PEX pipe (cross-linked polyethylene pipe) is a high-performance plastic pipe widely used in building water supply, floor heating system and industrial fluid transportation. Its excellent performance comes from its special raw materials and manufacturing process. This article will introduce in detail What is pex tubing made of and cross-linking technology and production process.
The basic material of PEX pipe is high-density polyethylene (HDPE, High-Density Polyethylene), which is a thermoplastic polymer with high strength and chemical corrosion resistance. However, ordinary HDPE is not resistant to high temperatures, so it is necessary to change its molecular structure through cross-linking technology, so that it changes from a linear chain structure to a three-dimensional mesh structure, thereby improving heat resistance, pressure resistance and creep resistance.
1. Basic raw materials: high-density polyethylene (HDPE)
Made from the polymerization of ethylene monomer (C₂H₄)
Has high mechanical strength and chemical stability
Uncrosslinked HDPE can only be used in low temperature environments (<60°C), while crosslinked (PEX) can withstand high temperatures up to 95°C
2. Crosslinkers and additives
In order to enhance the performance of PEX pipes, the following ingredients are also added during the production process:
Crosslinkers (such as peroxides, silanes, etc., depending on the crosslinking process)
Antioxidants (to prevent high-temperature oxidative degradation)
UV stabilizers (to reduce aging caused by sunlight)
Masterbatch (used to distinguish pipes for different purposes, such as red, blue, white, etc.)
The performance difference of PEX pipes mainly depends on the cross-linking method. Currently, there are three main mainstream processes in the world:
|
Type |
Cross-linking Method |
Cross-linking Degree |
Temperature Resistance |
Characteristics |
|
PEX-a |
Peroxide (Engel method) |
70%-85% |
Highest (95°C) |
Uniform cross-linking, excellent flexibility, heat-fusible repairable |
|
PEX-b |
Silane (Moisture cure) |
65%-75% |
Medium (90°C) |
Lower cost, requires hot water catalysis for cross-linking |
|
PEX-c |
Electron beam radiation |
60%-70% |
Lower (85°C) |
Eco-friendly (no chemical residues), but higher equipment costs |
1. PEX-a (peroxide crosslinking method)
Process: HDPE is mixed with peroxide before extrusion, and crosslinked under high temperature and high pressure
Advantages: high crosslinking degree, best heat resistance and creep resistance
Disadvantages: high production cost
2. PEX-b (silane crosslinking method)
Process: HDPE is copolymerized with silane, and then immersed in hot water for catalytic crosslinking after extrusion
Advantages: low cost, suitable for large-scale production
Disadvantages: slightly lower crosslinking degree, and long-term high temperature resistance is slightly inferior to PEX-a
3. PEX-c (electron beam radiation crosslinking method)
Process: After the HDPE pipe is extruded, it is crosslinked by electron beam irradiation
Advantages: no chemical residue, environmentally friendly
Disadvantages: large equipment investment, crosslinking may be uneven when the pipe wall is thick.
1. Raw material mixing: HDPE particles are mixed with cross-linking agents, antioxidants, etc.
2. Melt extrusion: Heat and plasticize through an extruder to form a tube
3. Cross-linking treatment (according to different types):
PEX-a: high temperature and high pressure cross-linking
PEX-b: hot water catalytic cross-linking
PEX-c: electron beam irradiation cross-linking
4. Cooling and shaping: solidify the pipe
5. Quality inspection: check the degree of cross-linking, pressure resistance, dimensional accuracy, etc.
6. Printing and packaging: mark specifications, production date and other information.
|
Property |
PEX Pipe |
PP-R Pipe |
PVC Pipe |
CPVC Pipe |
|
Temp. Resistance |
-40°C~95°C |
0°C~70°C |
0°C~60°C |
-20°C~93°C |
|
Pressure Resistance |
High |
Medium |
Low |
High |
|
Flexibility |
Excellent (Bendable) |
Poor (Requires heat fusion) |
Poor (Rigid) |
Poor (Rigid) |
|
Applications |
Floor heating, Water supply |
Hot/cold water pipes |
Drainage, Electrical conduits |
High-temp fluid transport |
The core material of PEX pipe is high-density polyethylene (HDPE), and its molecular structure is changed through different cross-linking processes (PEX-a/b/c), making it have excellent heat resistance, flexibility and anti-aging properties. Among them:
PEX-a has the best performance and is suitable for high-end floor heating and hot water systems
PEX-b has a high cost-effectiveness and is suitable for ordinary household pipes
PEX-c is environmentally friendly and pollution-free, suitable for food-grade applications
The selection of the appropriate PEX pipe type needs to be determined according to the specific use temperature, pressure requirements and budget.
