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Lab workshop
Characterisation, Testings and Identification of Various Plastics
Background
A plastic is a macromolecular substance and it is made from the linking up of the monomer through covalent bonds. A co-polymer is formed if more than one monomer is involved in the linking-up process. Plastics can be classified as either thermoplastics or thermosets. The former exists as single discrete long-chain molecules whereas the latter has a cross-linked network structure. The properties of plastics are considerably different and they depend on factors such as chemical structure, composition, thermal history and the manufacturing conditions.
Aims
¢ Characterise the physical properties of six common plastics
¢ Fabrication of plastics and composites
¢ Evaluate the hardness, strength and creep properties of various plastics or composites
¢ Establish the identity of six common plastics
Samples
¢ Teflon, polypropylene, cellulose fibre reinforced epoxy composite
¢ PMMA, polyvinyl chloride, polyethylene
Experimental Procedure
In this lab you will be provided with six unknown plastic samples numbered from 1 to 6. Your task is to conduct a series of tests described below which will assist you to establish the identity of each of the six plastics.
Test 1: General Characteristics
??Colour and texture
??Transparent or opaque
??Rigid or flexible.
??Amorphous or semicrystalline
Test 2: Density Measurements
(a) Direct method
Density =D=Mass /Volume
(b) Archimedes method
Density =D=(Ml /M2 -M3 )D1
M1 = mass of dried specimen
Di = density of immersion liquid
M2 = mass of specimen, saturated with liquid and suspended in air
M3 = mass of specimen, saturated with and suspended in liquid
Test 3: Water Absorption
Water uptake (%) = (M2-M1 /M 1 ) Ã100
M2 = mass of specimen saturated with liquid
M1 = mass of dried specimen
Test 4: Burning Test:
Observe the following characteristics:
¢ colour of flame
¢ melting or non-melting
¢ dripping or non-dripping
¢ whether non-burning, self-extinguishing, fast or slow burning
Test 5: Indentation Test
Measurement of the resistance of plastics to indentation or hardness. High hardness implies a high resistance to deformation of the plastics.
Test 6: Indentation Creep Test
All plastics are viscoelastic and thus will deform with time, i.e. creep. The creep resistance of a plastic can be measured by evaluating its hardness variation with time.
Test 7: Strength Test
Measurement of the resistance of plastics to breaking or bending. A three-point bend test will be performed to measure the flexural strength of selected plastics.
Report:
Describe in detail the methodology used in the characterisation and testing of the various plastic samples. Discuss and comment on the physical meaning and significance of the results obtained for each test. Compare the measured values with the literature values and comment on the accuracy of the values obtained. Establish the identity and chemical structure of the various plastics by completing the table below:
Sample Number Thermoplastics or thermoset Identity of plastic Chemical structure
1
2
3
4
5
6
