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The aims of this experiment are to prepare urea-methanal from urea and methanol to compare the physical properties between the synthesised urea-methanal (thermosetting plastic) and polyethene (thermoplastic)

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Introduction

Date: 15/11/2011 Exp. No.: 26 Title: Synthesize urea-methanal and compare the properties between thermoplastic and thermosetting plastics Aim: The aims of this experiment are to prepare urea-methanal from urea and methanol to compare the physical properties between the synthesised urea-methanal (thermosetting plastic) and polyethene (thermoplastic) Introduction: Urea-methanal is a condensation polymer which contains amide cross linkages. Thus, it is a thermosetting polymer which shows a fire resistant property. In addition, it is very hard and widely used in making electrical sockets and plugs due to its insulating, low density but yet wear resistant properties. A simple synthesis of the polymer can be carried out by mixing equal amount of urea and methanal slowly in a container. In this experiment, urea-methanal is prepared and its properties are compared with a thermoplastic, polyethene in plastic wrap. Apparatus and chemicals: Apparatus: 100 cm3 measuring cylinder Boiling tube Dropper Tongs Hammer Bunsen burner Wooden stick Chemicals: 3 cm3 methanal 3 g of urea 20 cm3 of 1M Na2CO3 0.5 cm3 of concentrated H2SO4 A piece of plastic wrap Procedures: 1. About 3 g of urea was dissolved in 3 cm3 of methanal in a boiling tube. 2. About 0.5 cm3 conc. H2SO4 was added dropwise using a dropper with stirring and cooling in a water bath. 3. A piece of wooden stick was put into the solution mixture and the solution was allowed to polymerise. ...read more.

Middle

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 polymerization 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. ...read more.

Conclusion

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 1. Methanal was carcinogenic, so all steps involving methanal should be done in the fume cupboard. 2. After crushing the boiling tube, all the broken glass should be wrapped with newspaper and thrown away immediately. Reference: http://en.wikipedia.org/wiki/Urea-formaldehyde http://www.practicalchemistry.org/experiments/urea-methanal-polymerisation,260,EX.html http://www.ehow.com/about_5045730_properties-polyethylene.html http://www.sandwichpanels.org/articles/article_thermoplasticresin.html http://www.engineeringtoolbox.com/physical-properties-thermoplastics-d_808.html http://www.ami.ac.uk/courses/topics/0210_pt/solutions/sol_01.html http://wiki.answers.com/Q/What_are_thermoset_plastics http://www.grecycling.com/company.asp http://www.recycledplastic.com/resource/plastic/thermoplastics-vs-thermosettin-plastics/ http://www.thomasnet.com/about/thermoset-plastics-61020277.html http://en.wikipedia.org/wiki/Thermoplastic ?? ?? ?? ?? ...read more.

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