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QUALITY ISSUES RELATED TO

SHEET PROCESSING

S. Mohanachandran NairDirector

Dept of Processing & Product DevelopmentRubber Board India

Type wise Production of Natural Rubber

(World Scenario- 2010)

CountryTotal

Production(‘000 tonnes)

RSS(%)

Latex (%)

Block Rubber (%)

Others(%)

Thailand 3252 25 17 38 20

Indonesia 2736 7 2 89 2

Malaysia 939 - 10 89 1

INDIA 851 71 10 14 5

Vietnam 755 2 10 80 8

WORLD 10401 18 12 65 5

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Type wise Production of Natural Rubber

(Indian Scenario 2011 -12)

TypeProduction

(MT) (%)

RSS 658200 72.84

Block Rubber 119815 13.26

Latex Concentrate (drc) 76490 8.46

Others 49195 5.44

Total 903700 100.00

Type wise Consumption of Natural Rubber

(Indian Scenario 2011 -12)

TypeConsumption

(MT)(%)

RSS 616215 63.90

Block Rubber 248285 25.74

Latex Concentrate (drc) 73190 7.59

Others 26725 2.77

Total 964415 100.00

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• NR in Sheet form is the oldest and most popular type.

• The process of making sheet rubber is relatively simple and commonly used in small holdings and small estates.

Sheet Rubber-Types

ISNR 3LRSS (Ribbed Smoked Sheet)

RSS

Air dried sheet

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• Ribbed pattern imprints into the sheet to increase the surface area to enhance evaporation rate.

• Smoking is mainly to prevent subsequent spoiling by microbes.

• Smoking done at controlled timings and temperatures (40 - 65º C)

GradesRSS classified into 6 major grades

Grades Products Equivalent TSR

RSS 1 X Superior quality extruded items ISNR 5

RSS 1

RSS 2 Extruded items ISNR 5ISNR 10

RSS 3 Tire,Conveyor belt etc

ISNR 10ISNR 20

RSS 4

RSS 5Moulded items –low

priced ISNR 50

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Grading Depends on

• Purity

• Elasticity

• Color

General Specifications

• The rubber must be dry, firm, free of blisters, mould and foreign matter.

• Under-cured, opaque, oxidized spots or streaks, melted sheets are not graded.

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Comparison of Physical and Chemical Properties of Block Rubber & Sheet Rubber

Characteristic ISNR 20(typical)

RSS 4(typical)

Dirt content, % by mass 0.16 0.09

Volatile matter, % by mass 0.46 0.78

Ash content, % by mass 0.78 0.45

Nitrogen content, % by mass 0.36 0.48

Initial Plasticity (Po) 34 42

Plasticity Retention Index (PRI) 58 82

Common defects in RSS

• Foreign matter – Inadequate sieving• Pin head bubbles – Gas forming bacteria and incomplete

coagulation • Discoloration - Enzymic action• Rust (Resinous matter) – Delayed drying

• Mould growth – Inadequate drying and humidity

• Tackiness – Excess acid• Blisters – Excess drying temperature• Rigid sheet – Insufficient dilution

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General defects

ISNR 3L

ISNR 50

Rigid Sheet Fungus

Bubbles

Correcting defects

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Ideally dried sheet

RSS grades depend on Visual Inspection leading to:

High probability of inconsistency in grading

Normal Thickness of sheet is 2.5 to 3.5 mm.

Weight varies from 500 gm to 1300 gm.

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ISNR 3L

Packing

Often overlooked, but critically important

Packed in bundles of 25 kg,35 kg,50 kg and 111.11 kg

International bale packingdone by shrink wrappingmachine to 0.14 cum size weighing 111.11 kg

50 kg

Why bale coating?

• Prevent stickiness of bales• Prevent fungus formation• To stencil grade mark and

supplier code

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As per International Green Book (International

Standards for Quality & Packing of Natural Rubber

Grades, Section - 7) , all sheets including wrapper

sheets should be equal or higher grade.

The permissible limit of bale coating solids is 450

gm for 111.11 kg or 200 gm for 50 kg bundle.

Over coating on bales

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Over coated bale

Adverse ffects of bale coating

∙ Excess ash content adversely affecting

compounded physical properties

• Air pollution and related health hazards

• Doping dust damages electronic

equipments

• Camouflaging inferior sheets with exces

doping

• Manipulation in weight

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Advantages of Polythene packing

• LDPE of melting point below 110o C is consumed in production process

• Zero wastage

• Environment friendly with a cost advantage

• Reduce chances for manipulation in weight

• Polythene stretch wrapping gives bettercompaction

• Identification of suppliers and grades is easier byprinting supplier and color code for grades

• Prevents absorption of moisture

RSS packed in LDPE bags

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Wrapping in stretch film

Thank You for the Attention