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Carbon In HDPE Answers Water Problem

16 Aug

 source: http://www.plastemart.com/upload/Literature/hdpe100.asp

 Pre compounded PE100 black HDPE pipes: Insurance for long service life

The major challenge before mankind in coming years will be to reach clean potable water to consumers without leakage during transport and without affecting the water quality.
Specified and pre compounded black PE100 pipes have already demonstrated world over that it is the best candidate to accomplish this job over a minimum lifetime 50 – 100 years.
It is necessary to understand the very important role compounding plays in getting the best quality out of specified PE100 materials to derive the maximum lifetime benefits.

Why use black HDPE pipes?
HDPE pipes are transported and stored in open atmosphere for considerable length of time before installation. Many pipes are installed above the ground in open sunlight. The UV rays in the sunlight, on prolonged exposure, breaks the molecular chains of PE and produces free radicals. These free radicals continue the process further. As a result, polyethylene pipes lose their flexibility and toughness over a period of time.

Carbon black is the best and most economic UV stabilizer. Proper quality of Carbon black, properly dispersed and distributed in polyethylene by compounding, can prevent UV degradation of pipes for several years despite storage in the open sunlight.

How much carbon black to be used in black HDPE pipes ?
Different level of carbon black has been added into HDPE and time to degradation has been measured, it is seen that above 2% addition level there is no further increase in time to degradation. If the percentage is increased further, it will act just as an inorganic filler and will make HDPE brittle. Hence 2-2.5% addition level of carbon black is considered to be the optimum addition level.

What quality of Carbon black is to be used for HDPE pipes ?
ISO and European standards for HDPE Water pipes specify that t he carbon black used in the production of black compound shall have an average (primary) particle size of 10 nm to 25 nm. Use of higher size of Carbon black adversely affects the lifetime of pipes. Both ISO 4427 and European standard EN12201 specify that “only compounded materials” should be used for production of PE pipes in order to meet the requirements of quality standards.

What are the dangers of using carbon black Masterbatches with natural PE ?
1) By hand mixing of natural PE granules with a carbon black masterbatch (which is a concentrate of typically 40% carbon black in a very high MFI PE resin) and extruding the mixture in a pipe extruder into pipes, the pipes will surely look black, but there is hardly a good distribution and dispersion of Carbon black for proper UV protection. This is because in a single screw pipe extruder the residence time of material is quite low and intensity of mixing is also less. This may lead to agglomerates of Crabon black in pipe wall which work as crack initiation points.

2) In case of any premature failure of pipes, neither the resin manufacturer, nor the masterbatch manufacture will take the responsibility of failure.

3) It has been seen that using the same natural PE, but different Carbon black Masterbatches, the time to failure in pressure test vary considerably.

4) Carbon black is a material which remains in colloidal form even in molten state. It is very difficult to disperse in a single screw pipe extruder with short residence time. Blending of natural PE with CBMB in the pipe extruder fails to ensure good dispersion and distribution of CB. This leads to poor UV protection, defects in the pipe wall and low long term reliability.

What are the advantages of using black compounds over salt and pepper ?

The manufactures of compounded HDPE pipe materials add carbon black and other additives in masterbatch form to the powder HDPE resin, using sophisticated twin screw compounding machines. The use of powder HDPE and intense compounding ensures proper distribution of carbon black in PE and the compound can be straightway used for production of pipe in a pipe extruder. Also the manufacturer of compound takes full accountability and ownership of the quality of the compound.

Due to demanding needs of modern installation techniques, and tough service requirements, HDPE pipes are required to safeguard against failures initiating from notches on the pipe surface arising at installation and defects in the pipe wall due to inhomogenity of raw material.
High level of product consistency in Pressure Pipes and quality required can only be achieved by using ready made black compounds.

About Borouge
Borouge is the leading suppler of specified HDPE PE100 black compounds for water distribution pipes in Asian market and a prominent member of PE100+ Association. Borouge brings the best of European technology to one of the Middle East’s most modern plants and is rapidly expanding capacity in the polyolefins industry. For more information, please visit www.borouge.com.

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Posted by on August 16, 2007 in General Knowledge, Industrial Plastics

 

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