Recylcable Plastics

type 1 plastic name

PET / PETE

Poly(ethylene terephtate)

PET / PETE

• poly(ethylene terephtate)

• plastic used to package majority of soft drinks, liquor bottles, peanut butter jars, and edible-oil bottles

• ¼ of plastic bottles

• clear, tough, hold CO2 well

• easiest to recycle

which type of plastic is easiest to recycle?

type 1 - PETE

type 2 plastic name

HDPE

High - density polyethylene

HDPE

• high-density polyethylene

• largely linear form of polyetylene

• over 50% of plastic bottle market

• contain milk, juices, butter, grocery snacks

• easily formed thru application of heat & pressure 

• relatively rigid and low cost

• often includes color → reduces value of recycled plastic

why does color matter in plastics?

decreases value of recycled material

type 3 plastic name

PVC or V

poly(vinyl chloride)

PVC

• used pure or as blend to make variety of products

• products = PVC pipes, food packaging film, containers for window cleaners, edible oils, & solid detergents

• only 5% of container market

• white, so color is not an issue

• increased hazards due to Cl (when heated, releases Cl radical)

type 4 plastic

LDPE

low-density polyethylene

LDPE

• type 4

• low-density polyethylene

• has branching → less crystalline, more flexible, less strong than HDPE

• greater amorphous character → more porous than HDPE

• inert barrier to moisture

• major material for films for trash and bread bags

• requires special facilities to recycle

is HDPE or LDPE stronger?

HDPE

is HDPE or LDPE more flexible?

LDPE

type 5 plastic

PP

polypropylene

PP (polypropylene)

• type 5

• good chemical & fatigue resistance

• used to make film & fibers

• few containers use it

type 6 plastic name

polystyrene (PS)

PS

• type 6

• polystyrene

• used to make wide variety of containers, including styrofoam things, yogurt containers, egg cartons, meat trays, plates

• hard to recycle due to high MP (over 200)

why are type 6 polystyrene plastics so hard to recycle?

they ahve a high MP (over 200 degrees C)

type 7 plastics name

“other plastics'“

catch all

describe other plastics

• type 7

• wide variety coming to market including copolymers, blends, and multilayered combinations

• hard to recycle

describe common characteristics of recyclable plastics

• mostly packaging

• 1 polymer each

• mostly thermoplastics

why are containers and packaging the most recycled plastic?

they are usually 1 polymer and can be melted

why can’t all polymers be recycled the same?

• different melting points

• bags/thin films can’t be processed in traditional recycling streams

• some products make plastic packaging more dirty (ex. styrofoam meat trays)

most widely used plastic recycling system in the US

mechanical recycling

mecanical recycling was designed for…

rigid bottles

• not films/multi-layer materials/composites/copolymers

steps of mechanical recycling

1. collection

2. sortation

3. mechanical grinding/shredding

4. regranulating

collection phase of mechanical recycling

• one of the hardest steps

• only 17% of recyclable materials are collected

sortation phase of mechanical recycling

• requires immense amt of labor

• often by hand, assisted by technology

what is done before/after mechanical grinding/shredding phase of mechanical recycling?

washing

regranulating phase of mechanical recycling

use heat and pressure to melt & extrude new pellets & fibers

polymers from mechanical recycling are _________

downgraded

• the quality of recycled pastic is never as good as new plastic

the quality of recycled pastic is ________ as good as new plastic

never

many #1 PET bottles get turned into _________, not new bottles

polyester clothing

the US is building its own capacity for mechanical recycling, but we stil…

ship some materials over sea

3 types of advanced recycling techniques for plastics

1. pyrollysis

2. gasification

3. molecular/chemical recycling or depolymerization

pyrolysis

• used, mixed plastics are heated (300-400 degrees C) in absence of oxygen (inert atm) until thermally decomposed

• condensed into pyrolysis oil (pyoil)

pyoil

pyrolysis oil; product of condensing used, mixed plastics and heating them in the absence of oxygen

what is produced in addition to pyoil in pyrolysis?

• gas

• char

what happens to gas produced in pyrolysis

may be burned to power recylcing plant

what happens after pyoil is produced?

it is shipped to oil processing facilities & combined with crude oil from earth

existing technologies are used to separate pyoil and crude il into their _________ fractions

component

• short/long chain alkanes

one barrel of pyoil essentially replaces _____ barrel of crude oil

1

oil producing facilities are often _________ and synthesize _______ materials

manufacturers / raw polymer

does pyrolysis lead to downgrading of new polymers?

no

gasification

• used plastics are heated in an oxygen-controlled atm and converted into syngas (H2 and CO)

• syngas is feedstock for methanol and liquid fuels

• can take mixed plastic waste

syngas

• H2 and CO

• produced in gasification

can gasification take mixed plastic waste?

yes

can pyrolysis take mixed plastic waste?

yes

molecular / chemical recycling or depolymerization

• chemical reactions to remake original monomers

• especially good for colored plastics

• cana only do 1 type of plastic at a time

• requires solvent