write a list of precautions required for
conducting
experiment to &dentify thermoplastic,thermosetting by flame set
Answers
Experiment No :1
Identify thermoplastic and thermosetting plastics by flame test.
Materials And Equipments Required:
• Tong.
• Bunsen Burner.
• Plastic samples.
• Beakers,etc.
Principle:
The experiment is based on the property of plastics.The plastic when expressed to heat if the sample is being softened and can be stretched easily,it is the thermoplastic.If the sample burns with a burning smell,it is thermosetting.
Thermoplastic:
A plastic which will soften when heated and harden when cooled.A thermoplastic, also known as a thermosoftening plastic, is a polymer that turns to a liquid when heated and freezes to a very glassy state when cooled sufficiently. Most thermoplastics are high-molecular-weight polymers whose chains associate through weak Van der Waals forces or even stacking of aromatic rings. Many thermoplastic materials are addition polymers; e.g., vinyl chain-growth polymers such as polyethylene and polypropylene.
Plastic flow takes very readily due to heating of their structure,which breaks the secondary bonds between the individual chains.Most thermoplastic consists of very long chains of carbon atoms covalently bonded together.In thermoplastic the long molecular chains are bonded to each other by seconday bond. Thermoplastics are recyclable materials that are used frequently today to create objects such as foam cups, polyethylene squeeze bottles, acrylic lenses and safety helmets. Their unique properties set them apart from the other two types of plastic, thermosets and elastomers. Heat and pressure cause the molecular structure of a thermoplastic to change, making it pliable and more useful.
Thermoplastics are the only type of plastic that can be welded. When heated to about 120 to 180 degrees Celsius, thermoplastics become pasty or liquid, and they can be molded and formed into different shapes. Each type of thermoplastic has its own properties, characteristics and welding temperature. They can withstand multiple heating and re-shaping, which makes them recyclable. Once the thermoplastic object has cooled down, the new form is set.Types of thermoplastics include polyethylene (PE), polyvinyl chloride (PVC) and polystyrene (PS), which often are used for packaging. Other groups of thermoplastics are acrylics, fluoropolymers, polyesters, polyimides and nylons. All of these types can be melted down many times and re-shaped into different forms. For example, a foam cup is a thermoplastic material that can be heated and turned into a dish.
Thermosetting:
Thermosetting plastics are simply plastics when moulded into shape and allowed to cool will not change shape when heated again they will char or burn an example of a thermosetting plastic is urea formaldehyde.These plastics have their dimensional network structures with predominantly covalent bonding. Thermosetting, plastics are synthetic materials that strengthen during being heated, but cannot be successfully remolded or reheated after their initial heat-forming.
Thermoset plastics differ in that they are not re-mouldable. Strong cross links are formed during the initial moulding process that give the material a stable structure. They are more likely to be used in situations where thermal stability is required. They tend to lack tensile strength and can be brittle.Once the curing process is complete,these plastics cannot be softened or reworked.
Some examples of thermosets are:
• Polyester fibreglass systems: (SMC Sheet molding compounds and BMC Bulk molding compounds).
• Vulcanized rubber.
• Bakelite, a phenol-formaldehyde resin (used in electrical insulators and plasticware).
• Duroplast, light but strong material, similar to Bakelite (used for making car parts).
• Urea-formaldehyde foam (used in plywood, particleboard and medium-density fibreboard).
• Melamine resin (used on worktop surfaces).
• Epoxy resin (used as the matrix component in many fibre reinforced plastics such as glass reinforced plastic and graphite-reinforced plastic).
• Polyimides (used in printed circuit boards and in body parts of modern airplanes).
• Cyanate Esters or Polycyanurates for electronics applications with high demands on dielectric properties and high glass temperature requirements in composites.
• Mold or Mold Runners (the black plastic part in Integrated Circuits (IC) or semiconductors).
Procedure:
1. Take different samples of plastics and label them A,B,C.
2. Take sample A and clamp it in the tong.
3. Place the sample on Bunsen flame.
4. Observe the burning of sample.
5. Note the observation that whether sample are being softened or decompose.
6. Repeat procedure with other samples.
7. Record the observations.
Observations:
Sample No. Nature of Plastic
(Thermoplastic/Thermosetting)
A Thermoplastic
B Thermoplastic
C Thermosetting
Answer:
While doing this activity if needed cover your nose and mouth with a mask to avoid breathing fumes. And also keep yourself away from spirit lamp flame by stretching your hand....
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