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CHAPTER 4: Natural Rubber Industry - Coggle Diagram
CHAPTER 4: Natural Rubber Industry
Introduction
Natural rubber is a polymer obtained from the latex of rubber trees.
Structure name: Cis-1,4 polyisoprene
Appearance of Natural Rubber Latex: Milky fluid , Has odour, Sticky.
Collected in a cup mounted on each tree.
Latex is a colloid: contains suspension of rubber particles in water
Natural Rubber Processing into Final Product
Compunding
Adds sulfur for vulcanization
Additivies include fillers, mainly used reinforcing fillers is carbon black
To protect from ultraviolet radiation
Appear black in colour
To increase tensile strength
other fillers and additives: China clays, Polymers such as styrene, Recycled rubber, Antioxidants,colouring pigments, plasticizers
Mixing
Additives mixed with base rubber
Stage 1: Carbon black & non-vulcanizing additives
Stage 2: Vulcanizing agents after cooling
Filament reinforcement such as cellulose reduce extensibility
Vulcanizing
A process when chemical crosslinks are introduced to tie the molecules together to form 3D network.
Some C-H bonds are replaced by chains of sulfur atoms link with a cure site of another polymer chain.
Shaping
Calendering
Feedstock become less thick called sheetstocks after passed through rotating rolls
Coating
Important industrial process for producing automobiles tires, conveyor belts
Extrusion
Forcing uncured rubber through a die under pressure to form a shaped sheet
Molding and casting
Tire production, shoe sales and heals, gaskets and seals, suction cups
Principal molding process: Compression, Transfer, Injection
Tires and Rubber Product
Tire Construction
Hose
Footwear
Rubber components: Soles, heels, rubber overshoes
Plain hose is extruded tubing
Reinforced tube consists of inner tube, reinforced layer , outer layer
Internal stucture: Carcass (multiple layer of plies)
Basic tire constuctions: Diagonal phy, Belted bias, Radial ply
Physical and Chemical Properties of Raw Natural Rubber
Chemical Properties
React with Hydrogen: Formation of Hydrogenated rubber
React with Chlorine: Formation of chlorinated rubber
Contains antioxidants, stable for longer storage periods
Physical Properties
Specific gravity: 0.932 at 20C
Specific heat: 0.502 at 20C
Purified NR after extraction with acetone: Refractive index of 1.5215 to 1.5238
Natural Rubber remains in liquid form because of the membrane is negatively charged and repel with each other and could not coagulater
Coagulation process
Addition with acid
Action of bacteria
Bacteria from air enter the latex, the growth of bacteria produces lactic acid and causes coagulation of latex.
Acids: Methanoic acid/ethanoic acid/formic acid
H+ ion neutralize protein membrane(negative), rubber particles collide each other then breaks the protein membrane and latex coagulates.
Advantages: Cost efficient, rubber elasticity not affected
Production of Natural Rubber
Natural Rubber is tapped from rubber tree
Diluted to 50% with additional water
Coagulated by additing formic acid
Coagulum then squeezed by rollers.
Drying for several days
Folded into large bales for shipment
*DRYING: 3 grades f rubber sheets (Ribbed smoked sheet in dark brown colour, Air-dried sheet, Pale crepe rubber in light tan)