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Life cycle Assesment and waste stratigies of PLA
1. SEMINAR PRESENTATION
Group 2
R Rashid Iqbal (16-ARID-2565)
Ejaz ul Haq (16-ARID-2543)
Sabahat Ali (16-Arid-2569)R
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2. POLYLACTIC ACID WASTE STRATIGIES
Contents
• Production
• Recycling
• Biodegradation of Polylactic Acid
• Impacts of Polylactic Acid
3. INTRODUCTION
• Polylactic acid or polylactide (PLA) is
a thermoplastic aliphatic polyester derived from renewable resources.
• In 2010, PLA had the second highest consumption volume of
any bioplastic of the world, although it is still not a commodity polymer.
• Its widespread application has been hindered by numerous physical and
processing shortcomings.
• The name "polylactic acid" does not comply with IUPAC standard
nomenclature, and is potentially ambiguous or confusing, because PLA is
not a polyacid (polyelectrolyte), but rather a polyester.
4. PRODUCTION
There are three routes for synthesis of PLA.
(1) Polymerization (2) Condensation (3) Fermentation
Polymerization
• The monomer is typically from fermented plant starch such as
from corn, cassava, sugarcane or sugar beet pulp.
• Several industrial routes afford usable (i.e. high molecular weight) PLA. Two main
monomers are used: lactic acid, and the cyclic di-ester, lactide.
• The most common route to PLA is the ring-opening polymerization of lactide with
various metal catalysts (typically tin octoate) in solution or as a suspension.
• The metal-catalyzed reaction tends to cause racemization of the PLA, reducing its
stereoregularity compared to the starting material (usually corn starch).
5. Condensation
• Another route to PLA is the direct condensation of lactic acid monomers.
This process needs to be carried out at less than 200 °C; above that
temperature, the entropically favoured lactide monomer is generated.
• This reaction generates one equivalent of water for every condensation
(esterification) step. The condensation reaction is reversible and subject to
equilibrium, so removal of water is required to generate high molecular
weight species.
• Water removal by application of a vacuum or by azeotropic distillation is
required to drive the reaction toward polycondensation. Molecular weights
of 130 kDa can be obtained this way.
• Even higher molecular weights can be attained by carefully crystallizing
the crude polymer from the melt.
6. • Carboxylic acid and alcohol end groups are thus concentrated in the
amorphous region of the solid polymer, and so they can react.
Molecular weights of 128–152 kDa are obtainable thus.
Polylactic Acid
7. Fermentation
• Lactic acid (2-hydroxy propionic acid), the single monomer of PLA, is
produced via fermentation or chemical synthesis.
• Its 2 optically active configurations, the L(+) and D(−) stereoisomers are
produced by bacterial (homofermentative and heterofermentative)
fermentation of carbohydrates
• Industrial lactic acid productionutilizes the lactic fermentation process rather
than synthesis because the synthetic routes have many major limitations,
including limited capacity due to the dependency on a by-product of another
process, inability to only make the desirable L-lactic acid stereoisomer, and
high manufacturing costs.
8.
9. CHEMICAL RECYCLING OF PLA
There are many processes available for chemical recycling of PLA but most
commonly used method which is given below:
• Hydrolytic or alcoholytic depolymerisation
OR
• The Zeus Waste PLA Depolymerization Process
However, these processes are inclined to be high-temperature, energy-intensive
ones. In recent times, processes utilizing temperatures as low as 80 °C have been
disclosed , thus enhancing the economics of chemical recycling.
11. The Zeus Waste PLA Depolymerization
Process:
• The Zeus process further improves the economic feasibility of PLA
depolymerization processes by using miscible systems of
PLA/solvent/reactant to enable monomer recovery at even lower
temperatures in a very efficient, environmentally-friendly manner.
• Following figure illustrates one possible configuration of unit operations
in a depolymerization process to handle a stream of commingled plastic
post-consumer waste that includes scrap PLA according to the Zeus
process.
13. Process:
• After a preliminary washing step, the commingled plastic stream is subjected
to size reduction using standard techniques such as grinders and shredders to
make flake-size granules that can be easily separated.
• Separation of the different plastics can be done in a range of ways including
infrared techniques, electrostatic separation, as well as flotation.
• The vital part of the process is dividing biodegradable plastics like PLA from
reprocessable plastics like PET.
• In a mixed stream of polyesters, this splitting-up can be performed by
contacting the stream with a solvent like chloroform to dissolve the PLA
component.
14. Continued…….
• The undissolved PET can then be dried and sent for additional processing.
• The PLA solution is then exposed to alcoholysis (reaction with an alcohol).
High molecular weight PLA can be dissolved to around 15% by weight into
chloroform.
• Alcohol is then included in stoichiometric excess to suit depolymerization. As
long as the PLA stays dissolved, the scission reactions can take place
without being restricted by interphase transport of the reactant to the
polymer.
• Temperature can be raised to just below the boiling point of the mixture’s
lowest boiling component to accelerate the reaction without requiring high-
pressure equipment.
15. Continued…….
• The incorporation of a tin catalyst has been found to significantly increase the
reaction kinetics at these mild conditions of temperature.
• Since the depolymerization process takes place at low temperatures and
atmospheric pressures, a range of reactors can be used.
• Plug flow reactors or continuous stirred tank reactors are instances of the more
common types.
• Stirred tank reactors can be employed in series to make the process more
efficient by increasing the concentration of alcohol in subsequent vessels to
favourably drive the reaction to monomer while maintaining solubility of the
oligomers.
• Separation of the alcohol and solvent from the resultant monomers is also
readily achieved.
16. Continued…….
• For the chloroform/methanol/methyl lactate system, the variances in boiling
points of the components (61 °C for chloroform, 65 °C for methanol and 154
°C for methyl lactate) make distillation an ideal suitable process to eliminate
the reactant and solvent from the product.
• The same is true of the THF/water/lactic acid system (66 °C for THF, 100 °C
for water and 122 °C for lactic acid).
• In each case, the solvent can be recondensed and returned to the contacting
tank, while the unreacted methanol or water can be blended with fresh
reactant and sent back to the reactor vessel.
• Solubility of the PLA in THF or methanol can be significantly improved by
heating up the mixture to just below the boiling points of the respective
solvents.
• The respective reactants are then incorporated into the PLA solution at
reaction temperature.
17. Continued…….
• In experiments performed at just below 60 °C and atmospheric pressure,
molecular weight reduction of the PLA was obvious in each solution within a
few hours.
• Depolymerization extent was deduced by measuring innate viscosity at varied
reaction conditions. Size exclusion chromatography was used to establish
changes in molecular weight distribution for designated reaction conditions.
• It was discovered that polydispersity remains fairly unchanged as the reaction
continues, signifying that random chain scission is the main mechanism in the
single-phase systems .
• The presence of substantial amounts of methyl lactate monomer was
established for the case of the PLA/chloroform/ methanol system using gas
chromatography.
• The ensuing monomer, either lactic acid or methyl lactate, can be used to
synthesize PLA again.
18. Continued…….
• There are a number of proven routes to transforming these monomers into
PLA, including azeotropic dehydrative polycondensation, polycondensation, or
a multistep route that results in high molecular weight PLA .
• The multistep process polymerizes the monomer into low molecular weight
PLA, also known as a pre-polymer, that is then depolymerized to produce
lactide.
• The methyl lactate is not required to be converted into lactic acid before the
pre-polymerization step.
• The lactide experiences ring-opening polymerization, typically in the presence
of a tin catalyst, to produce a high molecular weight PLA resin. Alternately, the
pre-polymer can be joined together using chain extending agents to yield a
higher molecular weight PLA .
• The preferred reaction route relies on the PLA characteristics required in the
end use application. The reintroduction of monomers back into the PLA life
cycle concludes the life cycle.
19. POLYMER SOLVENT REACTANT CATALYST MONOMER
PLA
chlorofor
m
methanol
tin(II)
octanoate
methyl
lactate
PLA THF water
tin(II)
octanoate
lactic acid
Examples of Suitable Systems for PLA Depolymerization Process
Conclusion
The process is versatile. Both commercial and medical grade
PLA resins can be depolymerized.
Benefits of the Zeus Depolymerization Process
Key Benefits
•Cost-effective
•Easy to implement
•Supports sustainability
20. BIODEGRADATION OF PLA
PLA is degraded abiotically by three mechanisms:[
1. Hydrolysis: The ester groups of the main chain are cleaved, thus reducing
molecular weight.
2. Thermal degradation: A complex phenomenon leading to the appearance
of different compounds such as lighter molecules and linear and cyclic
oligomers with different Mw, and lactide.
3. Photodegradation: UV radiation induces degradation. This is a factor
mainly where PLA is exposed to sunlight in its applications in plasticulture,
packaging containers and films.
21. The hydrolytic reaction is:
COO + H₂O COOH + OH‾
• The degradation rate is very slow in ambient temperature.
• Pure PLA foams are selectively hydrolysed in Dulbecco's modified Eagle's
medium (DMEM) supplemented with fetal bovine serum (FBS) (a solution mimicking body
fluid).
• After 30 days of submersion in DMEM+FBS, a PLLA scaffold lost about 20% of its weight.
• PLA samples of various molecular weights were degraded into methyl lactate (a green
solvent) by using a metal complex catalyst.
• PLA also be degraded by some bacteria, such as Amycolatopsis and Saccharothrix. A
purified protease from Amycolatopsis sp., PLA depolymerase, can also degrade PLA.
Enzymes such as pronase and most effectively proteinase K from Tritirachium
album degrade PLA.
22. Four possible end of life scenarios are the most common:
1. Recycling: which can be either chemical or mechanical. Currently, the SPI resin
identification code is applicable for PLA. In Belgium, Galactic started the first pilot
unit to chemically recycle PLA . Unlike mechanical recycling, waste material can
hold various contaminants. Polylactic acid can be recycled to monomer by thermal
depolymerization or hydrolysis. When purified, the monomer can be used for the
manufacturing of virgin PLA with no loss of original properties (cradle-to-cradle
recycling).
2. Composting: PLA is biodegradable under industrial composting conditions,
starting with chemical hydrolysis process, followed by the microbial digestion, to
ultimately degrade the PLA.
3. Incineration: PLA can be incinerated, leaving no residue and producing 19.5
MJ/kg of energy.
4. Landfill: the least preferable option is landfilling because PLA degrades very
slowly in ambient temperatures.
23. IMPACTS OF POLYLACTIC ACID
POSITIVE IMPACTS:
• Eco-friendliness:
PLA is produced from renewable sources(corn,wheat,rice).In
addition it is biodegradable,recycleable and Compostable.Its production consumes.
Carbon Dioxide.
• Biocompatibility:
Main PLA degradation product,lactic acid is non toxic and
metabolized by the organism itself.
• Processability:
PLA has a better thermal processability than other biopolymers.
it can be processed through injection molding,film extrusion,blow molding,
thermoforming,fiberspinning and filmforming.
24. • Energy saving:
PLA requires 25%_55% less energy than petroleum based polymers.
• Time saving:
There is no need for the time consuming logic design of random logic
gate network and even more time consuming layout.
• Easy Design:
Design Checking is easy and design change is also easy.
Only the connection mask needs to be custom made.
• Simple Layout:
Layout is far simpler than that for random logic gate networks
and is far less time consuming.
26. Mulch film made of PLA-blend "bio-flex" 3D printed human skull with data
from computed tomography.
Transparent PLA.
27. NEGATIVE IMPACTS:
• Poor toughness:
PLA is very brittle material,whose elongation at break is
less than 10%.This can represent a limit for those applications that need
plastic deformation at high stress levels.
• Slow Degradation Rate:
PLA naturally degrades through hydrolysis, whose rate
depends on many factors, such as crystallinity and molecular weight.Slow
PLA degradation leads to high life time of devices in vivo,and can raise issues
for disposal of commodities.
• Hydrophobicity:
PLA is relatively hydrophobic material(static water contact
angle value is about 80 degree).This result in low cell affinity and can lead
to inflammatory response upon direct contact to biological fluids.
28. • Lack of side chain Groups:
PLA is chemically inert which makes surface
functionalization and bulk modification challenging tasks.
• Tedious and Time Consuming:
Random logic gate networks occupy smaller
chip areas than PLAs or ROMs,although the logic design and the layout off
random logic gate networks are far more tedious and time consuming.
• Cheaper:
Also with large production volumes,random logic gate
networks are cheaper than PLAs or ROMs.
• Random logic gate networks have higher speed than PLAs or ROMs
