DESIGN METHOD

Research on

By Simiraaj. M.Design (2nd sem)NIFT,Kannur.

What is plastic?

Plastics are a material that is made up mainly of macromolecules, that can be made fluid by the action of heating and pressurizing, and that can be processed into end products with any useful shape you want to make.

Types of plastic• High density polyethylene (HDPE)• Low density polyethylene (LDPE)• Polypropylene (PP)• Polystyrene (PS)• Polyvinyl chloride (PVC)

High-Density Polyethylene High-Density Polyethylene

products are very safe and are not known to transmit any chemicals into foods or drinks. HDPE products are commonly recycled. Items made from this plastic include containers for milk, motor oil, shampoos and conditioners, soap bottles, detergents, and bleaches. It is NEVER safe to reuse an HDPE bottle as a food or drink container if it didn’t originally contain food or drink.

Manufacturing process (1) SLURRY PROCESS : The Ziegler-

Natta catalyst, as granules, is mixed with a liquid hydrocarbon (for example, 2-methylpropane (isobutane) or hexane), which simply acts as a diluent.  A mixture of hydrogen and ethene is passed under pressure into the slurry and ethene is polymerized to HDPE. The reaction takes place in a large loop reactor with the mixture constantly stirred (Figure 4).  On opening a valve, the product is released and the solvent is evaporated to leave the polymer, still containing the catalyst.  Water vapour, on flowing with nitrogen through the polymer, reacts with the catalytic sites, destroying their activity. The residue of the catalyst, titanium(IV) and aluminium oxides, remains mixed, in minute amounts, in the polymer.

• (2) Solution process : The second method involves passing ethene and hydrogen under pressure into a solution of the Ziegler-Natta catalyst in a hydrocarbon (a C10 or C12 alkane).  The polymer is obtained in a similar way to the slurry method.

• (3) Gas phase process :A mixture of ethene and hydrogen is passed over a Phillips catalyst in a fixed bed reactor (Figure 6).Ethene polymerizes to form grains of HDPE, suspended in the flowing gas, which pass out of the reactor when the valve is released

PHYSICAL PROPERTIES• Waxy• Black• Medium clutter• Impression possible• Joining by fusion• Hard

Low-Density Polyethylene

Low-Density Polyethylene is sometimes recycled. It is a very healthy plastic that tends to be both durable and flexible. Items such as cling-film, sandwich bags, squeezable bottles, and plastic grocery bags are made from LDPE.

Manufacturing process•  Low-density polyethylene (ldpe) is a thermoplastic made from

petroleum. It was the first grade of polyethylene, produced in 1933 by imperial chemical industries (ici) using a high pressure process via free radical polymerization. The process is operated under very high pressure (1000-3000 atm) at moderate temperatures (420-570 K) as may be predicted from the reaction equation. This is  a radical polymerization process and an initiator, such as a small amount of oxygen, and/or an organic peroxide is used.

• Ethene (purity in excess of 99.9%) is compressed and passed into a reactor together with the initiator.  The molten poly(ethene) is removed, extruded and cut into granules. Unreacted ethene is recycled.  The average polymer molecule contains 4000-40 000 carbon atoms, with many short branches.

• There are about 20 branches per 1000 carbon atoms.  The relative molecular mass, and the branching, influence the physical properties of LDPE.  The branching affects the degree of crystallinity which in turn affects the density of the material.  LDPE is generally amorphous and transparent with about 50% crystallinity.  The branches prevent the molecules fitting closely together and so it has low density.

Polypropylene

Polypropylene is occasionally recycled. PP is strong and can usually withstand higher temperatures. It is used to make lunch boxes, margarine containers, yogurt pots, syrup bottles, prescription bottles. Plastic bottle caps are often made from PP.

Manufacturing process• Production of polypropylene takes place by slurry, solution or gas phase

process, in which the propylene monomer is subjected to heat and pressure in the presence of a catalyst system. Polymerisation is achieved at relatively low temperature and pressure and the product yielded is translucent, but readily coloured. Differences in catalyst and production conditions can be used to alter the properties of the plastic.

• Propylene is obtained, along with ethylene, by cracking naphtha (crude oil light distillate). Ethylene, propylene, and higher alkenes are separated by low temperature fractional distillation. From being a byproduct of ethylene in the early 1950's, propylene is now an important material in its own right.

Physical properties• Semi-rigid• Translucent• Good chemical resistance• Tough• Good fatigue resistance• Integral hinge property• Good heat resistance

Polystyrene Polystyrene is a synthetic

aromatic polymer made from the monomer styrene, a liquid petrochemical. Polystyrene can be rigid or foamed. General purpose polystyrene is clear, hard and brittle. It is a very inexpensive resin per unit weight polystyrene is commonly recycled, but is difficult to do. Items such as disposable coffee cups, plastic food boxes, plastic cutlery and packing foam are made from PS.

Manufacturing processThere are three types of processes generally used - suspension, solution and mass (bulk) polymerisation. The advantages of the solution route, which can be

continuous or batch operation, are low residual monomer content and high purity polymers. The

suspension route produces polymers of different molecular weights and can make specialist

crystal and high impact grades of polystyrene. The main advantages of the mass process are the

clarity and excellent colour of the resins produced.

Physical properties

Polystyrene is a colourless polymer that is

available in sheet and pellet form. It has poor

chemical resistance and weather ability. It is

also of low impact strength and has a glass

transition temperature. 

Polyvinyl Chloride Polyvinyl Chloride is

sometimes recycled. PVC is used for all kinds of pipes and tiles, but is most commonly found in plumbing pipes. This kind of plastic should not come in contact with food items as it can be harmful if ingested.

Manufacturing process

The chemical process for making PVC involves three steps: first, production of the monomer, vinyl chloride, then the linking of these monomer units in a polymerisation process; and finally the blending of the polymer with additives.

Manufacturing process of plastic products:

Depending on the type of products to be manufactured, different plastic manufacturing processes are employed.

Injection moulding

Plastic extrusion moulding

Thermoforming

Injection Moulding• Material is introduced into the injection

moulding machine via a Hopper.  The injection moulding machine consists of a heated barrel equipped with a reciprocating screw (driven by a hydraulic or electric motor), which feeds the molten polymer into a temperature controlled split mould via a channel system of gates and runners. The screw melts plasticises) the polymer, and also acts as a ram during the injection phase. The screw action also provides additional heating by virtue of the shearing action on the polymer. The polymer is injected into a mould tool that defines the shape of the moulded part. The pressure of injection is high, dependant on the material being processed; it can be up to one thousand atmospheres.  Tools tend to be manufactured from steels, (which can be hardened and plated), and Aluminium alloys for increased cutting and hand polishing speeds.  The costs associated with tool manufacture means that injection moulding tends to lend itself to high volume manufacture. 

Click link to watch video of injection mould: http://www.bpf.co.uk/Data/Image/InjectionMouldingAnimation.swf

Telephone handsets, electrical switches, syringes, DVDs, disposible razor are few examples of products made.

Extrusion Moulding• Plastic extrusion involves forcing

melted plastic through a die into a shape with a fixed cross section. It’s an efficient way to produce many shapes, and is essential in both industrial and domestic product applications. Since the plastic is melted from a solid form and then resolidified, only thermoplastics can undergo extrusion. The properties of this type of plastic make it good for recycling both scrap pieces and post consumer goods. 

• Products made are: pvc pipes, clear plastic film, vinyl siding, insulation of electrical wire

Thermoforming • Thermoforming is a manufacturing process where a plastic sheet is heated to a pliable

forming temperature, formed to a specific shape in a mold, and trimmed to create a usable product. The sheet, or "film" when referring to thinner gauges and certain material types, is heated in an oven to a high-enough temperature that it can be stretched into or onto a mold and cooled to a finished shape. In its simplest form, a small tabletop or lab size machine can be used to heat small cut sections of plastic sheet and stretch it over a mold using vacuum. This method is often used for sample and prototype parts. In complex and high-volume applications, very large production machines are utilized to heat and form the plastic sheet and trim the formed parts from the sheet in a continuous high-speed process, and can produce many thousands of finished parts per hour depending on the machine and mold size and the size of the parts being formed.

Click link to watch : http://bpfmedia.emango.net/Thermoforming_RPC_BPF.swf

Disposable cups, containers, blisters, clamshells etc are few products

Physical property PVC has high hardness and  heat stability of PVC is very

poor, when the temperature reaches 140 °C PVC starts to decompose. Its melting temperature is 160 °C. PVC is a polymer with good insulation property. It is formed in flat sheets in a variety of thicknesses and colors.

Application as : pipes, electric cables, signs, building material, clothing, furniture, healthcare, plasticisers,

Chemical propertiesmaterial Color of

flameodor drips Speed

of burning

remarks

HDPE Blue, yellow tip

paraffin yes slow Floats in water

LDPE Blue, yellow tip

paraffin yes slow Floats in water

PP Blue, yellow tip

sweet yes slow Difficult to get scratch

PS yellow Illuminating gas

yes rapid Dense black smoke with soot in air

PVC Blue, yellow tip

fruity no Very slow Black smoke with soot

THANKYOU