CP5065-2021S1-2A04-Group1: Week 4

Week 4 {6.5.2021}

Material Selection

Hi all, this week the lesson was conducted asynchronously and we were supposed to select materials for a given product, taking into consideration its functional and ecological requirements.

In our material selection, we made use of the COWS decision matrix. A method we learned in our Year 1 module, Materials for design.

COWS decision matrix

C – Criteria. Develop a hierarchy of criteria, also known as the decision model.

O – Identify the options, also known as solutions or alternatives.

W – Assign a weightage to each criterion based on its importance in the final decision.

S – Rate each option on a ratio scale by assigning it a score of 1 to 3 based on each criterion. The final score is calculated as Rating x Weight for each material

Assignment for this week

The group had been tasked to select a material for a single-use disposable water bottle that would cause minimal harm to the environment. The current material of a disposable water bottle is plastic, which causes various negative effects on the environment such as the long period of time to decompose (About 20 - 500 years). It also contributes to global warming, threatens wildlife, and spreads toxins. Hence, we want to choose a material that is more environmentally friendly and has a faster decomposition time.

To help us decide which material is best to use, we shortlisted a few materials that we would later research and evaluate more on, with the aid of the COWS decision matrix.

We ultimately chose to evaluate these 4 materials, namely Polylactic Acid, Polyethylene terephthalate, Polyethylene Furanoate (Plant), polyhydroxy butyrate. This is because these 4 materials are biodegradable and hence relatively environmentally friendly.

We decided to evaluate them based on the following criteria:

Low density🍃
High melting point 🧊
High Yield Strength🏋🏻
Biodegradability♻️
and Waterproof💧

Firstly, we collected the data for density, melting point, yield strength, and biodegradability of the four materials and evaluate whether they are waterproof or not.

Secondly, we divided the weightages for each criterion according to their importance for the disposable bottle and we performed the COWS Decision Matrix to see which material has the highest score. Polyhydroxy butyrate ended up with the highest score among the four materials, so it might be an ideal material for the disposable bottle.

Thirdly, we proceeded to choose the most economical material among the three materials with the best score according to our COWS Decision Matrix.

We are evaluating toxicity under the economical aspect as a toxic material will result in a huge expense for clean-up, disposal, and even during the handling in manufacturing.

We conducted another COWS Decision Matrix and we concluded that polylactic acid is the most suitable material for a single-use water bottle that does minimal harm to the environment. It scored a total of 485 points when compared to 3 other materials. Polyhydroxy butyrate came in close at 480 points but its high cost of material proved too costly for companies to take it up as a viable material for manufacturing water bottles.

Polylactic proves to be a suitable material, indicating consistent desirable results. In the evaluation of its properties, it scored higher or on par with its close competitor polyhydroxy butyrate in almost every category except for its biodegradability characteristics which prove to poorer by about 4 days, which is a relatively insignificant amount of time as compared to the many years it takes for Polyethylene terephthalate and Polyethylene Furonoate (Plant) to biodegrade.

References

CP5065-2021S1-2A04-Group1

Pages

Week 4

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