material choices Flashcards
what are properties of materials?
unvulcanised rubber - low tensile strength - erasers
vulcanised rubber - high tensile strength - care tyres
plastic, polythene - low density, easy moulded - plastic bag
plastic, polystyrene - low density, stiff - coffee cups, egg cartons
synthetic fibres, nylon - low density, waterproof - clothing, ropes
synthetic fibres, polyester - low density, waterproof - bottles
how is crude oil separated by fractional distillation?
1) oil heated
2) vapour passes into column near bottom and cool as it rises
3) each fraction condenses to liquid and runs when cooled below boiling point
4) remaining gases leave tower + used as gaseous fuels
how can you explain boiling points?
intermolecular forces - forces between mols that hold mols together in a solid or liquid
1) longer the hydrocarbon mol, stronger the force
2) stronger forces need more energy so a higher temp is needed to boil the longer hydrocarbon fractions
what are natural materials?
from living things which need little processing eg cotton and paper
raw materials - extracted from earths crust, limestone and crude oil
why are synthetic materials replaced with natural materials?
- natural materials short in supply
- cheaper and made in quantity needed
what is crude oil and using hydrocarbons?
crude oil = made from hydrocarbons
making polymers and what is polymerisation?
polymer = large mol made by small mol -> monomers
polymers are made by polymerisation
ethene = monomer to make polyethene
H H H H H H H H
c=c + c=c —-> -c- c- c -c-
H H H H H H H H
PET = pol 2 make drink bottles, strong, low dens, doesn’t shatter
what is the use of nanoparticles?
silver nano kill bacteria
nanoparticles modify properties eg:
- silver nano give fibres in clothes antibacterial properties
- carbon nanotubes to sport equipment, stiffer and strong
what are nanoscale particles?
3 answers
- occur naturally eg sea spray
- occur by accident eg particulate carbon when fuel burns
- made by scientists
how can we improve polymers?
- increasing chain length makes it stronger
- plasticisers make pol softer, weak force between
pol chains - crosslinks, atoms bonding bet pol mol, harder and strong eg vulcanisation when sulfur atoms form cross links between rubber mol eg car tyres
- plasticised PVC, rain coats
- unplasticised PVC window frame
are nanoparticles safe?
silver nan get into sewage + may kill bac from washed clothes
if released, kill useful micro
used in sunscreen
small to pass through skin to blood, risk unknown
fear of lung or brain damage if breathed in
ppl say no threat bc occur naturally
whats polymer difference?
made with properties
LDE long molecular with branches which keep molecular chains apart so force is weak eg plastic bags
HDP long chains no branches so mol close. stronger water pipes etc and high crystallinity
