5. If the polymer was not stuck to the wooden stick, a hammer was used to break to boiling tube wrapped with newspaper.
6. The polymer was carefully taken out using a pair of tongs.
7. The polymer product was compared with plastic wrap in the following catagories.
- Flammability
- Hardness
- Transparency
- Melting behavior
8. To compare the flammability and melting behavior, the 2 plastic were burnt with a Bunsen flame.
9. To compare their hardness and transparency, direct observation were taken.
Observations:
- Urea was in white crystal form.
- Methanal had a pungent smell.
- When sodium carbonate was added into the boiling tube, there were colourless gas bubbles evolving out.
For the polymer product (Urea methanal)
- The polymer product was white solid (not transparent).
- It was not flammable and upon heating with Bunsen Burner, but instead, it turned black.
- It did not melt upon heating.
- It was very hard.
For plastic wrap
- It was transparent.
- It was flammable upon heating with Bunsen burner.
- It also started to melt when heated.
- It was soft but tentile but of a high tensile strength.
Discussion:
Urea methanal
Urea methanal has a formaula of .
The raw materials of producing urea methanal are urea and methanal.
This is a condensation polymerization with the elimination of a water molecule.
It is very hard because there are hydrogen bonds attractions betweens layers and methanal also acted as a reagent which can produce cross linkage between layers.
Therefore, layers are bonded with strong covalent bondings which enhance its physical hardness.
The structure is as follow:
Urea methanal has a high , flexural modulus, heat distortion temperature, low water absorption, mould shrinkage, high surface hardness, elongation at break, and volume resistance.
With these properties, it is a very good material for making sockets and many other electrical appliances casing as it does not catch on fire in high temperature and has a very high tensile strength.
So, it is safe to use this kind of plastic for sockets are it does not burn in flame when short circuit occurs.
Socket made using urea methanal
Polythene
Plastic wrap is made of polythene and the raw material of polythene is ethene.
The structure of polythene is
Plastic wrap
This polymerization is an addition polymerization.
It is a tough, white, translucent, waxy thermoplastic. It is used for packaging, bottles, toys, wood preservation, electric cable, pipes, and tubing.
Polythene is produced in two forms: low-density polythene, made by high-pressure of ethene gas, and high-density polythene, which is made at lower pressure by using catalysts.
Thermoplastic and thermoset plastic
Plastics are divided into two groups depending on how it reacts to heat. Thermoplastics can be repeatedly softened by heating and hardened by cooling. Thermosetting plastics, however, harden permanently after being heated once.
Thermoplastics are plastic that can be heated to molten form and cooled down to solid unlimited number of times. Polythene and PVC are examples of this kind of plastic. This kind of plastic is very useful as it can be melted and molded to a desired shape.
Thermoplastics have a wide range of properties. They can be soft and ductile, like rubber, or hard and durable, like metal. Some thermoplastics are heat-resistant at 600 degrees Fahrenheit, while others are cold-resistant at -100 degrees Fahrenheit.
Depending on what elements are used in their processing, thermoplastics can be used as insulators to protect against heat and electricity, or can even conduct electricity.
These plastic balls are made of thermoplastic
Advantages
Thermoplastics can be molded into any shape, are generally lightweight and cost little to make. They can replace metals when weight is an issue and can be crafted with a high degree of precision. They can also withstand more stress than metal without deforming, meaning metal would bend before plastic would. Thermoplastics are used in computer, medical, automobile and many other manufacturing industries.
Disadvantages
The biggest disadvantage to thermoplastics is that they can melt when they're heated. They can also suffer damage from sunlight. And unlike metals, they're susceptible to deformation after long-term stress. Thermoplastics also tend to break rather than deform under excessive stress.
Manufacturing
Thermoplastics are manufactured principally by injection molding, thermoforming, and extrusion molding. With injection molding, melted plastic is forced into a cold mold under high pressure. Thermoforming heats plastic films to soften them, then pushes them into a mold by a vacuum or plug. Extrusion molding forces the melted plastic through a die, which creates the shape of the plastic. Pipe, film, and electrical wire insulation are examples of plastic products molded by extrusion.
A picture of injection molding in industry
This kind of molding is usually used to make plastic in shape of pipes.
This kind of molding is used to make plastic into the shape of containers such as bowls
Recycling
Thermoplastics are recyclable resin compounds that can be reused and reformed after reprocessing. The recycling of thermoplastic can reduce trash, cut processing costs, and can help save the environment. After reprocessing, the recycled plastic is reground into pellets which are melted and used for injection or extrusion molding.
Plastic is reprocessed into pellets and are ready to be reused
A thermosetting plastic is a nonmeltable plastic that was made by melting down a powder and when that happens, all the little plastic molecules theoretically combine to make one giant molecule. This is why you can’t remelt it, all that would happen if you tried to melt the thermoset plastic, is the plastic would burn away.
Urea methanal is an example of this kind of plastic.
Thermosetting plastic cannot be melted once it hardens. This kind of plastic is useful when the plastic should not be melt even under high temperature such as sockets.
This character of this platic is given by the cross linkage between polymer chains.
Thermosetting plastic form permanent chemical bonds or cross links with each other once heated. Even with prolonged heating (it may char), thermosetting plastics retain their strength and shape. This makes thermosetting plastics ideal for producing heat resistant products such as insulation parts, car parts, etc…
Recycling
Unlike thermoplastic, thermosetting plastic cannot be melted and remolded. So, it would be much more difficult to recycle these kinds of plastic.
Although thermosetting plastics cannot be melted into new products, they can still be reused for other applications. An excellent example is polyurethane foam. Flexible polyurethane foams are commonly shredded into small flakes and re-manufactured into carpet underpayment.
Precautions of the experiment
- Methanal was carcinogenic, so all steps involving methanal should be done in the fume cupboard.
- After crushing the boiling tube, all the broken glass should be wrapped with newspaper and thrown away immediately.
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