.75 & 1.43 & 7.28 & 5.17 \\ \hline \end{tabular} Remarks: R0: 100:0 recycled ratio blend; R30: 70:30 recycled ratio blend; R40: 60:40 recycled ratio blend; R50: 50:50 recycled blend.  
\end{table}
Table 9: Validation test for shrinkage in the \(x\) direction.