BIO-RESOURCE , PAPER & COATINGS

SCHOOL OF INDUSTRIAL TECHNOLOGY

UNIVERSITI SAINS MALAYSIA

ASSIGNMENT IWK 305/2

TITLE : BIODEGRADABLE & ENVIRONMENTAL FRIENDLY STARCH

NAME : FARID AIMAN BIN NASIR

MATRIX NO. : 107970

LECTURER : DR. TAY GUAN SENG

Biodegradable

Biodegradation is the chemical dissolution of materials by bacteria or other biological means.

Although often conflated, biodegradable is distinct in meaning from compostable. While

biodegradable simply means to be consumed by microorganisms and return to compounds

found in nature, "compostable" makes the specific demand that the object break down in a

compost pile.

The term is often used in relation to ecology, waste management, biomedicine, and the natural

environment (bioremediation) and is now commonly associated with environmentally friendly

products that are capable of decomposing back into natural elements. Organic material can be

degraded aerobically with oxygen, or anaerobically, without oxygen. Biosurfactant, an

extracellular surfactant secreted by microorganisms, enhances the biodegradation process.

Biodegradable matter is generally organic material such as plant and animal matter and other

substances originating from living organisms, or artificial materials that are similar enough to

plant and animal matter to be put to use by microorganisms. Some microorganisms have a

naturally occurring, microbial catabolic diversity to degrade, transform or accumulate a huge

range of compounds including hydrocarbons (e.g. oil), polychlorinated biphenyls (PCBs),

polyaromatic hydrocarbons (PAHs), pharmaceutical substances, radionuclides, pesticides and

metals.

Major methodological breakthroughs in microbial biodegradation have enabled detailed

genomic, metagenomic, proteomic, bioinformatic and other high-throughput analyses of

environmentally relevant microorganisms providing unprecedented insights into key

biodegradative pathways and the ability of microorganisms to adapt to changing environmental

conditions. Products that contain biodegradable matter and non-biodegradable matter are often

marketed as biodegradable.

Starch

Starch or amylum is a carbohydrate consisting of a large number

of glucose units joined by glycosidic bonds. This polysaccharide is produced

by all green plants as an energy store. It is the most common carbohydrate in

the human diet and is contained in large amounts in such staple

foods as potatoes, wheat, maize (corn), rice, and cassava.

Pure starch is a white, tasteless and odorless powder that is insoluble in cold water or alcohol. It

consists of two types of molecules: the linear and helical amylose and the

branched amylopectin. Depending on the plant,

starch generally contains 20 to 25% amylose and

75 to 80% amylopectin by weight. Glycogen, the

glucose store of animals, is a more branched

version of amylopectin.

Starch is processed to produce many of the sugars

in processed foods. Dissolving starch in warm water

gives wheat paste, which can be used as a

thickening, stiffening or gluing agent. The biggest

industrial non-food use of starch is as adhesive in

the papermaking process. Starch can be applied to

parts of some garments before ironing, to stiffen

them; this is less usual now than in the past.

To most people, starch is viewed as a major

nutritional material to provide energy for human

or as a major functional ingredient in food recipes to provide characteristic viscosity,

texture, mouth-feel and consistency of many food products. However, in fact, starch has

found uses in various nonfood applications such as paper, textile, cosmetic and

pharmaceutical industries.

The Properties of Starch

Structure

While amylose was traditionally thought to be completely unbranched, it is now known that

some of its molecules contain a few branch points. Although in absolute mass only about one

quarter of the starch granules in plants consist of amylose, there are about 150 times more

amylose molecules than amylopectin

molecules. Amylose is a much smaller

molecule than amylopectin.

Starch becomes soluble in water when heated.

The granules swell and burst, the semi-

crystalline structure is lost and the smaller

amylose molecules start leaching out of the

granule, forming a network that holds water

and increasing the mixture's viscosity. This

process is called starch gelatinization.

Some cultivated plant varieties have pure

amylopectin starch without amylose, known

as waxy starches. The most used is waxy

maize, others are glutinous rice and waxy potato starch. Waxy starches have less retro

gradation, resulting in a more stable paste. High amylose starch, amylomaize, is cultivated for

the use of its gel strength and for use as a resistant starch (a starch that resists digestion) in

food products.

Hydrolysis

The enzymes that break down or hydrolyze starch into the constituent sugars are known

as amylases. Alpha-amylases are found in plants and in animals. Human saliva is rich in

amylase, and the pancreas also secretes the enzyme. Beta-amylase cuts starch

into maltose units. This process is important in the digestion of starch and is also used

in brewing, where amylase from the skin of seed grains is responsible for converting starch to

maltose.

Chemical tests

Iodine solution is used to test for starch; a dark blue color indicates the presence of starch. The

details of this reaction are not yet fully known, but it is thought that the iodine (I3− and I5

− ions) fit

inside the coils of amylose, the charge transfers between

the iodine and the starch, and the energy level spacings

in the resulting complex correspond to the absorption

spectrum in the visible light region. The strength of the

resulting blue color depends on the amount of amylose

present. Waxy starches with little or no amylose present

will color red.

Starch indicator solution consisting of water, starch and iodine is often used in redox titrations:

in the presence of an oxidizing agent the solution turns blue, in the presence of reducing

agent the blue color disappears because triiodide (I3−) ions break up into three iodide ions,

disassembling the starch-iodine complex. A 0.3% w/w solution is the standard concentration for

a starch indicator. It is made by adding 3 grams of soluble starch to 1 liter of heated water; the

solution is cooled before use (starch-iodine complex becomes unstable at temperatures above

35 °C).

Each species of plant has a unique type of starch granules in granular size, shape and

crystallization pattern. Under the microscope, starch grains stained with iodine illuminated from

behind with polarized light show a distinctive Maltese crosseffect (also known as extinction

cross and birefringence).

Production Process

The production of potato starch comprises the steps such as delivery and unloading potatoes,

cleaning, rasping of tubers, potato juice separation, starch extraction, starch milk rafination,

dewatering of refined starch milk and starch drying.

Delivery and unloading potatoes

Potatoes are delivered to the starch plants via road or rail transport. Unloading of potatoes could

be done in two ways:

1. dry - using elevators and tippers,

2. wet - using strong jet of water.

Cleaning

Coarsely cleaning of potatoes takes place during the transport of potatoes to the scrubber by

channel. In addition, before the scrubber, straw and stones separators are installed. The main

cleaning is conducted in scrubber (different kinds of high specialized machines are used). The

remaining stones, sludge and light wastes are removed at this step. Water used for washing is

then purified and recycled back into the process.

Rasping of tubers

Most often the rasping of potato tubers is carried out with a rotary with a rotary grater. The

purpose of this stage is disruption of cell walls, which therefore release the starch. In practice,

potato cells are not entirely destroyed and part of the starch remains in the mash. Potato pulp

rapidly turns dark, because tyrosine presented in the potato is oxidised by polyphenol oxidase,

which is located in the cellular juice. Therefore, cellular juice must be separated as soon as

possible.

Potato juice separation

This allows the recovery full-value protein from juice and reduces the onerousness of water

juice as a sludge.

Starch extraction

After separation of potato juice the pulp is directed to the washing starch station, to isolate the

starch. Most used are stream-oriented washers. In these machines pulp diluted with water is

washed with a strong stream of water to flush out the milk starch. The mash smuggling with

water is a waste product – dewatered potato pulp. Starch milk is contaminated by small fiber

particles (potato tissue fragments) and the remaining components of the potato juice – that’s

why it is called raw starch milk.

Starch milk raffination

Raw starch milk is purified in the refining process. This involves the removal of small fibers from

the starch milk and then the removal of juice water and starch milk condensation. For this

purpose, the screens and hydrocyclones are commonly used. Hydrocyclones due to the low

output (approximately 0.3 cubic meter per hour) are connected in parallel and works as

multihydrocyclones. For the starch milk desanding bihydrocyclones are used. In order to prevent

enzymatic darkening of potato juice the chemical refining of starch is carried out using sulfurous

acid. Refined starch milk has a density of about 22° Be, which is about 38% of starch.

Dewatering of refined starch milk and starch drying

It is a suspension of starch in water, which needs dewatering up to 20% of moisture. This is

equivalent to the moisture content of commercial starch when stored. High temperature cannot

be use in this process because of the danger of starch gelatinization which destoyes granular

structure. It may result in significant changes of the functional starch properties. Therefore,

removal of excess water from milk shall be done only under conditions that prevent the

gelatinization of starch.

Dewatering of refined starch milk is carried out in two stages. In the first stage the excess water

is removed by means of a rotary vacuum filter. Secondly moist starch is dried, without starch

pasting. For this purpose a pneumatic dryier is used. In this device moist starch (with water

content 36 – 40%) is floating in strong and hot (160°C) air flow and then dried during 2 – 3

seconds. Then, the starch is separated from hot air in cyclons. Due to short time of high

temperature drying and intensive water evaporation from the starch granules, it’s surface is

heated only to 40°C.

Dried starch contains about 21% of water. During the pneumatic transport starch looses

additional 1% of water.

Received starch is storing separately in silos, in jute bags (100 kg) or paper bags (50 kg). There

are three kinds of starch: superior extra, superior and prima. Different sorts of starch depend on

degree of purity and whiteness. The differences between them are in an acidity and content of

mineral substances.

Table 1. Potato starch production characteristic.

Processing 2.000 t per 24 hours

Ratio of starch extraction 87%

Water expenditure:

- washing

- technological

6.5m3/t

2.5m3/t

4.0m3/t

Water steam expenditure 400 – 500 kg/t starch

SO2 expenditure 0.8 kg/t potatoes

Yield: per ton of potatoes (16,8%) 175 kg starch

Loss:

- potatoes losses (transport and washing)

- pulp starch losses

-juicy water starch losses

about 10%

0.5%

8 – 9%

1.0%

The water which is used in starch production (dirty water) for transportation and cleaning

doesn’t have to be totally clean. That’s why clarifier usage enables application of closed cycle

which noticeably reduces amount of cleaning water that is needed. On the other hand,

requirements for quality of technological water are the same as for drinking water

(microbiological and chemical contamination). In addition, this type of water should contain low

amounts of metals such as: Ca, Mg, Fe, Mn; which has bad influence on starch properties.

Waste products

Potato juice - is a liquid waste product separated from the potatoes pulp using centrifuges or

decanters. It contains about 5% of dry substance, including about 2% valuable protein, of high

nutritional value, minerals, vitamins and other. In modern starch plants separation of the juice

from the mash is used. We can get about 600 kg of coagulated protein from each 1000 kg of

potatoes. The final product contains about 80% protein (with the digestibility of about 90%),

2.5% minerals, 1.5% fat, 6% nitrogen-free substances and 10% water. Because of the full range

of the egzogenicamino acids the formulation is a valuable protein feed.

Potato pulp is a side product of washing the starch from the mash. It contains all non-starchy

substances insoluble in water (fragments of wall of cells) and bounded starch which cannot be

mechanically separated from the blended parties of potato. The pulp contains 30% of starch,

which is not extracted because of economical reasons. That’s why the pulp is often used in

animal feeding. The pulp contains a lot of water and inconvenient in transportation and storage.

That’s why it is really often dried and dehydrated.

Juicy water is a liquid side product obtained after refining of starch milk. It is ten times diluted

potato juice. Due to this fact, it is a sludge and it cannot be discharged to open water.

A general flow chart of

starch production

Industrial Application

Papermaking

Paper industry is one of the largest users of starch. Starch is, in fact, the third most prevalent

raw material component in paper, only surpassed by cellulose fiber and mineral filler.

Depending on the type of

paper produced, starch

content in the final

products may be as high

as 10% by paper weight.

Starch used in paper

manufacture is generally

found in three application areas which are wet end internal sizing, surface sizing and coating.

The general components of paper machine are illustrated in Figure 1. In the paper making

process, a dilute suspension of fiber (0.5-1%) and chemicals are pumped to the head box which

feeds the fiber suspension evenly onto the moving wire conveyor belt. Large amount of water is

drawn away as the fiber suspension moves along with the wire conveyor belt. At the end of the

wire section, a moist sheet of paper is formed. It is then passes through a series of pressing

cylinders where more moisture is removed. The remaining water in the paper sheet is further

removed in the drying section where the sheet is passed over a large number of steam-heated

drying cylinders. At this point, the sheet is almost completely dry.

Way down in the drying section is the size press where a starch paste can be applied on the

paper sheet to improve surface properties. Following the size press, the sheet is dried again. If

coated papers are produced, the pigment coating may be applied at this point. In some cases,

the coating may be performed on an off-machine coater (not integral to the paper machine). The

paper is then passed through a vertical series of hot polished iron rollers (called calenders) to

smooth and polish the surface. The paper sheet is finally wound onto reels for further

processing if desired.

Figure1: Papermaking machine

     Starch can be employed during papermaking process in three main areas:

1. Wet end refers to the portion of the process which contains cellulosic pulp fiber and

other small particle components (such as cellulosic fine, fillers, etc.) dispersed in a large

volume of water. Starch is commonly added in the wet end of the paper machine to

serve as a retention and dewatering aid. Although native starch can be used, cationic

starches have been preferred wet-end starch additives. By being positively charged,

they are attracted to the negatively charged cellulose fiber and the negatively charged

fillers. This increases fiber-to-fiber and fiber-to-filler bonding; thus, promoting a high

degree of filler retention as well as strength increases at low application levels compared

with native starch (Lawton, 2000). The cationic starches that are commercially available

are the tertiary amino or the quaternary ammonium derivatives. While the quaternary

ammonium starches carry a cationic load in all pH ranges, the tertiary amino starches

are only cationic in the acid range. Therefore their possibilities of application are limited.

As a result of the progressive conversion from an acid to an alkaline operation in the

manufacture of paper and the increased use of calcium carbonate in the wet end

system, the use of tertiary amino starches is diminishing (Hellwig et al., 1992).

2. Surface sizing In the paper industry, the largest volume of starch is used for surface

sizing. Surface sizing is an operation in which paper runs through a sizing solution and

then through sizing rolls. These rolls press the sizing into the paper and remove the

excess from the surface of the paper. The main purpose of surface sizing is to improve

surface properties, to give a better writing and printing surface and to minimize linting.

The concentration of starch in a sizing solution can range from 2 to about 15%

depending on the type of size press machine and product requirements (Maurer, 2001).

Cooked unmodified starch is too high in viscosity for most sizing operation; thus the

viscosity of the starch paste is usually reduced. This can be done at the paper mill by

either enzyme or thermochemical conversion. However, these depolymerized starches

have tendency to retrograde or reassociate resulting in a less sizing performance.

Alternatively, preconverted or modified starches may be obtained from the starch

manufacturers. Oxidized starch is one of the most common modified starches for use in

surface sizing because of its good film forming characteristic and reduced tendency to

retrogradation. However, when the paper is recycled, oxidized starch which contains

negative charge can act as a dispersant and contribute to the loss of filler and the starch

itself to the waste water causing pollution problem. Substituted starches such as

acetylated starch, hydroxyethylated starch and cationic starch are gaining popularity in

surface sizing operation. Beside their benefits of reduced retrogradation, these starches

do not cause filler dispersion if the paper is repulped in the recycled process system.

Fugure 2 Scanning electron micrograph of starch acetate nanoparticles

3. Paper coating In paper coating, a layer of pigment, adhesive and other supplementary

materials is applied to the surface of paper. Coating provides whiteness, brightness,

gloss and opacity to the paper as well as a smoother and more uniform surface. Pigment

is the primary material for coating paper. The most commonly used pigments are clay,

calcium carbonate, titanium dioxide and talc. In paper coating operation, starch is used

as an adhesive or binder to bind the pigment particles to each other and to the paper.

Starches used for surface sizing as described above can be used as coating binder as

well. However, coating starches need to have lower viscosities than starched used in

other segments in the paper industry. This is because there is a need for the presence of

high amount of starch in coating formula to provide strong binding for the pigment and at

the same time the coating should still be leveled and applied as a film on the paper

surface. As previously mentioned in surface sizing section, the negative charge of

oxidized starch could contribute to the loss of pigment filler if the finished paper is

repulped; thus, the popularity of oxidized starch as a coating binder has been declined.

Hydroxyethylated starch is considered one of the best materials for use as coating

binders due to its excellent film forming properties and strong resistance to

retrogradation. However, higher cost usually limits its use in the conventional coatings.

Corrugated board adhesives

Corrugated board adhesives are the next largest application of non-food starches globally.

Starch glues are mostly based on unmodified native starches,

plus some additive such as borax and caustic soda. Part of the

starch is gelatinized to carry the slurry of uncooked starches and

prevent sedimentation. This opaque glue is called a SteinHall

adhesive. The glue is

applied on tips of the

fluting. The fluted paper is pressed to paper called

liner. This is then dried under high heat, which causes

the rest of the uncooked starch in glue to

swell/gelatinize. This gelatinizing makes the glue a fast

and strong adhesive for corrugated board production.

Clothing starch

Clothing or laundry starch is a liquid that is prepared by mixing a vegetable starch in water

(earlier preparations also had to be boiled), and is used in

the laundering of clothes. Starch was widely used in Europe in the 16th and 17th

centuries to stiffen the wide collars and ruffs of fine linen which surrounded the

necks of the well-to-do. During the 19th century and early 20th century, it was

stylish to stiffen the collars and sleeves of men's shirts and the ruffles of

girls' petticoats by applying starch to them as the clean clothes were being ironed.

Aside from the smooth, crisp edges it gave to clothing, it served practical purposes

as well. Dirt and sweat from a person's neck and wrists would stick to the starch

rather than to the fibers of the clothing, and would easily wash away along with the

starch. After each laundering, the starch would be reapplied. Today, the product is sold

in aerosol cans for home use.

Application of potato starch

The usage of raw starch is relatively small. Starch is mainly used as material both in the

manufacture of food and non-food products. In food processing a lot of starch is converted to

starch hydrolysates. Also it is used to receive puddings, jellies, desserts, caramel and other food

products. In addition, starch is processed to modified starch in order to change material

properties. The modified starches have a wide range of applications in many industries.

Applications of starch in non-food sectors include: production of dextrin and adhesives, drilling

fluids, biodegradable plastics, gypsum binders and many other. In addition modified starches

are used as fillers, emulsion stabilizers, consistency modifiers etc. Other important fields of

starch application are textiles, cosmetics, pharmaceuticals and paints.

Conclusion

Although the consumption of starch by the paper industry is presently high, many

synthetic materials are available that can substitute for

starch. With an increasing demand for higher paper

properties and rapid advancements in papermaking

technology, these synthetic substitutes are often preferred

especially for the production of high grade paper due to

their higher performance. Currently this challenge can be

met by many advantages that starch has to offer.

Starch is an inexpensive raw material obtained from a

renewable resource. It is a natural polymer with high molecular weight that can be

chemically or physically modified to adjust its rheological characteristics and to provide

a specific performance. Furthermore there is a current global trend on consumer

consciousness to protect world environment which discourages the use of synthetic

materials in many applications and promotes their

replacement by natural organic compounds. This

environmental trend is opening up new product

opportunities for starch in the paper industry. For

example, starch-based pigments have recently been

developed from starch acetate nanoparticles (Figure 2) to

replace the mineral pigment filler (Karvinen et al., 2007).

Starch-graft-copolymer has been developed to produce

new materials with properties that combine the advantages of natural and synthetic

polymers (Maurer and Kearney, 1998).

     With a continuing progress in modification technology, the development of new

materials from starch with specialty characteristics seems to be unlimited. As a result,

the potential of starch as an important raw material in the paper industry remains

promising both at present and in the future.

References

1. http://en.wikipedia.org/wiki/Starch

2. http://en.wikipedia.org/wiki/Biodegradable

3. http://en.wikipedia.org/wiki/Starch_production

4. http://www.tappi.org/Downloads/unsorted/UNTITLED---05AUGSO40pdf.aspx

5. http://www.thaitapiocastarch.org/article17.asp

6. http://www.cargill.com/products/industrial/papermaking/coating/

7. http://www.paperacademy.net/815/paper-chemical-additives/paper-starch-specialty-paper/

8. http://bioplast.com.hk/resin.htm

9. http://www.bioplast.com.hk/