## 4 Conclusions  
This research highlights the benefits of PDCA methodology in quality improvement. It instructs the simplified way to practice this method with support tools such as the 5 Whys, Ishikawa diagrams, 5W2H, and Computer-Aided Design (CAD). Through the packaging case study, PDCA combined these tools and analyzed packaging defects, found root-causes, and facilitated development of more sustainable ways to tackle problems. The new packaging method not only uses environmentally friendly materials but also extremely reduces the defect ratio. With respect to the objectives of the case study, the new design uses 100% recyclable, biodegradable materials. It can minimize surface crack defects for mid-weight products or significantly reduce the defect ratio in large-weight products due to incidents in delivering and storing. The extra cost for the new packaging method is slightly higher than the old one, but the benefits of a higher competitiveness and customers' satisfaction can be exploited. For long-run evaluation, the new packaging design can help saving costs from decreasing the numbers of rejected defects or reworked products, reducing the packaging time and labor forces. These result for increasing customer satisfaction, the company's profit, quality as well as reputation. The PDCA cycle should be replicated for quality improvement, reducing defects and driving towards sustainability for packaging methods. Recommendations to successfully apply PDCA methodology are mentioned in the paper. In the Plan phase, keys for effective implementation are team establishment, teamwork spirit, using proper quality tools for gathering data, clearly defining problems, and the analysis of the current  
Figure 6: An example of a packaging standardization process.  
situation as well as of obstacles. The outcome of the Plan stage should include root-cause analysis, potential solutions, and a detailed implementation schedule with time-bounds. In the Do phase, implementing, refining, and finalizing countermeasures are essential actions. Using the right tools and techniques for these tasks will result in shortening the testing times and saving costs. In the Check stage, proper methods and plans for evaluations help to avoid erroneous data collection which can lead to wrong decisions in the Act phase. Finally, the Act phase should include tasks in documenting results, process standardization, sharing learnings, and planning of further steps.  
In conclusion, this research contributes understandable guidance with a successful benchmark application of PDCA for packaging problems. Through a packaging case study, it shows the art of combining scientific and practical methodology by utilizing tools in the PDCA cycle to achieve multipurpose objectives, i.e., responsibility in protecting the environment, increasing quality, and economic profit. Due to the limited number of studies about continuous improvements in the sustainable packaging field, the paper's application is expected to be highly useful for practitioners and researchers in similar quality projects. In addition, this simplified PDCA cycle with a combination of quality and design tools can effectively be applied in creating new designs, reducing defects as well as continuous quality improvement in any manufacturing field.  
Conceptualization, methodology, funding acquisition, supervision, V.N.; investigation, data curation, software, formal analysis V.N. and N.N.; project administration, visualization, writing--original draft preparation, T.T.; writing--review and editing, B.S. All authors have read and agreed to the published version of the manuscript.  
This research was funded by The Vietnam Ministry of Education and Training, grant number B2019-VGU-02  
The authors declare no conflict of interest.