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AL Chemistry Group Project ( TAS )AL Chemistry Group Project ( TAS )AL Chemistry Group Project ( TAS )AL Chemistry Group Project ( TAS )

Group Member: 1. Chan Ka Long (3) 2. Cheng Chun Shing (7) Class: 6S

Topic : Green Chemistry

We have chosen the manufacture of polylactic acid (PLA) polylactic acid (PLA) polylactic acid (PLA) polylactic acid (PLA) as our project

target.

PLA is one of the most biodegradable polymer in the world. It has been

used in different areas because it is cheap and has many remarkable properties

and its properties are also related to the principle of green chemistry.

(I) It is better to prevent waste than to treat or clean up waste after it is formed.

The raw material of PLA is lactic acid which can be obtained by the

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bacterial fermentation of starch in corn. By-products of the conversion from

carbohydrates to lactic acid are acetic acid,ethanol, glycerol, carbon dioxide,

etc, and they will not cause any permanent damage to our environment when

we deal with them. Also, during the polymerization of PLA, water is the main

by-product and can be removed easily.

(II) Synthetic methods should be designed to maximize the incorporation of all materials

used in the process into the final product.

Although by-products are produced is the conversion from

carbohydrates to lactic acid, they can be eliminated by using the

homo-fermentative method. It leads to greater yield of lactic acid and smaller

amount of by-products. The percentage of yield from glucose to lactic acid is

more than 90%.

(III)Wherever practicable, synthetic methodologies should be designed to use and generate

substances that possess little or no toxicity to human health and the environment.

The raw material of PLA is corn which is non-toxic. The processes and

the products are not harmful

to our environment and body. That's why PLA is commonly used in food

packaging and operation

tools.

(IV)Chemical products should be designed to preserve efficacy of function while reducing

toxicity.

PLA can be used in different areas already and it is non-toxic. However,

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one of its disadvantages is that its melting point is low, only about 60 degree

Celsius. If PLA is processed into fiber, its melting point can increase about

40-50 degree Celsius. The disadvantage of this fiber is that it will take a

relatively longer time to be decomposed but it will not pollute the

environment.When added with aluminum hydroxide,it will become a flame

retardant auxiliary agent.

(V)The use of auxiliary substances (e.g. solvents, separation agents, etc.) should be made

unnecessary wherever possible and innocuous when used.

The Nature Works company discovered a method which doesn't require

the use of hazardous organic solvents typical in other PLA processes. PLA

produced by this method still is in a highquality and recyclable.

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(VI)Energy requirements should be recognized for their environmental and economic

impacts and should be minimized. Synthetic methods should be conducted at ambient

temperature and pressure.

The bacterial fermentation and the polymerization does not require very

high temperature and pressure. Less energy is required.

(VII)A raw material or feedstock should be renewable rather than depleting wherever

technically and economically practicable.

PLA is made from renewable resources, such as corn, tapioca and

sugarcanes. Compared with a similar fiber PET which is made from

petroleum, the raw materials of PLA can be restored periodically. 20% - 50%

fewer fosil resources used than with petroleum based resins.

(VIII)Reduce derivatives - Unnecessary derivatization (blocking group, protection/

deprotection,temporary modification) should be avoided whenever possible.

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One of the derivatives in the polymerization is the PLA with low

molecular mass. The main reason resulting in low molecular mass PLA

because PLA is made directly by condensation polymerization from lactic

acid. In order to reduce derivatives, PLA can be obtained by Azeotropic

dehydration condensation or ring-opening polymerization, PLA obtained by

these methods will have relatively high molecular mass.

(IX)Catalytic reagents (as selective as possible) are superior to stoichiometric reagents.

Lactobacilli is a kind of bacteria using in the fermentation, it acts as a

catalyst to speed up the conversion from starch to lactic acid. A stannous

octoate catalyst is used in the polymerization in order to get PLA with high

molecular mass. Tin(II) chloride is used as a catalyst instead of octoate

in laboratory.

(X)Chemical products should be designed so that at the end of their function they do not

persist in

the environment and break down into innocuous degradation products.

PLA is a biodegradable substances. We only need hot water to degrade

them and no toxin will released. Also, only water and carbon dioxide will be

produced if it is degraded under certain temperature and pressure.

(XI)Analytical methodologies need to be further developed to allow for real-time,

in-process monitoring and control prior to the formation of hazardous substances.

In 2002, Cargill Dow improved PLA polymerization process. Futerro,a

PLA manufacture company is developing a second generation of polylactic

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acid product. It was monitored for a period of time to ensure that it is safe and

stable.And now it does not have any problem.

(XII)Substance and the form of a substance used in a chemical process should be chosen so

as to minimize the potential for chemical accidents, including releases, explosions,

and fires.

The polymerization of PLA requires only low temperature and pressure

condition so that it has less potential hazards e.g. overheating,explosions,fire

accident.etc