## 5 Result and Discussion  
Table 6 shows the results of impact weight (\(w_{\text{p}}\)) about five types of DMUs. The value of \(w_{\text{p}}\) indicates the contribution level of \(E_{\text{p}}\) for PSI. In Table 6, the contribution level of \(E_{\text{p}}\) for PSI will increase with the \(w_{\text{p}}\) increase. Table 7 shows the results of packaging sustainability indicator and environmental efficiency of five packaging systems in the three-stage Network DEA model. The packaging sustainability indicator of PrePack (DMU1) is the largest, up to 1, while the Tetra Pak (DMUs) come second after PrePack (DMU1), whereas the Composite box (DMU3) is found to have the lowest PSI, just 0.66. When compared with LCA method, the evaluation results of the three-stage Network DEA model and the ranking are consistent [28; 29]. \begin{table}
\begin{tabular}{c c c c} \hline \hline
**Stage** & \(\mathbf{w_{1}}\) & \(\mathbf{w_{2}}\) & \(\mathbf{w_{3}}\) \\ \hline PrePack (DMU1) & 0.2224 & 0.2985 & 0.4791 \\ Interpolation (DMU2) & 0.3429 & 0.3285 & 0.3286 \\ Composite box (DMU3) & 0.2823 & 0.3588 & 0.3589 \\ Interpolation (DMU4) & 0.3220 & 0.4162 & 0.2618 \\ Tetra Pak (DMUs) & 0.0001 & 0.1233 & 0.8766 \\ \hline \hline \end{tabular}
\end{table} 
Table 6: The results of impact weight (\(w_{\text{p}}\)) about five types of DMUs. \begin{table}
\begin{tabular}{c} cubic-Hermite \\ interpolation \\ \end{tabular} & [29; 30] \\ \hline \hline \end{tabular}  
* Data from CLCD-China-ECER 0.8 database. *
* \(y_{\text{3}_{j}}\) = the production of packaging materials
* the recycle rate. The recycle rate of PrePack, Composite box and Tetra Pak are 35%, 20% and 47%, respectively.  
\end{table} 
Table 5: The original data of five types of DMUs in the three-stage Network DEA model. \begin{table}
\begin{tabular}{c c c c} \hline \hline
**Stage** & \(\mathbf{psi}\) & \(\mathbf{Ev}\) & \(\mathbf{Ev}\) \\ \hline PrePack (DMU1) & 0.2224 & 0.2985 & 0.4791 \\ Interpolation (DMU2) & 0.3429 & 0.3285 & 0.3286 \\ Composite box (DMU3) & 0.2823 & 0.3588 & 0.3589 \\ Interpolation (DMU4) & 0.3220 & 0.4162 & 0.2618 \\ Tetra Pak (DMUs) & 0.0001 & 0.1233 & 0.8766 \\ \hline \hline \end{tabular}
\end{table} 
Table 6: The results of impact weight (\(w_{\text{p}}\)) about five types of DMUs. For plastic packaging, the fossil fuels category presents the largest contribution by the raw material from crude oil. Approximately 99% of the plastics produced today are petroleum-based, and the packaging industry alone consumes over 38% of these plastics [33]. However, PrePack has less demand for resources and energy. The production technology of PrePack is simple by three-layer low-density polyethylene coextrusion. Therefore, PrePack is the more sustainable one compared to other packaging systems. As we all know, there needs a fixed cost for a series of packaging production equipment to normal work. For Tetra Pak, the application widely and large batch production made lower resource consumption of unit package relative to other packaging systems. For the Composite box (DMU\({}_{3}\)), it is usually on a small scale, resulting in a higher resource consumption per unit package relative to other packaging systems. Tetra Pak and composite box are multi-layer (PE/cardboard-PE-Al-PE/PE and PA/cardboard/PE) composite materials and complexity production technology, but the recycle rate of Tetra Pak is up to 47%, causing the environmental burden to be reduced in packaging wastes treatment. In terms of environmental efficiency, \(E_{3}\) of the Composite box (DMU\({}_{3}\)) equals 0.0816 in the stage of packaging wastes treatment. \(E_{2}\) of Tetra Pak (DMU\({}_{3}\)) equals 0.4097 in packaging system manufacturing, less than 1(inefficient). We can base on interpolation DMU\({}_{4}\) to improve the inefficient DMU\({}_{3}\) by adding the recycling rate of DMU\({}_{3}\) and reducing CO\({}_{2}\) emission, while based on interpolation DMU\({}_{4}\) to improve the Tetra Pak (DMU\({}_{3}\)), by reducing the weight of single layer and the number of layers.