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Chapter 23: Environmental Aspects of Plastics

Professor Joe GreeneCSU, CHICO

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Topic• Source Reduction• Recycling• Regeneration• Degradation• Landfill• Incineration• Total Product Life Cycle• Future• Chemical Hazards• Sources of Chemical Hazards• MSDS

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Topic• Source Reduction

– Reduce the amount of material that is used in any application• Combine parts into larger parts, e.g., 1 liter soda uses 40% less

packaging than (2) 0.5 liters• Reduce thickness of plastic part, e.g., trash bags had 0.08mm thickness

(0.003 in) with LDPE, was reduced to 0.025mm (0.001 in) thickness with stronger and tougher LLDPE

• Reduce thickness by process imporvements• Substitution of plastics for paper have reduced weight of packaging

– 1000 grocery bags from paper weighs 140 lbs and stacks 46 inches– 1000 grocery bags from plastic weighs 15.6 lbs and stacks 3.5 in

– Recycle in house plastic from sprues and runners back into product.

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Topic• Recycling

– Collection: plastic listed with recycled number– Codes for plastics

• 1 PET• 2 HDPE• 3 Vinyl/PVC• 4 LDPE• 5 PP• 6 PS• 7 Other

– Handling/Sorting• Maximum economic is obtained when each material is sorted• Aluminum must be separated from metals since it can’t be readily separated

from zinc and brass• Plastics are sorted mostly by sight. Machines can sort by light absorption

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Topic• Recycling

– Reclamation and Cleaning• Plastic is shredded and cleaned

– End-Uses- Sorted PCR (Post Consumer Recycle)• LDPE for new bags and film• PS in insulation and instrument packaging• PP in automotive parts, e.g., interior door inner panels, head liners, etc.• Mechanical properties drop with use of regrind plastic versus virgin

plastic. Max use of 50% regrind, Typical 20%.

– End-Uses- Comingled PCR with several plastics regrind• Other plastics include thermoset materials, elastomers, and composites• Plastic wood with use of comingled PCR that is compression molded

and not injeciton molded usually.

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Topic• Regeneration

– Process of breaking down polymer molecule into basic chemicals or chemical recycling.

– Easiest to regenerate is condensation polymers, PET and nylon.– Under high pressure and heat in the presence of a catalyst the

molecule unzips and regenerates the monomers.– Thermoset composites use process of pyrolysys, which is the

decomposition of a material using heat in the absence of oxygen.

– Advantage of this process is it is more effective for mixed plastics than PCR

– Disadvantages is the generation of air and water pollution and large amounts of energy required

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Topic• Landfills

– 90% of all solid waste (by weight) in US is sanitary landfill.– Plastics comprise 8 % by weight and 20% by volume.– Paper products comprise 40% by weight and 34% by volume.– Percentage of plastics in landfill has not grown in the last 20 years.

• Inceration– Controlled burning is an option for disposing of a large percentage

of municipal solid waste.– Paper, plastic, and other flammables are separtaed from solid

waste and pressed into pellets and burned at a separte facility.– Burning generates electricity– Environmental concerns includes creation of toxins (dioxins), ash

problems, and carbon dioxode releae for global warming

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Topic• Inceration

– Burning generates electricity– Energy content of various solid waste

Material Energy Value (BTU/pound)• PET 10,900• HDPE 18,700• Rubber 12,800• Newspaper 8,000• Wood 7,300• Yard Waste 2,900• Fuel oil 20,900• Coal 9,600

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Topic• Total Product Life Cycle

– What is the total impact of a particular product or product type on the environment over the total life cycle of the product from the creation of the product, its use, and disposal impact.

– Example,– Polystyrene versus paper cups, Table 23.3

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Topic• Energy Requirements

– Example,– Paper sack versus Polyethylene sack, Fig 23.3

– Refrigerators and freezers. Plastics are replace of glass and metal • Plastics saved 700 million pounds and require a total of 15.8 trillion BTUs

during production versus 23 trillion BTUs for metal and glass. (Savings of 7.2 trillion)

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Topic• Energy Requirements

– Plastic pipe• More tonnage of plastics hoes into pipe than any other single use.

– Weight of pipe was 2 billion pounds versus metal pipe of 17.5 billion pounds.

– Energy consumption of plastic was 84 trillion BTUs versus 408 trillion BTUs for metal pipe, Savings of 324 trillion BTUs

– Beverage Bottles• PET was introduced in mid 1970s to a market full of glass bottles.• Energy consumption for plastic is 18.2 trillion BTUs versus 24.2 trillion

BTUs for glass. Savings of 16 trillion BTUs, or equivalent to 2.8 millions barrels of crude oil.

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Chemical Hazards• Materials

– Resins (See MSDS)• Thermoplastic resins- low toxicity and low health hazard• Thermoset resins- moderate toxicity and moderate health hazard

– Reinforcements- low toxicity and moderate health hazards (dust)

– Fillers- low toxicity and moderate health hazards (dust)– Solvents- moderate to high toxicity with moderate to high

health hazards– Catalyst- moderate to high toxicity with moderate to high

health hazards– Plasticizers- low toxicity and moderate health hazards

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Material Safety Data Sheet(MSDS)

• Hazardous materials are common in the plastics industry

• MSDS are required to accompany any purchased hazardous industrial raw material.

• Plastics are defined as potentially hazardous because in the course of normal use, plastics may produce dusts, mists, gases, fumes, vapors, or smokes which are dangerous.

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Material Safety Data Sheet(MSDS)

• Section I: General Information• Section II: Composition• Section III: Physical Properties• Section IV: Fire and Explosion Hazard Data• Section V: Health Hazard Data• Section VI: Reactivity Data• Section VII: Spill or Leak Procedure• Section VIII: Occupational Protective Measures• Section IX: Special Precautions• Section X: Transportation

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Section I: General Information• Product name• Manufacturer’s Identity• Emergency telephone numbers• Trade name of chemical• Chemical family name of the material• Example

– Lexan– General Electric– 1-800-gecares– Lexan PC Resin– Poly(Bisphenol-A carbonate)– Chemical Abstracts Services (CAS) Number- Unambigous identification

of materials. Lexan= 25971-65-5 (same as Merlon)

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Section II: Composition

• Hazardous Ingredients– Major constituents– hazardous additives, fillers, or colorants– Example for ABS

• 3 % Carbon black (solid- trapped in polymer)• 0.2% residual styrene monomer (gas- released during

processing) CAS # Chemical

NameOSHAPEL Units

ACGIHTLV Units

763-86-9 Silica 0.05 mg/m3 0.05 mg/m3

100-42-5 Styrene 50.0 ppm 50.0 ppm1333-86-4 Carbon Black 3.5 mg/m3 3.5 mg/m3

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Section II: Definitions

• Definitions• OSHA- Occupational Safety and Health Administration• ACGIH- American Conference of Governmental Industrial Hygienists• PEL- Personal Exposure Limits (TWA) • TWA- Time weighted average. Exposure level considered acceptable

in an 8 hour day as part of a 40 hour week.• REL- Recommended exposure• TLV- Threshold Limit Value. Recommended by the American

congress of Governmental industrial Hygienist. (TWA for 8 hours)• STEL- Short term exposure limit. Acceptable exposure for 15 minutes

and should not be exceeded any time during the 8 hour work day.

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Section II: Styrene• Styrene as a health hazard

• Building block for thermoplastic styrenics, e.g., polystyrene, ABS, SAN, and others.

• Cross-linking building block for thermoset styrenics, e.g., polyesters, vinyl esters.

• ABS has 0.2 % residual styrene plus other sources (styrenic plastics)• One study found a range of 1 to 7 ppm styrene in an injection molding plant• Thermosets

– Manufacturing of large boat hulls, boats, large tanks, tubs, shower stalls, body panels for cars and trucks.

– Polyester is 35% styrene by weight.– Processing methods include fiber spray with resin in stream, handlayup

by roller, closed mold RTM operations, compression molding of polyester sheet.

• Ventilation is essential to keep exposure within limits.

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Section III: Physical Properties

• Properties of material as one substance– Evaporation Rate– Melting point– Boiling point– Specific gravity– Solubility in water– Physical form

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Section IV: Fire and Explosion Hazard Data

• Section for fire fighting• Most plastics are not explosive• Upon burning most plastics will yield water and CO2

• Many plastics are self-extinguishing • All thermosets are self-extinguishing • Water is recommended as the best medium for

extinguishing fires• Toxic fumes from plastics include

– black smoke, CO, hydrogen cyanide, and ammonia• Flash point is very high for many plastics

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Section V: Health Hazard Data

• Routes of entry of toxic substances– Ingestion

• Oral LD-50 in rats. Lethal Dose 50 percentile of fatalities in rats• Many pelletized plastics are rather inert.• Extremely toxic: LD-50 less than 1 mg/kg or 10 ppm• Highly toxic: LD-50 less than 50 mg/kg or 100 ppm• Moderately toxic: LD-50 less than 500 mg/kg or 1000 ppm• Slightly toxic: LD-50 greater than 500 mg/kg or 1000 ppm• Example

– LD-50 for guinea pig is 264mg/kg (264mg x mass of pig)– Assuming equal response from human: 264mg x 70kg for mass of

human = 18480mg or 18.48g to be ingested.

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Section V: Routes of Entry• Routes of entry of toxic substances

– Inhalation• Thermosets reactants can be inhaled since they are in liquid form and have a

vapor pressure that indicates relative volatility.• Example: Isocyanates used in polyurethane production

– TDI (toluene diisocyanate) used in foams for seats or paints.– MDI (methylene diisocynate) used in RIM body panels or in paints.– Construction projects use foamed polyurethane for interior walls and roofs. – TLV is 0.005 ppm– STEL for TDI is 0.02 ppm.

• Local and general ventilation are extremely important when working with urethanes

• Effects are asthma symptoms

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Section V: Routes of Entry• Routes of entry of toxic substances

– Inhalation• LC for lethal concentration (normally for a vapor or gas)• Unlikely for peletized plastics• Heated plastics yield hydrocarbons• Example

– Overheated PET releases acetaldehyde– STEL of 25 ppm– Odor threshold is 0.050 ppm.

• Example– PVD polymerization uses Vinyl chlorine gas– TLV of 5 ppm– Odor threshold of 3000 ppm (no odor warning)– Known human carcinogen

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Section V: Routes of Entry• Routes of entry of toxic substances

– Dermal (Skin)• Most pelletized plastics do not affect dermal• Isocyanates can cause rashes and blistering of skin• Isocyantes can cause discoloring of skin.• Hot plastic materials can cause skin burns• Catalyst materials can cause skin abrasions• Example

– Diethylene Triamine (catalyst) CAS# 111-40-0– ACGIH

» TLV STEL» 1 ppm (skin) NE

– OSHA» PEL STEL» 1 ppm NE

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Section V: Routes of Entry• Routes of entry of toxic substances

– Eyes• Injured by objects landing in the eye

– glass fibers, fillers, additives, colorants, particles of plastic– liquids and gases can cause severe damage– Example

» methylene- hardener for epoxy» Causes irreversible blindness in cats and visual impairment in cattle.

– Carcinogenicity• Pelletized plastics are often not regulated as carcinogenic• Residual monomers have links to cancer (vinyl acetate, a residual monomer from PVA and

EVA is present at 0.3%) at levels of 600 ppm caused some cancer in some animals (bears A3 notation)

• Some liquid polymers and catalysts can cause cancer in some animals

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Section VI: Reactivity Data

• Pelletized plastics are very stable and non-reactive• Thermo-oxidative degradation can yield hazardous gases

– PVC: at 100 ºC releases HCl– PMMA: at 100 ºC releases MMA– POM: at 230 ºC releases formaldehyde– Teflon (other fluoroplastics): at 250 ºC release HF – PET: at 300 ºC releases acetaldehyde– Nylons: at 300 ºC nylons release CO and ammonia– Nylon 6: at 340 ºC releases e-caprolactam– Thermoset resin degrade to toxic fumes of CO, formaldehyde, isocynates (for

urethanes)

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Section VI: Reactivity Data_PVC and POM• Thermal degradation of PVC

– PVC degradation is a serious problem• Can decompose catastrophically if overheated in barrel.• Remaining materials is tightly packed carbon• Fumes contain high concentrations of HCl• Response team must wear air respirator, turn off machine, tear down after cooling, remove nozzle and end cap.

• Thermal degradation of POM (poly actetal or polyoxymethylene)• Thermally degrades (>230 ºC )and releases formaldehyde• Exposure can occur at purging of machine• Local exhaust is essential to minimize exposure

• Thermal degradation of Phenolics• Major uses in adhesive applications (plywood & particleboard)• Compression and transfer molding operations• Can release small amounts of ammonia, formaldehyde, and phenol

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Section VI: _Phenolics, Nylon 6, & PMMS

• Thermal degradation of Phenolics• Major uses in adhesive applications (plywood & particleboard)• Compression and transfer molding operations• Can release small amounts of ammonia, formaldehyde, and phenol

– Phenol: TLV of 5 ppm, LD-50 of 414mg/kg, and LC-50 of 821 ppm.– Formaldehyde: ceiling of 0.3 ppm

• Thermal degradation of Nylon 6• Degrades into monomer_ e-caprolactam, and residual caprolactam

– Caprolactam vapor: TLV is 5 ppm, LD-50 (rat) is 2.14 mg/kg– Molding operation release some caprolactam vapor, with more produced during purging and

extrusions

• Thermal degradation of PMMA (acrylic)_ Plexiglass• PMMA degrades into MMA (methyl methacrylate)• TLV for MMA is 100 ppm (410 mg/m3)

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Section VII: Spill or Leak Procedure• Pelletized materials are swept up.• Liquid chemicals use absorbent materials• For isocyanates the absorbent materials need to allow

reaction of the isocyanate with the water in the air. The reacted materials is then disposed of according to specified government regulations.

Section VIII: Occupational Protective Measures

• Workplace protection– Adequate ventilation– Personal protective devices include

• safety glasses or goggles for eye and face protection• gloves, long sleeves, face shields, ear plugs• respirators

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Section IX: Special Precautions

• Handling • Storage

Section X: Transportation• Special instructions for transporting liquid

chemicals• Most pelletized plastics have no special

restrictions