ch 8- polymers Flashcards
addition polymerisation
chemical reaction between monomers resulting in the formation of a polymer
alkene
hydrocarbon with at least one double carbon to carbon bond
alkyne
hydrocarbon with at least one triple carbon to carbon bond
condensation polymerisation
chemical reaction between monomers resulting in the formation of a polymer and water
cross link
covalent bond between polymer chains
thermosetting-cross linked polymers
polymer with covalent bonds/cross links that degrade or char when heated
elastomers
polymer that forms occasional cross links and is elastic
functional group
specific groups of atoms within a compound that affect the properties of the compound
high density polyethene HDPE
tightly packed polymers produced at lower pressures
linear- thermoplastic polymers
polymer with no cross links that can be remoulded when haeted
low density polyethene LDPE
branched polymer produced at high pressures
monomers
molecules that can react with other molecules to form larger molecules
plastic
molecule produced synthetically from monomers bonded together
polymer
molecule produced naturally or synthetically from monomers bonded together
general formula for addition polymerisation
[C=C + C=C]n
->
-[-C-C-C-C-]-n
general formula for condensation polymerisaiton
let R= any group where a carbon or hydrogen is attached to the rest
R-A-H + R-B-OH
->
R-A-B-R + H2O
how does addition polymerisation work
the C to C double or triple bond is broken, allowing carbon atoms to form bonds with adjascent monomers
how does condensation polymerisation work
two functional groupds react to form a bond between monomers- forming a polymer and water
general formula for the formation of polyesters
(n+1) R(OH)2 + n R’(COOH)2 → HO[ROOCR’COO]nROH + 2n H2O
polymer properties
light and strong
durable
highly versatile and modifiable
flammable
chemically resistant- particularly against acids
effective thermal and electrical insulators
polar vs non polar polymers
non polar monomer are only held together by dispersion forces but when a polymer
non polar polymer- tetrafluoroethene
polytetrafluroethene has strong dispersion forces between chains and other substances making it non stick
polar polymer- polyacrylonitrile
make materials like carbon fibre which is found in tennis raquets and fishing rods.
the carbon nitrogen bond in acrylonitrile- the monomer, creates permanent dipole-dipole interaction between chains, giving them a high tensile strength and stiffness
what determines the properties of a polymer
the monomer itself
the size and branching - the greater the chain length, the stronger the inermolecular forces due to greater surface material ( the strong intermolecular forces make the material tough)
polarity- physical properties of polymers as it creates certain attractions
how is low density polyethene produced
when polymerisation occurs at high temperatures and high pressures, polymers are unable to form linear chains
LDPE has many branches that extend from the parent chain
how do the branches prevent LDPE from becoming dense
the branches prevent them from packing close together, leading to weakened dispersion forces
LDPE properties
- Lower density (relative to DPE)
- Relatively soft
- Lower melting point (105115 C) (relative to DPE)
- Good chemical resistance
- generally opaque
how is high density polyethene produced
HDPE is produced under lower temperature and pressure conditions
little brancing and the polymer chains can pack together tightlyp
HDPE properties
higher density (relative to LDPE)
* hard
* higher melting point (120180 C) (relative to LDPE)
* Weatherproof and cold-resistant
* Good chemical resistance
* Allows light to pass through
* Insulator of electricity
polypropene- type of polymerisation
addition
polypropene- properties and applications
durable and cheap making it good for artificial turf and rope
polyvinylidene chloride- type of polymerisation
addition
polyvinylidene chloride- properties and applications
sticks to itself, making it good for food wrap
polyamide/nylon- type of polymerisation
condensation
polystyrene- type of polymerisation
addition
polystyrene- properties and applications
can be solid or foamed and can be used in cups, insulation foam or bean bags filling
linear polymers properties
when heated, they soften enabling them to be reshaped or remoulded
commonly sold as pellets that are heated then moulded to make a variety of plastics
intramolecular bonds of linear polymers are much stronger than the intermolecular forces holding the chains together
sufficient exposure to heat, individual chains become mobile and the plastic can be reshaped
how does the presence of cross links impact a molecule
it greatly restricts the movement of a molecule, making it more rigid and heat resistant
do thermoplastics have cross links
no
forces between chains in thermoplastics
weak intermolecular
thermoplastics- response to heat
softens/melts
thermoplastics- hardness
varies
elastomers- cross links
a few giving them elasticity
elastomers- forces between chains
weak intermolecular forces and occasional strong covalent bonds
elastomers- response to heat
varies- stretch and return to original shape
elastomers- hardness
varies
thermosets- cross links
larger number
thermosets- forces between chains
strong covalent bonds
thermosets- response to heat
degradation and decomposition
thermosets- hardness
generally hard
biodegradable
not to be confused with compostable
ability to decompose in the environment
within a given time frame (~80 years is a good ballpark)
bioplastics
plastics produced from biomass
carbon negative
describes a process that absorbs more carbon dioxide than it produces
chemolysis
the use of solely chemical substances to decompose organic substances into simpler ones
circular economy
A continuous cycle that focuses on the optimal use and re-use of resources from the extraction of raw materials through to production of new materials, followed by the consumption and re-purposing of unused and waste materials
compostable
Describes a polymer that can be at least 90% decomposed after 180 days in a composting environment
dehydrate
To remove H₂O from a molecule or ion
dehydrogenate
To remove a hydrogen atom or atoms from a molecule or ion
feedstock
raw material used for producing another product
greenhouse gases
molecules that absorb infrared radiation from the sun
humus
dark, nutrient-rich, organic material produced from composting
linear economy
Operates on a ‘take-make-dispose’ model, making use of resources to produce products that will be discarded after use
plastic dissolution
dissolving plastic to extract polymers and separate them from their additives
pyrolysis
decomposition brought about by high temperatures
steam cracking
The breaking down of larger saturated hydrocarbons into smaller, often unsaturated ones
how is ethene produced
via steam cracking- larger hydrocarbons extracted from crude oil, are mixed with steam and heated in the absence of oxygen to produce small, unsaturated hydrocarbons.
what is HDPE used in
milk jugs, detergent bottles, outdoor furniture
what is LDPE used for
plastic bags, food wraps
PVC
aka vinyl
widely used plastic made up of chloroethene/vinyl chloride monomers
chloroethene monomers are synthesised by reacting chlorine gas with ethene which is produced from crude oil in steam cracking
what is PVC used for
pipes, electrical cable insulation, vinyl records
PP
plastic composed of propene monomers that are produced via steam cracking
PP applications
flexible, rigid packaging, rugs, bags, cars
PS
distinctive plastic made of styrene monomers
ethyl benzene is dehydrogenated and then polymerised
PS application
as it is soft and lightweight, it is suitable for usage in packaging, polystyrene cups and insulated boxes
PLA
polylactic acid is a condensation polymer produced from fermented plant starch from crops like sugarcane or corn
PLA properties
low melting point
high strength
good adhesivity
most widely used filament plastic in 3d printing- also used in disposable cutlery
bio PE
bio polyethene/renewable polyethene has the same formula as HDPE and LDPE but is deribed from plants
how is bio PE produced
crops are fermented to produce ethanol which is then dehydrated to form ethene and polymerised and can be produced as LDPE or HDPE
bio PE environmental impacts
crops used to produce bio PE like wheat and sugar cane, absorb carbon dioxide making its production carbon negative, reducing greenhoue gas emissions
howver, it requires a large area and rapid harvesting can cause land degradation
bio PP
bio polypropene is primarily produced from crops or vegetable oils
production of bio pp from crops
fermentation (methylpropan-1-ol)
dehydration (methyl propene)
various methods (propene)
addition polymerisation (polypropene)
same manufacturing equipment can be used
recycling codes
1- PETE
2- HDPE
3- PVC
4- LDPE
5- PP
6- PS
7- other
mechanical recycling process
collection
sorting
cleaning
shredding
melting
reforming
repurposing
can thermosets be recycled
in general they can’t but all thermoplastics can be mechanically recucled
products of mechanical recycling
usually only used for lower grade plastic products due to hte risk of toxic contamination and some plastics like PVC are more difficult and resource intensive to recycle than others and so not all recycling facilities consider recycling worthwhile
chemical recycling
aka advanced or feedstock recycling involves converting plastics back into either constituent polymers, monomers or organic chemicals
how can chemical recycling occur
plastic dissolution- heating plastics with solvents to produce a solution of polymers and additives that can be separated
chemolysis- depolymerising plastics breaking it up into its constituent monomers- only used for condensation plymers
pyrolysis- convert plastics to raw organic chemicals which can then be used as fuels to produce energy- prohibitvely expensive
chemical recycling methods and products- conversion
methods: conversion
- gasification, pyrolysis, hydrothermal, hydrocracking
products
- refined hydrocarbons give you petrochemicals or fuels -> monomers -> polymers -> plastic products
chemical recycling methods and products- polymerisation
methods:
enzymolysis
chemolysis
solvolysis
products
monomers -> polymers -> plastic products
chemical recycling methods and products- purification
method:
dissolution
products
polymers -> plastic products
compostable plastics
biodegradable in a short time period without leaving any toxic residue or microplastics only nutrients
process of degrading compostable plastics
bacteria in a composter struggles to break down the polymer chains- so it is first shredded
reacted with water at high temperatures to break it down into its constituent monomers
bacteria decompose the monomers to produce water vapour and CO2- released into environment as well as humus
high temperature environments of an industrial composter to break down rapidly - in these composting environments, moistre, oxygen and heat levels are carefully controleld to ensure maximal breakdown rate
examples of compostable bioplstics
PLA and PHB (polyhydroxylbutyrate)- produced when microorganisms are stressed
PHB can be used for internal stitches as it is non toxic
fossil fuel based plastic that is compostable
PBAT- polybutylene adipate terephthalate is tough and flexible that can be used to make cling wrap
current barriers to plastic recycling
25%- of thermoset plastics cant be recycled
recycling is expensive and buyers of recycled plastics are hard to find
insufficient recycling facilites- shipped overseas prior but this is now banned
incineration is cheaper- produces toxic emissions
only 9% is actually recycled
potential circularity of chemical recycling
monomers
polymerisation
high grade plastic
chemical recycling
monomers
condensation polymerisation
chemical reaction between monomers resulting in the formation of a polymer and water
hydrolysis
reaction involving the cleavafe of bonds using water to break up polymers into monomers
innovation
introduction of new methods, procedures or products to traditional industries
in condensation polymerisation what reacts
alcohol with another functional group, often a carboxylic acid to form a covalent bond bewteen molecules, simultaneously releasing a water molecule
uses of PLA
as it can be degraded into lactic acid, it is useful in the construction of medical implants like screws or plates as it can remain intact for up to 2 years during a healing process before being broken down and naturally removed
condensation polymerisation for PBS- polybutylene succinate
monomer succinic acid (COOH functional group) + monomer 1,4 butanediol (OH functional group)
-> polybutylene succinate + water
what makes polymers biodegradable
as condensation reactions produce water, due to he rearrangement of oxygen and hydrogen atoms from functional groups into water molecules- the functional groups are left in a reactive state
when water is reintroduced to the polymer system- the reaction occurs in reverse, through hydrolysis
polymer circular economy
renewable resource
industrial processing plant
biodegradable polymer product
biowaste bin
specific biowaste collection
biowaste treatment composting plant
fertiliser
back to a renewable source
how does stronger intermolecular forces impact the properties of the polymer
increase hardness and rigidity of the polymer
increase melting point or density as they are held together tightly
3 ways bioplastics can be recycled
chemical- polymer to monomers to raw chemicals
mechanical- shred, melt, reform
organic- composters
difference between natural and synthetic polymers
Natural polymers are created in the environment, for example, by plants or animals.
synthetic polymers are man-made through manufacturing processes.
