Ultra Thin is In with EVOH Pipe

EVOH demand heightens, and prices climb. Maillefer teams up with suppliers so that manufacturers can make more multi-layer PEX or PE-RT pipe with less.

Use of Ethyl Vinyl Alcohol Copolymer (EVOH) has grown significantly over the past years. Its barrier properties have won wide acceptance throughout plastic processing industries, notably packaging (e.g. food, pharma and cosmetics). With few suppliers, heightened demand and climbing prices, the pressure is on heating & plumbing pipe manufacturers to optimize their use of EVOH in their multi-layer PEX / PERT constructions. Maillefer teams up with material suppliers to bring high-performance solutions which allow customers to make more pipe with less EVOH and still come out ahead.

Lowering the mole level

EVOH grades are available with different levels of ethylene content. Measured in mole %, the lower numbered EVOH has improved barrier properties, but rising extrusion complexity. The 27 mol% EVOH offers two to three times more barrier properties in comparison to the commonly used 32 mol% formulation. The 32 mol% type is typically extruded for a layer thickness range between 50 – 100 μm, whereas the 27 mol% can be spread much thinner to achieve comparable barrier properties. The reduction in material consumption is stated to largely offset the cost disadvantage of the 27 mol% grade.

Co-extrusion protects EVOH flow

Because EVOH is hydrophylic, it must be kept away from water and high humidity (e.g. above 60%) during storage and processing. Otherwise, its barrier features are compromised. This risk increases with the lower mol% grades. Material dryness throughout the conveying systems together with Maillefer’s multi-layer co-extrusion process helps ensure water does not get in the way. Once drawn down between the inner and outer-most PEX / PERT layers, the EVOH layer is protected. The extruded pipe then exits from the crosshead and can continue securely downstream through water cooling and conditioning.

Tightening the process for quality

The material change leads to new challenges in the extrusion process. The extra thin layer needs to be perfectly centered, concentric and without thickness variations. The thicker layer of 32 mol% types offers more tolerance. Maillefer helps provide the ideal screw & barrel combination, crosshead design, tooling and control technology to process the more demanding EVOH.

Innovation from the lab, savings in the field

Recent lab runs with a leading EVOH supplier were conclusive. He brought along his material and a target of reaching 18 μm thickness on our five-layer PEX extrusion line. Within the first hours, test results met expectations and beyond. They ended with runs down to 15 μm. In the days that followed, the material supplier reported that all samples, notably the 15 μm ones, had passed the permeability tests.

Chart indicating relative humidity compromising the barrier properties of EVOH

Our long-term cooperation with leading material suppliers is our primary driver in providing innovative solutions. This is proven once again with the EVOH market situation. The more demanding EVOH formulations are making it possible for our customers to design pipe with a much thinner barrier layer and stretch out the given quantity across much longer lengths.

Producing pipe with an extra thin EVOH promises reduced costs for pipe manufactures. Since less EVOH is used per meter of pipe, it is our industry’s response to a limited supply of EVOH worldwide.