Processing and Products of Rubber, Latex product, Preparation of sugar.

1. Economic Botany
Processing of Rubber
Introduction on Rubber Technology
Rubbers are loosely described as materials which show “elastic” properties. These
materials with long chain molecules known as “polymers” and the combination of
elastic and polymers have led to the alternative name of “elastomers”. Rubbers and
elastomers are considered to perform similar function. Products made from rubber
have a flexible and stable dimensional chemical structure and are able to withstand
under force large deformations.
Rubber technology refers to the science involved in the process of transforming
the rubber or elastomers into useful rubber products such as tyres, mats, etc.
Rubber products can be broadly classified into two types such as raw rubber
products and Latex products.
Overview of Rubber Product Processing: The production process of rubber
products can be compared with plastic products and some of them are similar.
However, rubber product technology is different in many aspects. The basic
technology involved in rubber product processing is mentioned below.
Before knowing the rubber product process, it would be helpful to know about
different type of rubbers and processing of raw rubber which are sent to
manufacturing units for product processing. Basically, there are two types of
rubber namely: natural and synthetic rubber.
Natural Rubber
Natural rubber is tapped from rubber trees as latex. Latex is a colloidal dispersion
of solid particles of the polymer polyisoprene in water. The latex is collected in
large tanks, thus blending the yield of many trees together. The preferred method
of recovering rubber from latex involves coagulation - adding an acid such as
formic acid. This process is helpful in reducing the water content in the latex and
they are drained out to form sheets. The sheets are then draped over wooden
frames and are dried. The resulting rubber, now in a form called ribbed smoked
sheet, is folded into large bales for sending it to the processor. It will be dark
brown in color. There are different grades of rubber based on the quality such as
pale creep rubber which is a better grade involving two coagulation steps
By Nandeesha s Msc,MA,BEd,..
1

2. Synthetic Rubber
Most synthetic rubbers are produced from petroleum by the same polymerization
techniques used to synthesize other polymers.
Rubber is used as a name for 3 categories:
Raw Rubber – This is the prime raw material for any rubber product which
determines the main characteristics of the final product.
Semi-manufactured product - The addition to raw rubber with chemicals and
fillers, to impart desirable properties, is termed compounding. The material is
however still malleable and plastic.
Final product – As a result of vulcanisation process, the rubber compound gets its
elastic properties and gives shape to the final product.
Natural raw rubber and Synthetic rubber have similar characteristics and are
alternatively used in the manufacturing process. However, for few product
categories such as tyre, natural rubber is preferred for their product characteristics.
Product Processing:
There are many types of rubber products such as tyres, mats, moulded products,
extruded products, etc. These rubber products have their unique specification of
manufacturing. However, most of the rubber products are processed with four
major steps and are listed below.
Compounding

Mixing

Shaping

Vulcanizing

1)Compounding
Rubber is always compounded with additives. Compounding adds chemicals for
vulcanization, such as sulfur. Additives include fillers which act either to enhance
the rubber's mechanical properties (reinforcing fillers) or to extend the rubber to
reduce cost (non-reinforcing fillers). It is through compounding that the specific

3. rubber is designed to satisfy a given application in terms of properties, cost, and
processability.
2)Mixing
The additives must be thoroughly mixed with the base rubber to achieve uniform
dispersion of ingredients. If vulcanizing agents were present from the start of
mixing, premature vulcanization would result spoiling the product. To avoid
premature vulcanization, a two-stage mixing process is usually deployed by the
processing units:
1. carbon black and other non-vulcanizing additives are combined with the raw
rubber. The term master batch is used for this first-stage mixture
2. after stage 1 mixing has been completed, and time for cooling has been allowed,
stage 2 mixing is carried out in which vulcanizing agents are added
3)Shaping
This process helps in providing the shape to the product in the required form.
Shaping and related processes for rubber products can be divided into four basic
categories:
1. Extrusion
2. Calendaring
3. Coating
4. Moulding and casting
Some products require several basic processes plus assembly work such as tires
which uses all of the basic shaping process to manufacture the final product.
Extrusion
Screw extruders are generally used for extrusion of rubber. The extruder is used to
give shape to the rubber compound through the die fixed. The rubber is fed from
one end it comes out with the preformed shaped as per the die used. The rubber
has not yet been vulcanized. Some of the end product from this process includes
hoses, rubber beadings, cables, etc.
Calendaring

4. Rubber roll is passed through a series of gaps of decreasing size made by a stand
of rotating rolls. Rubber sheet thickness determined by final roll gap. Some of the
end products include conveyor belts, bonding gum, etc.
Coating
This process is used when a fabric is coated with rubber. The equipment is similar
to calendaring equipment. Some of the products made by this process are
automobile tires, conveyor belts, inflatable rafts, and water proof cloth tents and
rain coats.
Roller Die Process
This process involves a combination of extrusion and calendaring which results in
better quality product than either extrusion or calendaring alone.
Moulding
Moulded rubber products include rubber mats, gaskets and seals, bush, chappal
soles, straps and bottle stops. Also, many foamed rubber parts are produced by
moulding. In addition, moulding is an important process in tyre Production as
well. There are different types of moulding processes followed. The major types
are as follows:
Compression moulding

Transfer moulding

Injection moulding

Compression moulding is the most followed technique for most of the moulded
rubber product and it is used in tire manufacturing process as well. Curing
(vulcanizing) is accomplished in the mould in all three processes. But for other
shaping processes such as extrusion and calendaring, separate curing /
vulcanization process needs to be performed.
Vulcanisation
Vulcanisation is generally a heating process that accomplishes cross-linking of
elastomer molecules, so that the rubber becomes stiffer and stronger but retains
extensibility. During the vulcanization process, the number of cross-links
increases, the polymer becomes stiffer and behaves more and more like a
thermosetting plastic (hard rubber).

5. These are the major standard steps followed in manufacturing of rubber products.
However, each product has their own unique process specification and follows
them during manufacturing.
Latex products:
Latex product processing:
Latex products are the products which are made from the latex tapped from the
rubber trees. There are many products which are made from latex such as
adhesives, gloves, balloons, foam mattress, thread, etc. The general processes
followed in manufacturing of latex products includes:
Compounding (Dispersion)

Dipping

Moulding

Extrusion

Vulcanisation

The function of compounding, moulding, extrusion and vulcanisation are similar
to that of the process explained for rubber products. Compounding is a dispersion
process which is done using a dispersion mill (ball mill, attritor mill, etc). Dipping
is done to give a shape to the product in a former (mould) as per the end product
specification.

6. Preparation of sugar
In the manufacturing process of white sugar having four major steps
1.Cane preparation.
2.Juice extraction.
3. Juice clarification.
4. Crystallization and Centrifuging.
1.Cane Preparation :
The object of cane-preparation is to cut cane into short pieces without juice
extraction.
The matured cane has been harvested according to both maturity test and
date of plantation. The harvested cane transported to factory site.
The transport system of cane should be stabilized for efficient supply of
cane.
The cane unloaded by unloaders and shifted to cane carriers. The cane
passes through the preparatory devices like cane leveler, cane cutter and
Dis-integrator(fiberizer or shredder).
The cane leveller knives are required mainly to even cut of the layer of
cane. They are arranged to work with a high clearance and in consequence
leave to a large portion of uncut cane. Its is also called cane chopper or
cane kicker.
The cane cutter is helps to cut the cane into small pieces of cane. It has
installed before entering the dis- integrator.
The object of Dis-integrator is to complete the Preparation and Disintegration
of the cane, so as to facilitate the completed extraction of juice. The dis-
integrated system is called as a shredder or Fibrizer. It consists of a shaft
carrying hoses to which hammers are used.
2. Juice Extraction:
The following technologies that exist today for the purpose of Juice
Extraction.
Milling Technology.
Diffusion Technology.
Low pressure extraction (LPE) Technology.

7. Milling Tandem:
The prepared cane is feed to mills where it is subjected to repeated heavy
pressure by slowly revolving rollers and the juice is squeezed out. The
bagasse coming out from the first mill is subjected to pressure by the next
mills, which are arranged in a single train. According to factory capacity
designed the rollers sizes and number of rollers sets. Generally following 4
milling or 5 milling tandems (rollers sets).
Hot water used for maximum extraction of juice from prepared cane . It is
also called imbibition water. The cane fibers cells replaced juice with water.
The imbibition water is added to the bagasse going to the last mill. The juice
from last mill is added to the bagasse coming to the penultimate mill and the
juice from the penultimate mill is sent to the preceding mill and so on.
Four or five stages(set of mills) are using for juice extraction in milling
tandem. According to that the milling system called as 4-milling tandem or 5-
milling tandem.
Diffusion Technology:
The prepared cane passed through the Diffuser. The diffuser system consisted
of two types of technologies. They are cane diffuser and baggase diffuser.
This is a process in which water or a solution of lower concentration than the
juice which the cells contain give-up to that water or solution a part or all the
sugar forming the excess of concentration of their juice.
In cane diffusion, sugar extraction from cane is actually effected by rupturing
the cane cell and then washing the ruptured cells with water or juice. As
sugar extraction depends to a great extent on the proportion of cells ruptured
and on the access of the cell contents to the extracting liquid.

8. Low pressure extraction (LPE):
The LPE system is using a train of low pressure (LP) units as main
components. Although these devices resemble a conventional mill train and its
operation, the process lends it self more toward the solid.
Low pressure extraction(LPE) system is a simple device and may be termed
as solid liquid extractor. The prepared cane is received by first module of
LPE rolls containing two pairs of fabricated rollers rotating of spherical roller
bearings driven with AC electric motor through chain and sprocket. Tandem
consists of 4 LPE modules followed by a three roller-dewatering mill which
is mainly used to reduce moisture in bagasse.
The collected juice from juice extraction system is send to process house to
produce sugar. After juice exaction the residue is called bagasse and it is
sent to boiler as a fuel.
The extracted juice called depended upon the technology used for juice
extraction. Generally it is called as mixed juice or raw juice or draft juice.

9. 3. Juice Clarification:
In juice clarification process having the following stages.
Juice heating
Sulphitation
Juice clarification.
Evaporation of the juice
Syrup sulphitation.
Juice Heating : Juice heating normally done by three stages. They are raw
juice heating, sulphited juice heating & clear juice heating. For juice
heating used different types of heaters like tubular heaters, direct contact
heaters(DCH) and plate type heaters (PHE).
Heating of the mixed juice or raw juice (comes from juice extraction
system) before the treatment of lime and sulphitation. Raw juice
temperature maintained around 70 to 75 oC . The heated raw juice sent to
reaction vessel of sulphitor.
Juice sulphitation: It a process of purification of cane juice by employing
milk of lime (MOL) and sulphur dioxide(So2) gas. The juice sulphitor is
called as a reaction vessel. In this vessel lime and sulphur dioxide is added

10. and the finally maintained neutral pH of 7.0±0.1. The juice comes from the
juice sulphitor is called sulphited juice.
Sulphited or Treated juice heating : After completion of reaction in juice
sulphitor again juice heated upto its boiling point is called sulphited juice or
treated juice heating. Sulphited juice temperature maintained around 100 to
102 oC.
Juice Clarifier : The function of Clarifier is to separate insoluble solids in
Sulphited juice, which are in “flocs” by means of settling and allowing
the clear Juice.
The clarification process separates the juices treated into two layers.
1.The clear juice,which rises to the top surface.
2.The mud ,which collects at the bottom.
The clear juice sent to evaporation system and mud sent to further juice
extraction.
The settled mud in clarifier contains sugar. To extract the juice from mud
used filtration technology of vacuum filters or decanters technology.
Evaporation: In the evaporation process, the concentration carried on until
the percentage of solids has reached not less than 70%. The process is
conducted under a system of multiple effect evaporators. That is
concentrating clear juice is called syrup and its about 55 to 65
brix(concentration) and pH is varying from 6.5 to 6.8.

11. 4. Crystallization and Centrifuging:
Crystallization :
After sulphitation of syrup is goes to further process of crystallization. This
syrup boiling process done by vacuum pans. The pan boiling essentially
consist of the further removal of water by evaporation in single effect and
crystallizing out sugar by increasing the concentration.
The function of vacuum pan is to produce and develop sugar crystals
of desired size from syrup or the molasses known as mother liquor.
The Duty of vacuum Pan is
Concentration of feed (syrup or molasses)
Sugar Crystal Nucleation.
Finishing the strike with tight massecuite (Massecuite means it is a mixture of sugar
crystals suspended in the almost exhausted mother liquor.)
The first massecuite obtained from virgin syrup is called A-massecuite and
the mother liquor separated from A-massecuite in centrifugal is called A-
molasses. However this A molasses still contains a high proportion of
crystallisable sugar. It is therefore collected separately and used to build
second strike.
Number of bolings to be used for maximum extraction of sugar from syrup.
The number of boiling mainly depends upon syrup purity. In crystallization
process generally follows the massecuite boiling schemes like
Three massecuite boiling.
Three and half massecuite boiling.
Four massecuite boiling.
The masecuites dropped from vacuum pans to cylindrical or ‘U’ shaped
vessel equipped with slow speed stirring element. The special equipment is
called as crystalliser. The massecuite sent from crystallizers to centrifugals
to centrifuge the massecuite.
Centrifuging :
The machine in which crystals in the massecuite are separated from the
surrounding molasses or syrup by a centrifugal force is called a centrifugal
or a centrifuge.

12. Centrifugal machines are mostly divided in two types.
1.Batch type Centrifugal machine
2.Continuous type Centrifugal machine
Batch centrifugal machine used for high grade massecuite ( A- massecuite)
and continuous machines are for low grade massecuites (B & C massecuites).
The batch centrifugal machines takes feed in batch process. It consists of a
perforated drum or basket revolving on a vertical shaft or axis called as
spindle. The basket revolves within a metallic casing, which catches
the molasses spun off molasses due to the centrifugal force. At the time of
separation of molasses, the sugar washed with super heated wash
water and dropped the sugar in hopper for drying process.
The continuous machine runs at constant speed with constant and
continuous feeding of material giving constant output of sugar and
molasses. The only disadvantage is the crystal breakage in continuous
centrifugals due to it’s very high peripheral speed. So continuous
machines are not preferred for high grade massecuite as crystal size and
shape is the important aspects of sugar in market.
Sugar Drying and Cooling:
White Sugar discharged from centrifugal machine is having 0.1 – 0.4%
moisture and 60-80 oC temperature. The higher moisture and temperature of
sugar form lumps during storage. So the sugar should be dried to a safe limit
i.e. upto 0.04 % moisture and cooled up to 38 to 40 oC.
The sugar drying and cooling operation are carried out with the help hot air
and cold air. For sugar drying process used equipments like Grass
hoppers or fluidized bed hopper or Rotary sugar drier.

13. The dried sugar so obtained consists of heterogeneous crystals and needs to
be well sieved and graded before it is marketed. The grading of sugar done
by sugar grader. The sugar crystal size classification is usually achieved by
using wire mesh or perforated plate through which sugar crystal smaller
than screen aperture may pass, while largest fraction is carried over the
surface.
According to sugar crystal size there shall be divided into L, M , S & SS
grades. Generally the crystal size
L- Grade sugar having 1700 to 2200 micron size.
M- Grade sugar having 1200 to 1700 micron size.
S- Grade sugar having 600 to 1200 micron size.
SS- Grade sugar having 200 to 600 micron size.