Chem300A L9 20.ppt - University of Victoria
Transcript of Chem300A L9 20.ppt - University of Victoria
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Materials
Plastic: material that can be molded or shaped
Polymer: macromolecule = material of high molecular weight,formed from many repeating units
• Mostly from petrochemicals• Widely used: rubber, insulation material, fibers, paint, foams,
adhesives, molds, structural material
1. Plastics and Polymers
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Thermoplastic: material that softens when heated, sets when cool
Thermoset: material that is soft enough to be molded when made but permanently sets on heating
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Properties of Polymers depend on their molecular structure
Order in which the monomers are arranged:
Homopolymers: A‐A‐A‐A‐A‐A‐A‐A‐A‐A
Copolymers: A‐B‐A‐B‐A‐B or A‐A‐A‐A‐B‐B‐B‐B‐A‐A‐A‐A
Three‐dimensional arrangement withinthe chain:
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Linear vs. branched
Low density polymer low melting flexible plastic
High density polymerdenser and more rigid plastic
The Extraordinary Chemistry of Ordinary Things, 4th Ed.
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Rigidity is provided by crystalline region
Fibers can be drawby extruding moltenpolymers (Nylon, Dacron, polyethylene)
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Elastomers: materials that can be deformed and revert back to original form when deformation force is removed
E.g. rubber
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Types of synthesis to bring monomers together
Addition reaction: A• + A –> A‐A• + A ‐> A‐A‐A•
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radical
cationic
anionic
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Addition reactions: different products if monomer is non‐symmetrical
Chemistry in Context 6th Edition, ACS, McGraw‐Hill
Polyvinyl chloride (PVC)• tough• insulating• heat sensitive
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dominant
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Condensation reactions: X‐A‐X + Y‐B‐Y –> X‐A‐B‐Y + XY
PET = Polyester = polyethylene terephthalate
Chemistry in Context 6th Edition, ACS, McGraw‐Hill
Similar for polyamides like Kevlar: N2N‐Aryl‐NH2 + HO2C‐Aryl‐CO2H
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The Extraordinary Chemistry of Ordinary Things, 4th Ed.
Bakelite (1909):Phenol‐formaldehyde resinwith wood ‘flour’ also usedto bind plywood layers
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Ring opening polymerizations
E
Oacid or base
catalystE
O
n
E = O = caprolactoneE = NH = caprolactam
E = O = polyesterE = NH = polyamide (nylon-6)
acidcatalystO
OO
n
polyethylene glycol (PEG)
PEG used in surgical applications and can be ingestedPegylation is attaching PEG polymers to drugs to improve pharmacokinetics
Water-soluble
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Ring opening polymerizations: Epoxy Resins
O2
OH
acidHO OH
Bisphenol-A
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Ring opening polymerizations: Metathesis (ROMP)
Metal‐alkylidenes are capable of exchanging =CR2 ends of alkenes:
If we use cyclic alkenes we get polymerization: CD blanksNon‐fog plastics
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Synthetic rubber, 1839: Charles Goodyearaccidentally dropped a mixture of rubber and sulfur on a hot stove:mixture was nicely elastic – vulcanized rubber
wikipedia
The Extraordinary Chemistry of Ordinary Things, 4th Ed.
Synthetic Polymers
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Synthetic elastomers: styrene‐butadiene rubber (75:25 btd/sty)
Neoprene
The Extraordinary Chemistry of Ordinary Things, 4th Ed.
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Most popular polymers and their recycling codes: ‘The Big Six’
Chemistry in Context 6th Edition, ACS, McGraw‐Hill
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Chemistry in Context 6th Edition, ACS, McGraw‐Hill
Most popular polymers and their recycling codes: ‘The Big Six’
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Plastic recycling codes in summary
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Plasticizers: lubricants between the chains to soften polymers: PVC
PVC food wraps contain other plasticizers such as adipates and citrates
Bis(2-ethylhexyl) adipate – DEHAShown to induce liver cancer in mice but not rats: controversial
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Other major polymers
The Extraordinary Chemistry of Ordinary Things, 4th Ed.
2020
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Nylon 6,6
The Extraordinary Chemistry of Ordinary Things, 4th Ed.
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Polyethylene terephthalate: PET
The Extraordinary Chemistry of Ordinary Things, 4th Ed.
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ABS ‐ AxBySz
15% ‐ 35% ‐ acrylonitrile
5% ‐ 30% ‐ 1,3‐butadiene
40% ‐ 60% ‐ styrene
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• Tough• Insulating• Injection moldable• Used in: protective equipment,
car parts, bottle caps, etc.
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Polycarbonates
Usually with bisphenol‐A
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• Heat resistant• Insulating• Flame retardant• Used in: circuit boards, CD blanks,
formerly water bottles, containers
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Food packaging: not biodegradable and not recyclable – yet?
Barrier films are laminates of many layers: 7 or more commonEach layer has its purpose:• Low oxygen permeability (nylon)• Low moisture permeability• Toughness (polypropylene, HDPE)• Printable
New fully compostable Food barrier film from BASF
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Recycling
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Typical municipal wastes US
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2015 World Recycling Data (Source: OECD (2015), “Municipal Waste”, OECD Environment Statistics)
Canada 24% recycling rate (places us in the bottom 1/3)US 35%Europe 40%Germany 65%
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Fate of the non‐recycled plastics: dump or incineration
Potential solutions:
Biodegradable plastic (see next slides)• monomers that decompose over time (e.g. with moisture)• smaller chains are degraded by bacteria to CO2 + H2O
Incineration• plastics account for up to 30% of waste energy content = fuel?
Issues:• chlorine based polymers release HCl• toxic chemicals• metals in ink in ash (Pb, Cd)
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Biodegradable Polymers: the way forward?
Alkyl esters: much more easily hydrolyzed than PET
Polyhydroxyalkanoates (PHA)
OO
On
• Monomers from bacterial fermentation of sugars
From: Biopact.com
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Polylactic acid (PLA)
OO
O
nCH3
HOOH
O
CH3O
OO
CH3O
H3Clactic acid
lactide
PLA
• Monomer from corn starch or sugarcane
• Degrades quickly• Easily recycled by thermal
depolymerization or hydrolysis
Largest manufacturer in US:NatureWorks (Cargill)
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Polyanhydrides
• Anhydrides are quite easy to hydrolyze• Rapid breakdown in wet environs• Biocompatible: drug delivery
University of Washington Engineering
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Cellulose Derivatives
Cellulose nitrate
• Extremely flammable• Used for movie film until 1948• Soaking cotton in nitric acid gives the highly
flammable ‘guncotton’ (below)• Used for artificial ‘ivory’ in 19th century (right)
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Cellulose Derivatives
Cellulose acetate
• Replaced cellulose nitrate film• Used in computer tape• Breaks down with heat, compostable• Fibres highly desirable for clothing: breathable, dries quickly, no static cling,
soft, easily dyed and retains bright colours well
Carpet fibre and backingAcetate film Rayon fibres
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Recycling:
• Collection• Transportation• Sorting• Melting – used directly or pelletized for future use
Recycled‐content product: materials would have been waste
Post‐consumer content: material previously used and recycled
Pre‐consumer content: material that was waste (scraps, clippings)
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Sorting by density
Chemistry in Context 6th Edition, ACS, McGraw‐Hill
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From: Canadian Plastics Industry Association website
For an example of acompany that specializes inrecycling plastics see:www.postplastics.com