Chem109

POLYMER

S

Polymer are long chain giant organic molecules assembled from many small molecules called monomers . • More monomer molecules joined in units of long polymer.

CLASSIFICATIONS OF POLYMERS Thermoplastics Thermosets Long chain Polymers Natural polymers Homopolymer Copolymer

Properties of Polymers The physical properties of a polymer, such as its strength and flexibility depend on: • Chain length - in general, the longer the chains the stronger the polymer; • Side groups - polar side groups give stronger attraction between polymer chains, making the polymer stronger; • Branching - straight, un branched chains can pack together more closely than highly branched chains, giving polymers that are more crystalline and therefore stronger; • Cross-linking - if polymer chains are linked together extensively by covalent bonds, the polymer is harder and more difficult to melt.

Characteristics of Polymers Low Density. Low coefficient of friction. Good corrosion resistance. Good mould ability. Excellent surface finish can be obtained. Can be produced with close dimensional tolerances. Economical. Poor tensile strength. Low mechanical properties. Poor temperature resistance. Can be produced transparent or in different colours

RUBBE

R

Rubber is a natural polymer of Isoprene (usually cis- 1,4-polyisoprene) Rubber is also known as an elastomer. It can be defined as a sticky, elastic solid Natural rubber - Produced from a milky liquid known as latex Synthetic rubber- Produced artificially.

Types of Rubber Natural Rubber

Latex Coagulated by weak acetic acid after removing the impurities. It is then passed through rollers to get creep rubber. It is then processed to get commercial rubber compounds. Synthetic Rubber

General purpose synthetic rubber Stryene Butadiene Rubber (SBR)

Special purpose synthetic rubber Have special qualities to suit different purposes Neoprene

Characteristics of rubber

Flexible, Elastic Not transparent Water proof/repellence Hard, Strong Insulate electricity Acid & alkaline resistant Doesn’t conduct to heat

Properties Physical Properties

Non reactive Chemically Resistant to many

fluids including many water, weak acids & alkalis

Non conductive Poor conductor of heat & electric Elastic Tough Electric resistant Electric insulator

Chemical Properties

Polymers Consists of isoprene molecules

fitted together in loosed chains Consisting long chains of one or

more type of molecules Contain long chains of hydrogen

and carbon molecules Rubber go through vulcanization

through adding sulfur which result in a hard, durable material with great mechanical properties.

Functions Sustainability

Rubber has many uses that makes rubber & recycled rubber products a valuable sustainable material.

Rubber is being used as repairing material in United States Pave roads & bridge

Surface of roads are upgraded with ground rubber material

Playgrounds with rubber flooring Not only safer but its own aesthetic value

Used & re-purposed for protective gear

Create fibers for clothing & outerwear

Lower the budget in construction

Green Materials/ Eco Friendly Materials

Rubber is produced naturally which is a definite green material as rubber recycling has become more common.

There is market demand which keeps vast amounts of rubber out of landfills

Importance of Recycled Rubber Reclaiming & recycling rubber uses less

energy than producing a new rubber. Recycling rubber reduces the demand for

new natural rubber which may keep rubber tree plantations from expanding into sensitive tropical ecosystems.

Keeping rubber out of landfills protects environments as well as human health

• Tire fires in landfills will cause pollution &

pose a significant safety hazard.

AestheticValue

Can be obtained in different types of color Have great eye appeal

Easily shaped, hence allow designer to create seamless installations More safety

Comfortable Hygienic

Can also be engineered with antimicrobial properties

Durability

Vulcanization Forming cross-link between polymer

chains Less sticky, more durable (Vulcanized rubber) • Tires, shoe soles, hoses, conveyer

belts & hockey pucks (Hard vulcanized rubber) • Bowling balls, saxophone mouth

pieces Can be called ebonite & vulcanite

Nature of the rubber Can be compressed & stressed NON reactive to acid & alkaline Heat & electrical insulator

Application Rubber flooring

Used to a large extent in public and industrial buildings because of their good wearing qualities, resiliency (i.e., elasticity) and noise insulation.

Made up of pure rubber mixed with fillers, such as cotton fibre, granulated cork or asbestos fibre and the desired colouring pigments.

Manufactured in the form of sheets or tiles, in a variety of patterns and colours.

Rubber Adhesive Most all rubber-based glues and

bonding agents are made of rubber mixed with other compounds.

Suited as a bonding element because of its flexibility.

Some types of bonding compounds made with rubber are used as sealants.

However rubber adhesive is extremely flammable. • It is not suitable for bonding in high

temperature situations • It is generally used where dampness is an

issue because of its water resistance. • might be damaged by other solvents, such as

oil and grease, and not suitable for bonding heavy pieces.

Bearings pad

Used extensively in standard construction applications, buildings & structural steel bearings applications.

Synthetic fibres are added to the base rubber compounds to create an internal stiffening like steel reinforced concrete.

Rubber bearing pads has been used in: • Bridge bearing masonry pads• Handrail bearing pads • Pads between steel beams,

girders, grates & columns • Pads between bridge and roof

beams and substructures• Shock and vibration isolation • Heavy equipment mounting pads• Railway tie pad applications• Pads underneath concrete vaults

Expansion joints A mid-structure separation which

designed to relieve stress on building materials caused by building movement by:• Thermal expansion & contraction caused

by temperature changes, • Sway caused by wind,• Seismic events

It marks a gap through all building assemblies including walls, floors, decks, planters & plazas, etc. because the joint bisects the entire structure.

Used to bridge the gap & restore the building assembly functions while being able to accommodate the expected movements.

Both natural & synthetic rubber is not widely use in the construction industry.

However, it is mainly used in household & industrial products

Therefore, rubber industry have a bright future for rubber industry.

RUBBER PROCESSING AND PRODUCTS

• 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

Rubber Processing and Shaping• Production of rubber goods consists of two basic steps: 1. Production of the rubber itself Natural rubber is an agricultural crop Synthetic rubbers are made from petroleum 2. Processing into finished goods, consisting of: (a) Compounding (b) Mixing (c) Shaping (d) Vulcanizing

Compounding• Rubber is always compounded with additives

− Compounding adds chemicals for vulcanization, such as sulfur

− Additives include fillers which act either to enhance the rubbers mechanical properties (reinforcing fillers) or to extend the rubber to reduce cost (non reinforcing fillers)

− It is through compounding that the specific rubber is designed to satisfy a given application in terms of properties, cost, and process ability

Mixing• The additives must be thoroughly mixed with the base rubber to achieve uniform dispersion of ingredients• Uncured rubbers have high viscosity so mechanical working of the rubber can increase its temperature up to 150°C (300°F)• If vulcanizing agents were present from the start of mixing, premature vulcanization would result the “rubber processors nightmare”

Shaping and Related Processes• Shaping processes for rubber products can be divided into four basic categories:

1. Extrusion 2. Calendering 3. Coating 4. Molding and casting

• Some products require several basic processes plus assembly work

− Example: tires

Vulcanization• The treatment that accomplishes cross

linking of elastomer molecules, so that the rubber becomes stiffer and stronger but retains extensibility

• On a submicroscopic scale, the long chain molecules of rubber become joined at certain tie points, the effect of which is to reduce the ability of the elastomer to flow

− A typical soft rubber has 1 or 2 cross links per 1000 units (mers)

− As the number of cross links increases, the polymer becomes stiffer and behaves more and more like a thermosetting plastic (hard rubber)

The Rubber Industries• Production of raw NR might be classified as 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

− The company names include Goodyear, B. F. Goodrich, and Michelin, all reflecting the importance of the tire

Production of Natural Rubber• Natural rubber is tapped from rubber trees (Hevea brasiliensis) as latex

− The trees are grown on plantations 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 rubber, and its content in the emulsion is about 30%• The latex is collected in large tanks, thus blending the yield of many trees together

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

Tires and Other Rubber Products• Tires are the principal product of the rubber industry

− Tires are about 75% of total rubber tonnage• Other important products:

− Footwear − Seals − Shock absorbing parts − Conveyor belts − Hose − Foamed rubber products − Sports equipment