Biopolymers Flashcards
Definitions
Bio-based polymers: polymers produced (at least in part) from renewable natural resources e.g. PLA, PHA – see later
Often maize as a source material
PLA Poly-lactic acid currently has relatively high volumes and is targeted for fastest growth
Drop-in bio-based polymers: chemically identical to conventionally sourced polymers, but are (at least partially) produced from biomass e.g. PET
PET for carbonated drinks bottles and other packaging
Biodegradable: their properties deteriorate and they may completely degrade under aerobic (oxygen available, e.g. composting) or anaerobic (no oxygen, e.g. landfill) conditions
Only 25% of bio-based polymers are biodegradable; some petrochemical-based polymers are biodegradable
Starch-based polymers derived from potatoes
Biopolymers: sometimes used for bio-compatible polymers (which may or may not be bio-based) suitable for biomedical applications
Silicon rubber
Properties of Biopolymers
PLA Poly-lactic acid currently has relatively high volumes and is targeted for
fastest growth
PHA Poly-hydroxy-alkanoates. Some doubts over ability to scale-up
Starch-based blends: mixed with other polymers to produce range of
properties to substitute for PP (polypropylene), PE (polyethylene), EPS
(expanded polystyrene)
Drop In Bio Based
PET for carbonated drinks bottles and other packaging (driven initially by
Coca-Cola, but plastic bottle industry has come under intense pressure
recently).
Derived from bio-based ethanol feedstocks (sugar cane).
PE (polyethylene) and PP (polypropylene) are also gaining market share
(derived from same feedstocks).
PUR Polyurethane (thermoset). Used for coatings, biodegradable.
Biodegradable Plastics Applications
Starch-based polymers
blended with other polymers to
make materials with a range of properties
* Lower starch content associated with improved properties
BUT decreased biodegradation
* Substitute for PE, PP and EPS (Expanded Polystyrene)
* Food and agricultural applications
PLA
Physical properties similar to PS
* Can be modified to resemble PE and PP
* Grease resistance comparable to PET
* Degrades by hydrolysis
* Food and medical applications
PHA
Comparable to PP
* Can also substitute for PE and PVC
* Degrades in composting and anaerobic conditions
Food services: eating and drinking on-the-go
Good for convenience; food hygiene and safety
Potentially good for disposal in same way as food
Bad for single-use plastic usage (coming under scrutiny)
Agriculture and horticulture:
e.g. Black plastic films ‘Mulching films’ extensively used to suppress weeds, conserve water, moderate soil temperature, and stabilise soil composition. Conventional plastics are ploughed into soil and accumulate, or laboriously gathered by hand. Real advantages from using biodegradable films (degrade over 2 years)
PBAT (polybutylene adipate terephthalate) currently expensive but may have potential. Fossil fuel based plus 30% biobased content (starch, PLA)
Issues
Intensive Agriculture
Large scale monocultures so a large amount of pesticides used
Massive water requirements
Land
Production capacities
Competition with biofuels
Competition with food crops:
land use for bioplastics is negligible compared to food
Energy Requireme
Significant fossil energy is used for the production
Synthetic fertilisers: mined or often produced from natural gas
Pesticides: similarly resource intensive to manufacture but used in smaller amounts
Farm machinery
Lights, pumps, fans and heating
Water: huge water resources
Can take more energy than production from petrochemicals
Cost
More expensive than conventional polymers
Disposal
Home and industrial composting
Degraded by aerobic micro-organisms into carbon dioxide and water
Timescale: days to weeks
Anaerobic digestion
Degrade in the absence of oxygen through a series of processes ultimately resulting in carbon dioxide and methane, e.g. sewage treatment
Timescale: days to a few weeks
Landfill
Either zero or anaerobic degradation
Methane is generated if there is degradation
Timescale: weeks to years, or longer
Issues
May not degrade in natural environment
Mostly not suitable for home composting (temperatures not high enough) Will it get into the industrial composting waste stream? All plastics usually rejected, because biodegradable plastics can’t easily be distinguished from non-biodegradable plastics
And if it does get there: may not degrade sufficiently fast in industrial composters
Anaerobic digestion becoming more popular: biopolymers may not degrade
Generate methane if degradable in landfill
Life Cycle Assessment
Standardised framework for determining the environmental impact of a product or process, to allow comparisons to be made
Define System/ boundary
User defined scope
Grey areas
Soil dynamics
Nitrogen emissions from composting
Manufacturing environment
Difficulties Analysing LCAs
Location-specific
Transport requirements
Incineration efficiencies
Farming practice
Energy used (production is country-specific)
Impact categories
Contribution to climate change
Resource depletion
Ozone depletion
Energy and water use
Acidification
Eutrophication
Smog formation
Future
Technological developments:
polymer development (e.g. mechanical properties, biodegradability)
polymer manufacturing process:
improve efficiencies of existing processes ‘breakthrough’ needed for lignocellulosic feedstocks
Economics
increase in fossil fuel prices will make biopolymers financially attractive prices of feedstocks (especially fermentable sugar) need to reduce
Feedstock production
Optimisation of current sources:
More use of renewable energy
Improved farming practices
‘Integrated farming’ – best practice across all operations
Reduction in agrichemicals
Reduction in fuel costs
Alternative feedstocks:
Non-food crops; waste?
Biopolymers from Waste
Agricultural waste: already used by some
Expanding to other crops and improving process efficiencies
Other waste such as food: problems of contamination
Waste water from some industrial processes looking viable
