Introduction: PP-R is a random copolymer of propylene and ethylene, PP-R pipe is made of PP-R resin by extrusion molding, in the late 1980s and early 1990s to develop the application of plastic pipe products. With its own excellent performance and a wide range of application fields, it has occupied a place in the plastic pipe market and is recognized as a green environmental protection product. However, due to the poor low temperature resistance of PPR pipes, the transportation, installation and use of pipelines have brought certain limitations, especially in winter in northern China. Therefore, how to improve the low temperature resistance of PPR pipeline is particularly important.

First, what is PPR pipeline

PP-R is random copolymer polypropylene, that is, we say type III PP. It is obtained by random copolymerization of propylene monomer and a small amount of ethylene monomer under heating, pressure and catalyst, and is a kind of copolymerization PP. Compared with homopolymer PP, it has excellent impact properties, but the price is higher.

PPR pipe is mainly divided into two kinds: cold water pipe and hot water pipe. It can be used not only for ordinary water pipe pipes, but also for pure drinking water systems. The biggest difference between the cold water pipe and the hot water pipe is the thickness of the pipe wall:

(1) The wall of the cold water pipe is about 2.8-3.5mm, and there is a blue mark line on the outside of the pipe wall;

(2) the wall of the hot water pipe is about 4.2mm, and there is a red mark line on the wall side;

(3) the wall of the hot water pipe is thicker and can be used instead of the cold water pipe, but the cold water pipe can never replace the hot water pipe.

Two, why there is low temperature brittleness PPR pipe

PP-R pipe has a certain low temperature brittleness below 5¡æ, in most places in China, the winter temperature is below 5¡æ, so it seriously affects its performance. So why does this happen?

The ethylene monomer in the PPR molecular structure is randomly distributed into the long chain of propylene, where the ethylene monomer is generally controlled between 3-5%. The ethylene content and the polymerization method of ethylene and propylene determine the characteristics of cold brittleness. This is what we often call the glass transition temperature (Tg). When the temperature is low, the middle branch chain and the connecting segment of the molecular structure are specified and cannot move freely. Therefore, when impacted by the outside, the outside energy can not be converted into internal friction heat energy through movement between the molecules, so it is realized as low temperature brittleness.

The external performance is that in the case of low temperature (especially in winter), the flexibility of the pipe at low temperature is reduced, the rigidity is increased, and the performance is brittleness. Under the impact of external force or excessive accidental load, the pipe may be cracked in a straight line. And the cracking starts from the inner pipe and extends to the outer pipe.

Three, the harm of low temperature brittleness

Because the pipe at a low temperature, will show brittleness. Therefore, it brings certain risks to the transportation, installation and use process.

(1) In the winter transportation process, the pipeline will be impacted by external forces during transportation, resulting in rupture, affecting the use of performance, so the need to increase protective measures, which will cause an increase in costs;

(2) in the low temperature environment, it has brought great inconvenience to the installation of the pipeline and affected the construction efficiency. Therefore, in the winter construction, attention should be paid to the characteristics of low temperature brittleness of building water supply polypropylene (PP-R) pipeline, and formulate the corresponding construction plan.

(3) The biggest danger is potential, winter pipe in transportation, in the construction site and installation process due to external injuries, these defects may not be observed with the naked eye, but there will be brittleness and toughness in the use of the process (when transporting hot water) explosion. Endanger personal safety.

Four, improve the method of low temperature brittleness

(1) Mixed with polyethylene PE, PE's low temperature embrittlement temperature can reach -70 degrees, adding the right amount of PE can change the low temperature resistance of PP, but the addition of excessive PE will affect the hardness and stratification of PP products, PE should be the best linear material.

(2) polyolefin POE toughening, POE has the general characteristics of thermoplastic elastomer, small density, heat resistance, excellent cold resistance, the use of a wide temperature range, is the ideal material to change PP low temperature resistance, usually add 3%-15% can make polypropylene PP reach -20 degrees, the use of POE cold grade to toughen PP, Not only change the original PP more low temperature resistance, impact determination will also increase.

(3) EPDM toughening, EPDM the most important characteristic is its superior oxidation resistance, ozone resistance and corrosion resistance and low temperature embrittlement resistance, the use of EPDM cold resistant particles to change PP cold resistance low temperature can reach -40 degrees. The cost is relatively higher than POE, but the performance can not be compared.

(4)PPR can be blended with PPB, and the low temperature embrittlement temperature of PPB is better than that of PPR, adding an appropriate amount of PPB can change the low temperature resistance of PPR.

(5)PPR can change the low temperature brittleness of the pipe by changing its own crystallization method, mainly changing the cooling temperature of the pipe in the production process.

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