Products of Polyvinylchloride

Polyvinyl Chloride (PVC) piping: This is the most widely used plastic piping material. PVC piping is used for drain-waste-vent (DWV) sewers, water mains, water service lines, irrigation, conduit, various industrial installations. It can be used under ground or above ground in buildings. It can also be used outdoors if the pipe contains stabilizers and UV inhibitors to shield against ultraviolet radiation.

Source: http://www.contractorspipe.com/

Polyvinyl chloride (PVC) tubing: This is a type of plastic tubing that is corrosion-resistant, flexible, and flame retardant. PVC tubing also does not shrink in heat and offers excellent electrical and physical performance. It can be used as a hard plastic or it can be made softer and more flexible by adding plasticizers. This softer form is the type used to make tubing, hoses, and pipelines.

Other products of PVC: Boat fenders, garden hose, electrical wire insulation, vinyl flooring, roof gutter, children's doll and a medical transparent tube.

Glossary
Plasticizers: any of a group of substances that are used in plastics or other materials to impart viscosity, flexibility, softness, or other properties to the finished product.
Stabilizers: The stabilizer protects PVC pipe compound and compound polymer chains from
thermally degrading during the extrusion process. (Source: http://www.pwpipe.com/literature/tb/tb-s3.pdf)
Extrusion: The act or process of pushing or thrusting out.

Manufacture of Polyvinylchloride Products

When moulding PVC into products for usage, a few processes are carried out.

• For plastic moulding, molten plastic is injected at high pressure into a mold, which is the inverse of the product's shape.
• For rotation moudling, the moulding process carried out in four steps, especially suitable for hollow parts, parts with low residual stress and thick walled parts. Parts with negative undercuts can be made as well. The required amount of plastic material is poured into the mould which is then closed. While rotating around two axes the mould is first heated to the melting-point of the plastic and then cooled again.
• For blow moulding, which is a method used for hollow parts of all sizes, a tube of molten plastics is extruded into an open mould. The mould closes and thereby the bottom of the part welds. Hot air is blown into the tube and it is blown up until it fills out the mould cavity.

An example of a product of polyvinylchloride: a children's doll.

Introduction to manufacturing process of a children's doll: Two major plastic forming processes are used. The heads and limbs are made by rotational molding, producing hollow, seamless products of all sizes and shapes with uniform wall thickness. Blow molding is sometimes used to make the torso if cost is an issue since it is a faster, more economical method.

The processes involved in the manufacture of a children's doll are as follows:

1. During rotational molding, the mold cavities are first filled with a predetermined amount of the compound, in liquid form. Each metal mold consists of multiple cavities and the quantity depends on the size of doll.
2. After the molds are closed, they are placed in a heated oven and rotated biaxially. During the heating cycle, the resin melts, fuses, and then densifies into the shape of the mold cavity.
3. Next, the molds are slowly cooled inside a chamber using air and water. Once cooled, the molds are removed from the chamber, opened, and the finished part is removed
4. Finally, during blow molding, a hollow tube called a parison is first formed out of molten plastic by extrusion through a tubular reservoir.
5. This tube is then placed between two halves of a steel mold and forced to assume the shape of the mold cavity by use of air pressure. The air pressure, ranging from 80-120 psi, is introduced through the inside of the tube, forcing the plastic against the surface of the mold.
6. With a few trimmings and decorations, the doll is produced (in bulks).

Glossary/Summary
Blow molding: a technique for making hollow objects, such as bottles, by injecting air under pressure into a molten mass of glass or plastic and shaping the object within a mold.
Rotational molding: a method for molding hollow plastic objects by placing finely divided particles in a hollow mold that is rotated about two axes, exposing it to heat and then to cold.

Reflections-knowledge acquired from other subjects

In the process of our research, we have learnt a wide range of facts about the 2 chemicals, cellulose acetate and PVC.


Firstly, the industrial processes that are required in the manufacture of the chemicals give us new insight as to how things are done on a large scale, comparative to what we normally do in Science practicals. For example, the volumes of liquids and masses of solids used are so large. We fully understand that the production of these useful products with such widespread applications have great economical value and are money making enterprises. As such, we have learnt many methods that industries have used to speed up the rate of reaction, for example carrying the reactions out in high temperatures and pressures, and using catalysts. Therefore, this SIA has enabled us to look at the entire picture of actually producing chemicals, providing us with a whole new insight to the issue.


Secondly, we have realized how interrelated our 3 Sciences are through this SIA. In life, the search for information, no matter the type, has its ultimate purpose in improving our standard of living by improving technology around us. Thus, much research and effort has been put into creating better products, but how can this be achieved without researching on basic chemicals like cellulose acetate and PVC? The same goes to Physics, where the basis of a dynamo is the principle of electromagnetic induction, that of a casette tape is its coat of fine magnetic powder. In Biology, the hot topics are stem cell research, proteomics, which all have wider implications in searching for cures to diseases.


In conclusion, this SIA has enabled us to acquire knowedge not only within the boundaries of Chemistry, but it has also set us thinking on issues that we have never thought of.