Week 4

Materials for design recap

This week, we had to recap of Year One module, Materials for Design (MFD) to complete our assignment. 

MFD is very relevant to Chemical product design as designing an engineering product involves 3 interrelated problems:

1. Selecting a material 👕

2. Specifying a shape ⃝

3. Choosing a manufacturing process 🔨

COWS: 📊

The COWS method is described as follows:

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 weight to each criterion based on its importance in the final decision. 

S – Rate each option on a ratio scale by assigning it a score or rating against each criterion. The score is       calculated as Rating x Weight.

The scores are then evaluated, and solutions with the highest scores are the ones that best meet the criteria.

Assignment for Group 4:

Our assignment was to select materials for the teat and cover of a polycarbonate baby milk bottle 🍼.

We have decided to use (material to chosen) as the teat and the (material to chosen) as the cover.

As for the final material to be chosen, we will use the COWS decision matrix to help us decide.

Product: Milk bottle 

Milk bottle can be divided into 3 parts: 

1. Teat 

2. Body of bottle 

3. Cover of bottle 

For this assignment, we will focus on selecting the material for the teat and cover of the bottle. 

Table 1: Teat 

Function	Transfer liquid to an infant
Constraints	Chemical compatibility to milk High Tensile Strength High Flexibility Biocompatible Light weight
Objectives	Maximize flexibility

Based on the constraints and objectives, we will rank the requirements and assign a weightage based on their importance. 

Reasons for constraints: 

• To be flexible, the teat must be soft enough so that it does not damage the user’s mouth. It also must not pose a choking hazard to the user. Hence, it must be elastic. 

• The teat must be strong enough to not break easily when the user bites on it or dropped to the ground. Therefore, it must have high tensile strength. 

• For the teat to be long-lasting, the teat must be able to withstand exposure to different substances, such as the user’s saliva and milk. Thus, it must be corrosion resistant. 

• The teat should not be able to cause damage to the user’s body through chemical means, like causing a toxic reaction to the user’s nervous system. Hence, it must be biocompatible. 

• The user should be able to hold the bottle with ease. Therefore, the teat must be lightweight. 

 

Based on table 1, the materials that have been shortlisted are silicone, latex, rubber. 

Table 2: Properties of the Teat 

	Materials
Criteria	Silicone	Latex	Rubber
Compatibility with Milk	A- Excellent	A – Excellent	A – Excellent
Ultimate Tensile Strength (MPa)	3.95	17.5	17.5
Young’s Modulus (elasticity) (GPa)	0.0255	0.1	0.002
Biocompatibility	Yes	Yes	Yes
Density (g/cm3)	1.7	0.977	1.05

 

Then, to compare and rate, the COWS decision matrix is applied. Based on the result, silicone is the highest candidate with latex being second by just slightly behind while rubber is at the last. 

Another COWS table is done to further identify which material is most suited, this time economic criteria are considered. 

Based on this selected material is Latex. 

Therefore, since latex is only slightly behind in the first COWS matrix and scored the highest in the COWS matrix for the economic material, latex is the selected material for the bottle's teat. 

Next, we choose a material for the cover.

 

Based on the constraints and objectives, we will rank the requirements and assign a weightage based on their importance. 

Reasons for constraints: 

• The cover must be strong enough such that it does not break easily, for example, when it is dropped to the ground. Hence, it must have high ultimate tensile strength. 

• The cover must be non-toxic so that it does not harm the user if they come into contact with it. 

• The cover must be chemically resistant so that it does not corrode if it is exposed to different substances, such as the user’s saliva and milk. 

• The user should be able to hold the bottle with ease. Therefore, the cover must be lightweight. 

• The cover must have a high melting point so that it does not melt when heat is transferred from the warm milk to itself. 

• 
  

Based on table 5, the materials that have been shortlisted are polyethersulfone, polycarbonate, glass.  

Next, we research the properties of each material.

Then, to compare and rate, the COWS decision matrix is applied. Based on the results, polyethersulfone is the highest candidate with glass being second by just slightly behind while polycarbonate is at the last. 

Another COWS table is done to further identify which material is most suited, this time economic criteria are considered. 

Based on this, Polyethersulfone is selected. 

Therefore, since polyethersulfone is rated the highest for both COWS matrix tables, polyethersulfone is the selected material for the cover of the bottle. 

Reflection 📜:

~Trisyia 🐌~

This week we had no class. We were given slides to guide us on the assignment given. It was manageable as we had actually done this before in a module we learned previously in year 1 called materials for design. We referred to our old notes and the notes given for this lesson to complete the assignment. 

~Jun Ying🚲~

In this asynchronous lesson, we had to recall and apply what we have learned in Materials for Design(MFD) in Year 1 to do the assignment. Honestly, this was perfect timing for me as I had not been revising my Year 1 materials, and had forgotten much of what I had learnt, so the revision videos on Blackboard were a crucial refresher for me. My groupmates and I had no issues doing the assignment, except when I was doing research for some properties of materials, which took quite a long time to find, making me feel dismayed. In particular, finding the density of latex was quite difficult, as there was not much information about it. After noticing that I was irritated after researching for so long, I decided to take a short break by grabbing a snack. After that, I was able to find its density after a short while, making me feel satisfied. After this week, I will revise my Year 1 materials from time to time so that I will not make the mistake of forgetting the content again.

~John👽~

For this week, it was an asynchronous lesson therefore we did not have any classes for this week. It also was a holiday during that day therefore it was rather convenient for us as we did it at home. Here we recapped what we had learned during our year 1 which is the COWS decision matrix to choose the material for a baby bottle. Personally I had forgotten a lot about the COWS decision matrix thus I had to look for my year 1 notes in order for me to recall what I have learnt. After reading up on the notes, I had a better understanding again and proceeded to do the activity that was given to us. A lot of research was done but we had a lot of time and thankfully in the end we managed to find all the information needed. This week was a good way for me to recall all the things that I have learnt in the module Material For Design and I hope I can continue to make use of this information.