This document provides an overview of rubber processing operations. It begins by defining rubber as a material that can be stretched and returns to its original shape. Natural rubber comes from the latex of rubber trees, while synthetic rubber is produced from petrochemicals. Natural rubber is too soft on its own. The key process is vulcanization, discovered by Charles Goodyear, which involves adding sulfur to produce cross-linking that makes rubber stronger and more elastic. The two basic steps in production are making the raw rubber, and then processing it through compounding, mixing, shaping and vulcanizing into finished goods like tires.

1. EPT311
Rubber Processing Operations
Lecturer: Mr. Kudzai Hamish Ruzvidzo
vakudzaihamish@gmail.com
Phone number - 0719121469

2. HIT EPT311 Lecture # 1
RUBBER PROCESSING OPERATIONS
1. Introduction to Rubber
2. Natural Rubber
3. Overview of rubber processing operations
Email: hitruzvidzo@gmail.com
Password: rubber311

3. What is Rubber?
• Rubber is an example of an elastomer type polymer, where the polymer has
the ability to return to its original shape after being stretched or deformed
• In these Rubber Processing Operations series, we define rubber as ‘a
material that can be stretched or compressed and when the force is removed,
will return quickly to its original shape’ without permanent deformation
• The main chemical building blocks of rubber are elastomers, or “elastic
polymers.” These are large chainlike molecules, which when cured
(vulcanized) form chemical crosslinks between the polymer chains.
• The first common elastomer was Polyisoprene, from which natural rubber is
made.
• In general, rubber materials are characterized by their low modulus of
elasticity. They are resistant to water, alkalis and weak acids. Rubber is also
a good electrical insulator, and can be used as a bonding agent.
• In 1770 Joseph Priestley coined the term rubber.

4. Rubber Products

5. Types of Rubber
• There are two types of rubber: natural and synthetic.
• Natural rubber is produced from the latex (milky juice) of the Hevea
Brasiliensis tree.
• It is, therefore, a renewable resource unlike synthetic rubber, which is
manufactured from petrochemicals
• Natural rubber is harvested as latex – a natural source of isoprene, called
caoutchouc or India rubber – which is dried out for commercial processing.
• This dried out form of natural rubber is the chemical Polyisoprene.
• Although it has some elasticity, Polyisoprene is normally mixed with
chemicals and vulcanized to produce the finished product. Natural rubber is
both elastic and viscous making it an ideal polymer for dynamic and static
engineering applications.

6. Natural rubber is too soft to be used in most applications.
When natural rubber is stretched, the chains become elongated and slide past each other until the
material pulls apart.
In 1939, Charles Goodyear discovered that
mixing hot rubber with sulfur produced a
stronger more elastic material. This process is
called vulcanization.
Vulcanization results in cross-linking of the
hydrocarbon chains by disulfide bonds. When the
polymer is stretched, the chains no longer can slide
past each other, and tearing does not occur.
Vulcanized rubber is an elastomer, a polymer that stretches when stressed but then returns to its
original shape when the stress is alleviated.
disulfide bond
disulfide bond
disulfide bond

7. Milky fluid
Has odour
Sticky

8. Hevea brasiliensis
 Most common source
Produces cis-1,4-polyisoprene
 Native to Amazon Rainforest
Gutta-Percha
 Produces trans-1,4-Polyisoprene
Native to Malaysia
Trans-1,4-polyisoprene
gutta-percha

9. Overview of Rubber Processing
 Many of the production methods used for plastics are also applicable
to rubbers
 However, rubber processing technology is different in certain
respects, and the rubber industry is largely separate from the plastics
industry
 The rubber industry and goods made of rubber are dominated by one
product: tires
 Tires are used in large numbers on automobiles, trucks, aircraft,
and bicycles

10. Two Basic Steps in
Rubber Goods Production
1. Production of the rubber itself
 Natural rubber (NR) is an agricultural crop
 Synthetic rubbers is based on petroleum
2. Processing into finished goods:
 Compounding
 Mixing
 Shaping
 Vulcanizing

11. The Rubber Industries
 Production of raw NR is an agricultural industry because latex,
the starting ingredient, is grown on plantations in tropical
climates
 By contrast, synthetic rubbers are produced by the petrochemical
industry
 Finally, processing into tires and other products occurs at
processor (fabricator) plants, commonly known as the rubber
industry

12. Production of Natural Rubber
 Natural rubber is tapped from rubber trees (Hevea brasiliensis) as latex
 In Southeast Asia and other parts of the world
 Latex is a colloidal dispersion of solid particles of the polymer
polyisoprene in water
 Polyisoprene (C5H8)n is the chemical substance that comprises NR, and
its content in the emulsion is about 30%

13. Recovering the Rubber
 Preferred method to recover rubber from latex involves coagulation -
adding an acid such as formic acid (HCOOH)
 Coagulation takes about 12 hours
 The coagulum, now soft solid slabs, is then squeezed through rolls
which drive out most of the water and reduce thickness to about 3
mm (1/8 in)
 The sheets are then draped over wooden frames and dried in
smokehouses for several days

14. Grades of Natural Rubber
 The resulting rubber, now in a form called ribbed smoked sheet, is
folded into large bales for shipment to the processor
 In some cases, the sheets are dried in hot air rather than
smokehouses, and the term air-dried sheet is used
 This is considered a better grade of rubber
 A still better grade, called pale crepe rubber, involves two
coagulation steps, followed by warm air drying

15. Synthetic Rubber
 Most synthetic rubbers are produced from petroleum by the same
polymerization techniques used to synthesize other polymers
 Unlike thermoplastic and thermosetting polymers, which are
normally supplied to the fabricator as pellets or liquid resins,
synthetic rubbers are supplied to rubber processors in the form of
large bales
 The rubber industry has a long tradition of handling NR in these
unit loads

19. End of Lecture 1
Lecture 2 will focus on:
 Mastication of natural rubber (NR)
 Importance of rubber mastication with respect to molecular weight, chain length and
properties of the final rubber
 Use of peptisers and presence of oxygen in rubber mastication