Biodegradation of Plastics by fjwuxn

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       Lecture Week 5

Biodegradation of Plastics

 By Puan Norhayati Abdullah
Biodegradation of Plastics
 Synthetic polymers can be classified as
  plastics, elastomers and synthetic fibers.

 Plastics is the general term for a wide range of
  synthetic or semi synthetic polymerization
  products. They are composed of organic
  condensation or addition polymers and may
  contain other substances to improve
  performance or reduce costs.
 Plumbing, textiles, paint, floor coverings at
  home are mostly made of synthetic
  polymers, some of which are described as

 The term „polymer‟ are derived from Greek
  words meaning “many parts”.

 Polymers are macromolecules built up
  from linked smaller molecules called
 Benefits of using plastics:

Low cost
Strength (physically strong): lightweight
 and do not break like glass
Plastic Uses
         PLASTIC                         USES
                             Packaging, electrical
                             Credit cards, floor coverings,
Polyvinyl chloride (PVC)
Polyvinyl acetate (PVA)      Latex paints

Polybutadine (BUNA)
                             Car tires, hoses

Poly (methyl methacrylate)   Transport equipment
The Problem
 Public concern about the long term
  effects of plastics technology.

 Barry Commoner in late 1960s
  suggested that the earth surface would
  be buried ten feet deep in plastic waste
  because there were no biological
  organisms capable of destroying it.
 Plastics are the most common man-made object
  sighted at sea. During a 1998 survey, 89% of the
  trash observed floating in the North Pacific Ocean
  was plastic.

 Plastic sheeting has been documented in the
  stomachs of sperm whales, round-toothed
  dolphins and a Curvier beaked whale.

 Many sea turtles frequently swallow plastic bags
  when they mistake them for jelly fish, which is
  one of their favorite foods.
 The lightweight nature of plastics which can make
  them deadly in the marine environment, as plastic
  items can float on the surface of the ocean or
  within the water column.

 Plastics are composed of long chains of
  hydrocarbons, which are hydrogen and carbon
  atoms that are bound together very tightly. Micro-
  organisms such as plankton do not have the
  ability to break down these bonds and therefore
  plastic does not decompose easily.
 Biodegradation (Biotic degradation) -
  Chemical degradation from the action of
  naturally occurring microorganism such as
  bacteria, fungi and algae.
 A degradable plastic in which the degradation results
  from the action of naturally occurring
  microorganisms such as bacterial, fungi, and algae.
Biodegradation of Plastics
 Biodegradation of polymers involves
  breakdown by microorganisms or higher
  organisms, using enzyme-catalyzed

 Biological systems tend to degrade natural
  polymers e.g. starch by hydrolysis then
 Aliphatic e.g. nonaromatic polyesters are among
  most biodegradable.

 Example, the degradable and absorbable sutures
  used in surgical procedures are often made of
  poly (glycolic acid).

 Thermoplastic materials made from
  polycaprolactone have been shown to almost
  completely degrade on burial in soil for 12
  months. Microorganisms used the polymer as a
  growth substance and converting it into microbial
  biomass, CO2 and H2O.
 Polyethylene, polypropylene, polyvinyl chloride
  and polystyrene are most widely used plastics.

 These polymers are very bioresistant because it
  involves only carbon atoms in their main chain,
  with no hydrolyzable functional group.

 These compounds are degraded by
  microorganisms such as fungi up until the alkane
  molecular weight reaches 500. For larger alkanes,
  biodegradation becomes effectively zero.

 Chain branching inhibits biodegradation (a
  phenomenon observed with surfactants).
Influence of chain length and extent of branching
of alkanes on biodegradation by fungi mixture

                           MOLECULAR        RELATIVE
         COMPOUND                      BIODEGRADABILITY
                            WEIGHT       (0=poor, 4=good)
Hexadecane (C16H34)           226              4
Octadecane (C18H38)           255              4
Hexatriacontane (C36H74)      507              0
Tetracontane (C40H82)         563              0
                              212              0

a   Branched chain
 Materials with low molecular weights with a
  higher proportion of chain 535 carbons and
  less branching would be susceptible to

 Most biodegradable plastics are technically
  unsuitable for uses such as packaging and
  thus cannot be readily substituted for the
  less biodegradable substances.
 Biodegradation capacity can be improved
    Mixing with natural biodegradable
     substances such as starch and proteins
     e.g. conversion of cellulose into
     cellulose nitrate and cellulose acetate;
      Cellulose nitrate has been used for movie films
       and old films using this material are often in
       degraded state
 Incorporating hydrolyzable functional
  groups such as esters, amides and

 Ensuring that the main chain is flexible
  and thus able to facilitate binding to
  active sites of enzyme.
Examples of Standard Testing
for Polymer Biodegradability in Various
 ASTM D5338: Standard Test Method for
  Determining the Aerobic Biodegradation of
  Plastic Materials Under Controlled
  Composting Conditions.

 ASTM D5210: Standard Test Method for
  Determining the Anaerobic Biodegradation of
  Plastic Materials in the Presence of Municipal
  Sewage Sludge.
 ASTM D5526: Standard Test Method for
  Determining Anaerobic Biodegradation of
  Plastic Materials under Accelerated
  Landfill Conditions.

 ASTM D5437: Standard Practice for
  Weathering of Plastics under Marine
  Floating Exposure.
Logo and Certification Systems
Compostable Plastic
 A plastic that undergoes degradation by
  biological processes during composting to
  yield CO2, H2O, inorganic compounds and
  biomass at a rate consistent with other
  known compostable materials (cellulose)
  and leaves no visually distinguishable or
  toxic residues.
 Composting is an effort of developing biodegradable
  plastics for waste management and agricultural
Test and Standard for
Biodegradable/Compostable Plastics

 DIN V 54900, EN 13432 or ASTM D6400
 These standards are different in details but
  have the same basic 4 parts:
1. Material Characterization
2. Determination of Ultimate biodegradability
3. Determination of compostability
4. Analysis of the quality of the compost
1. Material Characterization
   Chemical composition, volatile solids, dry solids,
    carbon content, heavy metals in the test sample.

2. Determination of Ultimate biodegradability
   The percentage of biodegradability is obtained by
    determining the percentage of CPlastic that is
    converted to CO2 during the test.
3. Determination of compostability
    (disintegration) in pilot/full scale composting test
    The test sample must physically fall apart and
     disintegrate into invisible particles.
4. Compost quality
Testing laboratory for Polymer

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