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Manufacture Polypropylene Pipes and PVC pipes

Manufacturing of Polypropylene Pipes:
Polypropylene Pipes (PP) pipes and PPR pipes are manufactured by extrusion in the same way as PE pipes. Particularly in the case of PP pipes  there are several different molecular structures available on the market. In the simplest case the molecular chain is built up of one and the same repeating unit often the same as the monomer shown within the brackets). The polymer is then called homo-polymer. If instead the molecular chain is built up of two different repeating units( A and B) the polymers is called copolymer. In the case of PP the homo-polymer, often designated to PP-h, the repeating unit A is the monomer propylene. In PP copolymers, designated to PP-c, the unit B is the monomer ethylene. Dependent on how the repeating units A and B are arranged in the molecular chain, distinction is made between alternating, copolymers: “ABABAB...” (PP-c), block copolymer :”AAAA....BBBB....AAAA....” (PP-b) and random copolymers “AABABBAABBAAA.....”(PP-r). In the later case the copolymer is built up at random by the units A and B.

The stiffness of the PP pipe will decline in the order: PP-h-PP-b-PP-r and consequently the impact strength will increase simultaneousness. It has also been found that the long-term strength at elevated temperature: (600 C ) will increase when going from PP-h to PP-r most commonly used for PP sewer pipes and for cold water pipes id PP-b . Particularly for sewer pipe purpose new high molecular weight resins have been developed recently. The melt flow rate expressed as MFR 230/2 may be in the range of 0.3g/10min. This value corresponds approximately to 0.6 expressed as MFR 190/5 normally used for PE. The most significant property for these new PP grades from a practical point of view as far as buried pipes is concerned, is the rather high short term E- modulus; i.e. Approximately 50% above corresponding values for the most common PE grades. The density of the PP compound is lower than for corresponding PE resins, or approximately900kg/m3 as compared with 950-960kg/m3 for PE. The designation for these polyethylene resins is PP 80.

By improvement of PP-r grades high temperature resistant hot tap water pipes have been introduced recently. They can compete with PEX and PB for many hot water applications, but are easier to process than PEX and safer than PB as far as strength reproducibility is concerned. Furthermore, the PP pipes can be jointed by welding , which is not the case with PEX.

Manufacturing of Polyvinyl Chloride Pipes: Polyvinyl Chloride Pipes (PVC ) and PPR pipes can be manufactured with or without plasticizers. Examples of the former are garden hose, floor tiling and household articles. The addition of plasticizers increases material flexibility, but leads to some deterioration in other physical properties. Furthermore, some plasticizers display a tendency to migrate, escaping in the course of time so that the plastics becomes brittle. For these reasons, no pastiches are used in the manufacturer of PVC pipes for water mains and sewers. In this respect, the material is characterized as rigid PVC and this variety is termed PVC-U ( unplasticized PVC) according to ISO.

As in the case of PE, where melt flow rate describes the molecular weight of the material, PVC makes use of what is termed the K- value, It may be determined in various ways , but in the following pages consideration is given to the value obtained in accordance with the Fikentscher method, based on 1% PVC in Cyclohexanone at 25 C. A K-value of 65 determined in accordance with this method corresponds to viscosity grade of 105 according to ISO/R 174, 1961. K-value increase with rising mean molecular weight of the polymers, i.e. With greater molecule length. As for PE, the strength of a PVC material then improves, but at the same time it becomes more difficult to process. The K-value of PVC pipes normally lies in the range of 65-70, another definitive characteristic of PVC is its softening temperature, as compressed as what is termed the softening point (Vicat Point). Normally this lies between 70 C and 80 C . A rise in softening point leads to improved distortion resistance to heat and as a rule, also improved strength properties.

Distinctions are made in raw materials between emulsion, suspension and bulk resins. Manufacturing processes based on this order of raw materials, ensure, among other things, increased purity and lower water absorption in the PVC material. The most common type is suspension PVC (S-PVC), although emulsion PVC (E-PVC) also exists.

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This article is written by Mr. Yunik Chandna, Director of Fusion PPR, a Leading PPR pipe manufacturer and plastic pipe manufacturer from India