One of the most difficult issues in the disposal of vehicles is wire harness recycling. Due to the wide variety of materials contained it has proven uneconomical to separate and recycle each component in the harness.

As a result, the most practical option currently is to burn the entire harness, using the waste heat generated from the combustion of plastics. Only metals (mainly copper) which remain after combustion can be salvaged and recycled.
Incineration of PVC releases hydrogen chloride, however, and unacceptably high levels of dioxins have frequently been recorded. Since PVC tape is the principal wrapping method used in wire harness construction today, an economical alternative is needed to smooth the transition to an easily recycled harness.
So where does that leave automotive manufacturers who currently consume around 150 million square metres of PVC wire harness tape every year? PVC tapes manufacturers are continually tracking the trend towards non-PVC alternatives and one of them - Scapa - has come up with a range of solutions designed to meet future needs in the automotive and other industries. Here's how.
Polyvinylchloride (PVC) is a thermo-plastic polymer which has been mass-produced since 1938. It is low cost and easy to process with high dielectric strength and good resistance to chemicals and moisture.
Harness makers also have their own set of specific demands. The tape needs to be flexible and tear easily for quick and simple application in the vehicle with good unwind to minimise the incidence of repetitive strain injury among the manufacturers' workforce. Tape must continue to perform throughout the lifetime of the vehicle where it will be exposed to heat, cold, vehicle fluids and abrasion. It should not contribute to fogging in the passenger compartment. Tape performance is outlined in a new SAE specification for harness covering materials issued in 2002. The challenge, then, is to develop an alternative to PVC tape which meets existing and future performance and recycling specifications without compromising price.

What's the alternative?

In the early 1980s, the cable business unit of global tapes manufacturer Scapa invested in a significant research programme to offer the world's first zero halogen, low smoke, fire retardant compounds to the international cable industry under the brand name Megolon. Possessing the same electrical, mechanical and processing properties as PVC compounds, but without the hazards, Megolon compounds are now well established in helping to ensure the safe and rapid evacuation of large public areas in the event of a fire. They minimise smoke and eliminate toxic fumes and do not give off damaging corrosive gases, so costly equipment is protected.
The technology has been extended to a toolkit of solutions tailored with the automotive industry in mind. The result is the Autolon range of tapes with the look and feel of traditional PVC tapes. These include general purpose tapes with a rubber adhesive as well as acrylic adhesive tapes for high temperature applications up to 125°C (T3). With good elongation, easy unwind and a fogging number of between 70 - 95 depending on the specific product selected, performance is not in question. But how do these tapes rate in terms of recyclability - the main driver behind their development? Tests have been conducted on the Autolon range to measure their performance under combustion, with very positive results. These were presented at the FISITA conference in Helsinki.
To measure the combustion performance of halogen-free tapes, a selection of products was subjected to a simulated combustion process and gases/VOCs emitted measured. Combustion tests were conducted according to the NES 713 method which is similar to the ASTM E662 and NBS Smoke Density methods. In these tests, a flame is impinged on a 3inch by 3inch square sample with any resulting combustion gases collected for analysis in Drager tubes. Gas traces are measured (ppm) and compared using a relative concentration coefficient (Cf) scale. The toxicity index is meaningful only under the precise conditions of the test and will vary, eg in higher oxidising flame conditions or according to flame temperature.
The performance of two tapes from Scapa's Autolon range is compared below with a traditional PVC tape. The results indicate clearly the benefits of using an Autolon tape compared with a PVC product in the same application. Toxicity from hydrogen chloride - the most aggressive and dangerous gas in incineration - drops dramatically to zero.
Ongoing research into new materials and technologies which enable the manufacture of zero halogen tapes is assisting the automotive industry as it strives to make ever more components recyclable. With pressure groups and governments increasingly placing recyclability on the agenda, manufacturers are keen to review alternatives but still need to keep a watchful eye on costs.
Based on the first halogen-free, fire retardant, low smoke and fume compounds, Autolon tapes are opening the route to meet proposed legislation cost-effectively.

Christine Toussaint is with the Automotive Business Unit, Scapa, Bellegarde, France. www.scapaautomotive.com