polymerisation

• polymerisation is the process by which monomers join together to form polymers
• a polyunsaturated food substance contains more than one carbon carbon double bond
• the hydrogenation of vegetable oils involves heating them with nickel catalyst at high pressure, this converts unsaturated fats into saturated fats
• hydrogenation is used to convert unsaturated oil to saturated fats
• polyunsaturated fats contain hydrogen chain with 2 more carbon carbon double bonds in each chain
• saturated fats are solid at room temperature
• saturated fats have a higher melting point
• unsaturated oil is liquid at room temperature
• unsaturated oils has a lower melting point
• a polymer is a large organic molecule built up from multiple small units called a monomer
• natural polymers: DNA
• manmade polymers: polyethene, nylon
• polymers are bonded by covalant bonds
• what is addition polymerisation?

  a type of polymerisation which occurs when unsaturated monomers join together without loosing any molecules or atoms
• ethene can undergo addition polymerisation to form polyethene in the presence of a catalyst, at high temperature and pressure
• at high temperature & pressure and when a catalyst is present, the carbon carbon double bonds in ethene molecules break open and form a long chain. each monomer is bonded by 2 other monomers
• uses of polyethene


  cling wrap, plastic bottles
• before the recycling of polyethene, it needs to undergo pre-treatment. what happens during pre-treatment?


  sorting Is done. clean them to remove contamination and shred plastic to smaller pieces
• physical method used to recycle polyethene

  melt the plastic, cool it down, pull them into long strands and cut them into smaller pieces
• chemical method used to recycle polyethene

  cracking of the larger hydrocarbons into smaller short chain alkanes and alkenes
• why do plastics cause pollution and must be recycled?

  most plastics are bio-degradable meaning that they cannot be broken down by living organisms or bacteria. thus, the biggest problem is how we choose to dispose them after use
• land pollution of plastics

  plastics do not break down. this leads to a build up of waste when plastics are buried in landfills
• air pollution of plastics


  combustion of certain plastics releases toxic gas into the atmosphere
• water pollution of plastics


  if plastics are thrown into the sea, can harm aquatic life. plastics can also clog up rivers and drains which in turn, creates breeding grounds for mosquitoes
• one molecule of polyethene can contain more than 10,000 molecules
• polymers have high melting points because there are many strong covalent bonds between the atoms within the long chains
• vegetable oils are polyunsaturated because they have not undergone hydrogenation
• hydrogenation involves adding hydrogen to double carbon-carbon bonds using nickel as a catalyst
• hydrogenation is used to make unsaturated fats saturated in the presence of a nickle catalyst at high temperature
• the process of making margarine from vegetable oil is called hydrogenation
• advantage of being non biodegradable

  its highly durable
• disadvantage of being non biodegradable

  causes land pollution as it cant be broken down easily