Understanding and modelling the diffusion process of low molecular weight substances in polyethylene pipes

• Peroxides are widely used as crosslinkers in polyethylene (PE) drinking water pipes. Cross-linked polyethylene (PEX) has better mechanical properties than PE, but peroxide decomposition by-products can migrate from PEX water pipes into the drinking water unless sufficient preventive actions are undertaken. This work systematically examines the migration of tert-Butyl methyl ether (MTBE), a dominating crosslinking by-product from PEX water pipes, into tap water by utilizing both experimental techniques and finite element (FEM) diffusion modeling. The effects of pipe geometry, tap water temperature (23–80 °C), boundary conditions (air or water interface) and degasing (at 180 °C) were considered. The MTBE diffusivity increased strongly with increasing temperature and it was concluded that a desired water quality can be achieved with proper degasing of the PEX pipes. As the FEM simulations were in excellent agreement with the experimental results, the model can accurately predict the MTBE concentration as a function of time, water temperature and PEX pipe geometry, and enable the pipe manufacturers to aid in ensuring desirable drinking water quality.

Subject headings

NATURVETENSKAP  -- Kemi -- Polymerkemi (hsv//swe)

NATURAL SCIENCES  -- Chemical Sciences -- Polymer Chemistry (hsv//eng)

Keyword

Crosslinked polyethylene

Diffusion coefficient

Diffusion model

Drinking water

PEX pipes

Polymers

Diffusion

Oxidation

Peroxides

Phase interfaces

Polyethylenes

Temperature

Water pipelines

Water piping systems

Water quality

Drinking water pipes

Experimental techniques

Increasing temperatures

Low molecular weight

Peroxide decomposition

Tert-butyl methyl ethers

Potable water

deionized water

peroxide

polyethylene

polymer

tap water

tert butyl methyl ether

byproduct

decomposition

molecular analysis

MTBE

pipe

plastic

pollution incidence

water temperature

Article

biodegradation

concentration (parameter)

cross linking

diffusivity

finite element analysis

heat treatment

mass fragmentography

molecular weight

priority journal

process model

simulation

Publication and Content Type

ref (subject category)

art (subject category)