A PROCESS FOR PREPARING POLYLACTIC ACID AND BIO PLASTICS
FROM MANGO KERNEL
FIELD OF INVENTION
[0001] The present invention relates to the field of biodegradable plastics.
Particularly  the present invention relates to the production of biodegradable plastics from
the agricultural waste  more particularly the invention is directed to a novel process for
the preparation of polylactic acid from the agricultural waste such as mango kernel 
thereby producing the biodegradable plastics.
BACKGROUND OF THE INVENTION
[0002] In recent years  there has been continuous research on improving utilization
of renewable resources and to reduce the pollution in environment. The non-renewable
resources for example fossil fuel such as coal  petroleum and natural gases are basically
the natural resources which can’t be reproduced or regenerated at its rate of consumption.
As the natural resources are getting depleted rapidly  proper utilization of the renewable
resources becomes the need of the day to combat the depletion of natural resources. Some
of the natural renewable resources such as fresh water  timber  biomass and agricultural
feed stock needs to be managed carefully to avoid exceeding the world’s capacity to
replenish them  unlike the renewable resources such as wind  solar  geothermal are
practically infinite and cannot be depleted.
[0003] From the non-renewable petroleum source  currently many products are
being manufactured/produced for example tires  synthetic rubber  shoe polish  plastics
etc. Each year  an estimated 500 billion to 1 trillion plastic bags are consumed
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worldwide. The petroleum based plastics not only reduces the natural resources but also
brings host of issues such as toxic waste in environment during the production of plastic;
highly toxic to all known living creatures from the micro-plastics. Environmental
concerns are also another reason for a global effort of reducing plastic production. Plastic
production releases toxic pollutants  green house gases and creates litter. Also  it has been
estimated that petroleum based plastics takes around 5000 years to degrade. Burning of
plastic releases toxic fumes whereas manufacturing of plastic creates chemical pollutants.
Moreover  though all these years plastics were cheaply available  recent concerns on
limited oil resources will definitely make plastic more expensive.
[0004] The rapid rate of urbanization in India has led to increasing plastic waste
generation. This increase has resulted in a large amount of plastic waste  particularly
plastic bags and PET bottles  being littered on the landscape of India.
[0005] India is the second most populous country  which has about 16% of the
world population and 25% of the land area. Rapid industrialization and urbanization in
last few decades have led to the depletion and pollution of precious natural resources in
India continuously. Therefore  rational and sustainable utilization of natural resources
and its protection from toxic releases is vital for sustainable socio-economic development
[0006] In this context  research has been carried out to contribute to the
development of efficient policy approaches on plastic waste in India. To overcome the
problems associated with the petroleum based plastics  research has been focused towards
producing a new breed of plastics from plants called bioplastics which are biodegradable 
thereby offering a solution to one of the big problems created by plastic toxic waste.
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[0007] The bioplastics or organic plastics are a form of plastics originated from
renewable biomass resources  such as corn  wheat  sweet potato  vegetable oil 
sugarcanes  pea starch  and other food products rather than fossil-fuel plastics which are
derived from petroleum. The biodegradable plastics may be composed of either
bioplastics  or petroleum-based plastics which utilize an additive. Conventionally  the
bioplastics are being manufactured by using starch based plastics  polylactic acid (PLA) 
poly-3-hydroxybutyrate (PHB)  polyamide 11 (PA 11)  bio-derived polyethylene and
genetically modified bioplastics.
[0008] The polylactic acid or polylactide (PLA) is biodegradable  thermoplastic 
aliphatic polyester obtained from renewable resources  such as corn starch  wheat  sweet
potato or sugarcanes. Polylactic acid not only resembles conventional petroleum based
plastics in its characteristics  but it can also be processed easily on standard equipment
that already exists for the production of conventional plastics. PLA is an environmental
friendly raw material substitute for traditional petroleum derived plastic
products. Although PLA has been known for more than a century  it has only been of
commercial interest in recent years  in light of its biodegradability.
[0009] Traditionally  polylactic acid is produced from the lactic acid  which is
derived from the agricultural feed stocks like corn  sweet potato  wheat and other food
source. The use of agricultural feed stocks for producing polylactic acid may result in
steep increase in food prices in the present scenario where affording food for the existing
population itself is a big challenge. Therefore  use of food source to produce PLA puts
considerable pressure to the already food deprived world. Hence  use of food source to
produce PLA is a debatable issue where the world is already facing scarcity of food.
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[00010] In light of the foregoing discussion  there is a need to provide a process that
allows to produce polylactic acid not only to overcome the above drawback associated
with the existing production of polylatic acid but also does not use agricultural feedstock
as the source  and produces PLA from non-edible agricultural wastes. Further there is a
need to have biodegradable plastics which supports sustainable agriculture.
OBJECT OF THE INVENTION
[00011] An object of the present invention is to provide a process for the preparation
of polylactic acid from agricultural waste.
[00012] Another object of the present invention is to provide a process for the
preparation of polylactic acid from the agricultural waste which includes mango kernel.
[00013] Still another object of the present invention is to address the plastic pollution
by providing an alternative to non-degradable plastics.
[00014] Yet another object of the present invention is to provide bio-degradable
plastics from agricultural waste which in turn would reduce the plastic production from
non-renewable resources like petroleum.
[00015] Another object of the present invention is to provide bio-degradable plastics
that will degrade into soil under compost condition and while degrading  would enrich
soil fertility.
[00016] Another object of the present invention is to provide a process for the
preparation of bio-degradable plastics from the agricultural waste.
[00017] Yet another object of the present invention is to provide a process for the
preparation of bio-degradable plastics from the mango kernel.
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[00018] The other objects and advantages of the present invention will be apparent
from the following description when read in conjunction with the which are incorporated
for illustration of preferred embodiments of the present invention and are not intended to
limit the scope thereof.
SUMMARY OF THE INVENTION
[00019] In view of the foregoing  an embodiment herein provides a process of
producing polylactic acid from agricultural waste  wherein the produced polylactic acid is
used for producing bio-degradable plastics.
[00020] According to an embodiment of the present invention  a process of
producing polylactic acid from mango kernel is described. In an embodiment  bacterial
fermentation is used to produce lactic acid from mango kernel. Accordingly  the process
for producing polylactic acid using mango kernel includes the step of hydrolyzing the
kernels using dilute acids at a predetermined duration and temperature to obtain the main
fermentable sugars. Further  the fermentable sugars are converted to lactic acid with the
supplement of Lactobacillus sp. The sodium lactate from the fermentation broth is
recovered by the membrane coupled electro dialysis and thereafter the lactic acid is
concentrated using a falling film evaporator. The purified and concentrated lactic acid is
used for the synthesis of the polylactic acid with the aid of the catalysis reaction with
Stannous Octate.
[00021] These and other aspects of the embodiments herein will be better
appreciated and understood when considered in conjunction with the following
description. It should be understood  however  that the following descriptions  while
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indicating preferred embodiments and numerous specific details thereof  are given by
way of illustration and not of limitation. Many changes and modifications may be made
within the scope of the embodiments herein without departing from the spirit thereof  and
the embodiments herein include all such modifications.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS
[00022] The embodiments herein and the various features and advantageous details
thereof are explained more fully with reference to the non-limiting embodiments and
detailed in the following description. Descriptions of well-known components and
processing techniques are omitted so as to not unnecessarily obscure the embodiments
herein. The examples used herein are intended merely to facilitate an understanding of
ways in which the embodiments herein may be practiced and to further enable those of
skill in the art to practice the embodiments herein. Accordingly  the examples should not
be construed as limiting the scope of the embodiments herein.
[00023] As mentioned hereinbefore  there is a need to provide a process that
produces polylactic acid from non-edible agricultural wastes. Accordingly  this invention
is directed to a process for the preparation of polylactic acid from the agricultural waste
particularly mango kernel which are not fit for human consumption. More particularly 
the disclosure is directed to a process for the preparation of lactic acid from the mango
kernel  and preparing the polylatic acid from the lactic acid. Said prepared polylactic acid
is used for the production of biodegradable plastics.
[00024] It is to be noted that even though the description of the invention has been
explained using mango kernel  it should  in no manner  be construed to limit the scope of
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the invention. The process of the invention can apply to any agricultural wastes including
tamarind see  cashew mango and other agricultural wastes.
[00025] In an embodiment  a process for the preparation of polylatic acid from the
mango kernel is described.
[00026] According to an embodiment  bacterial fermentation is used to produce
lactic acid from mango kernel  an agricultural waste. It has been observed that the lactic
acid cannot be directly polymerized to a useful product  because each polymerization
reaction generates one molecule of water  the presence of which degrades the forming
polymer chain to the point that only very low molecular weights are observed. Therefore 
according to an embodiment  the lactic acid is dimerized to make the cyclic lactide
monomer and then catalytically oligomerized to synthesize long chain lactic acid
polymer. Although dimerization also generates water  it can be separated prior to
polymerization. Further  polylactic acid [referred herein PLA] of high molecular weight
is produced from the produced lactide monomer by ring-opening polymerization using
stannous catalyst  according to an embodiment.
[00027] According to an embodiment  the process for producing polylactic acid
using mango kernel includes the step of hydrolyzing the kernels using dilute acids at a
predetermined duration and temperature to obtain the main fermentable sugars 
converting the fermentable sugars to lactic acid with the supplement of Lactobacillus sp 
recovering the sodium lactate from the fermentation broth by the membrane coupled
electro dialysis  and concentrating the lactic acid using a falling film evaporator. In a
further embodiment  the purified and concentrated lactic acid is used for the production
of the polylactic acid with the aid of the catalysis reaction with Stannous Octate.
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[00028] EXAMPLE
[00029] Before subjecting to the process of producing lactic acid  the mango kernel
is subjected to analysis for the various constituents like moisture  starch  protein  fiber
and ash using standard procedure  and it has been observed as shown below table 1
Protein 6.76%
Fat 8.9%
Starch 68%
Sugar 1.07%
Fiber 2.17%
Sulfur 0.23%
Table 1
[00030] Thereafter  the mango kernel is dried and pulverized to form micro particle
of mango kernel in the range of 90-200 micron  wherein the pulverization can be
performed by using any known pulverizer. The powered kernel is packed in autoclavable
plastic bags and stored at room temperature. The kernel powder thus produced is then
digested using the dilute acids like HCl & H2SO4 for 3 hrs reaction time and at constant
temperature to form a solution.
[00031] Further  the hydrolyzed mango kernel powder is then neutralized with
commercial grade NaOH. Thereafter  for sterilization and filtration  the solution is
clarified with activated carbon to remove the phenolic components and other impurities.
The filtrated solution is subjected to evaporation for concentrating the solution to desired
level. Lactic acid is produced from the concentrated solution through the fermentation
process by subjecting the desired concentration of reducing sugars along with
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Lactobacillus sp and good fermentation conditions are maintained to produce the lactic
acid. Lactobacillus is a genus of rod-shaped bacteria; part of the lactic acid bacteria
group.
[00032] Fermented sodium lactate  thus produced  is purified with the membrane
coupled electro dialysis. Then the purified lactic acid is concentrated using falling film
evaporator. A falling film evaporator is an industrial device to concentrate solutions 
especially with heat sensitive components. The evaporator is a special type of heat
exchanger. Finally  the concentrated lactic acid is converted to PLA using a catalyst
Stannous Octate.
[00033] In an embodiment of the present invention  to obtain lactic acid from
agricultural waste  the agricultural feed stock like mango kernel starch is hydrolyzed
using the dilute acids at a particular temperature and with 3h reaction time to obtain the
main fermentable sugars. These fermentable sugars are converted to lactic acid with the
supplement of Lactobacillus sp. The rate of formation of lactic acid through the
fermentation process is 2.25g/L/hr. The sodium lactate from the fermentation broth is
recovered by the membrane coupled electro dialysis in a single step which is proven to be
economical and cuts down hazardous solvents. The lactic acid is concentrated using the
falling film evaporator. The purified and concentrated lactic acid is used for the synthesis
of the poly lactic acid with the aid of the catalysis reaction with Stannous Octate and the
approximate yield efficiency is 280 gm/kg of mango kernel powder.
[00034] According to the present invention  it has been observed that the conversion
efficiency of the starch to reducing sugars from the mango kernel waste is 82%. These
sugars when subjected to the fermentation process  the rate of formation of lactic acid
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were seen to be 2.25g/L/hr. By using the above mentioned process  polylactic acid of 280
gm / kg of mango kernel powder was synthesized using lactic acid. Therefore  A
kilogram of crushed mango kernel yields over 320 grams of Lactic acid which in turn
converted to 280 gms of polylactic acid  with a molecular weight of around 10000-15000.
[00035] In an embodiment  the preparation of bio-degradable plastic from the
polylactic acid can be obtained in any conventional process.
[00036] The main advantage of the present invention is that it makes use of
renewable agriculture waste which is not edible. In this way  it does not use food stocks
to create PLA; rather it uses non-edible waste  thereby assisting in waste management
and not using food resources of an already food-deprived world.
[00037] Large quantities of crop residues are produced annually worldwide  and are
vastly underutilized. India  being an agricultural country  generates considerable amounts
of renewable agricultural waste  namely mango kernel  and by proper utilization of these
waste according to the present invention can enable to produce approximately 1.5 to 2.00
million tons of bio-plastics. Accordingly  the present invention enables to produce
bioplastics which is an alternative to existing petroleum based plastics which are causing
a havoc in the modern society creating a ‘White Pollution’ and are manufactured from
depleting natural resources.
[00038] Another advantage of present invention is that utilization of such waste
material to manufacture PLA also assists in waste management and reduces pressure on
use of other crops such as corn starch  sugarcane which are at present being used to
manufacture PLA.
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[00039] Another advantage of present invention is that the product made using the
invented process is not only environment friendly  in-expensive and economical but also
makes use of agriculture waste and reduces pollution.
[00040] Yet another advantage of the present invention is that since it is made of
biodegradable resources  it degrades faster and as and when it degrades  it increases the
fertility of the soil  unlike conventional plastics which create toxins and takes thousands
of years to degrade.
[00041] The foregoing description of the specific embodiments will so fully reveal
the general nature of the embodiments herein that others can  by applying current
knowledge  readily modify and/or adapt for various applications such specific
embodiments without departing from the generic concept  and  therefore  such
adaptations and modifications should and are intended to be comprehended within the
meaning and range of equivalents of the disclosed embodiments. It is to be understood
that the phraseology or terminology employed herein is for the purpose of description and
not of limitation. Therefore  while the embodiments herein have been described in terms
of preferred embodiments  those skilled in the art will recognize that the embodiments
herein can be practiced with modification within the spirit and scope of the embodiments
as described herein.
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We Claim:
1. A process for the preparation of lactic acid from mango kernel  wherein the
process comprising the step of
hydrolyzing the mango kernels using dilute acid at a predetermined duration
and temperature to obtain the fermentable sugars;
converting the fermentable sugars to lactic acid with the supplement of
Lactobacillus sp;
recovering the sodium lactate from the fermentation broth by the membrane
coupled electro dialysis; and
concentrating the lactic acid using a falling film evaporator.
2. The process for the preparation of claim 1  wherein said dilute acid is selected
from the group comprises of HCl  H2SO4.
3. The process for the preparation of claim 1  wherein said duration is in the
range of 2 to 4 hrs.
4. The process for the preparation of claim 1  wherein the lactic acid yield
efficiency is 280 gm/kg of mango kernel powder.
5. The process for the preparation of claim 1  wherein efficiency of the starch to
reducing sugars is about 82% from the mango kernel.
6. The process for the preparation of claim 1  wherein said lactic acid is
converted to polylatic acid using a catalyst.
7. The process for the preparation of claim 6  wherein said catalyst is a stannous
Octate.
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8. The process for the preparation of claim 6  wherein said polylactic acid is used
for the preparation of bio-degradable plastics.
9. A process for the preparation of bio-degradable plastics from mango kernel 
wherein the process step comprises of
hydrolyzing the mango kernels using dilute acid at a predetermined duration
and temperature to obtain the fermentable sugars;
converting the fermentable sugars to lactic acid with the supplement of
Lactobacillus sp;
recovering the sodium lactate from the fermentation broth by the membrane
coupled electro dialysis;
concentrating the lactic acid using a falling film evaporator;
converting the concentrated lactic acid to polylactic acid using a catalyst
stannous Octate; and
preparing boi-degradable plastics from the polylactic acid using one or more
conventional process.
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