Guest Column: 6ppd conundrum may benefit from historical perspective

Industry activities related to addressing a lawsuit and environmental allegation against the use of N-1,3-Dimethylbutyl-N phenyl-p-phenylene diamine (6ppd) as an oxygen/ozone antidegradent can benefit from a historical review of antiozonants that go back to the mid-1950s when Universal Oil Products offered their new experimental UOP88 (a liquid dioctyl ppd). It was an oily liquid, hard to handle and required compound and manufacturing adjustments.

This was the start of the ppd antiozonant family evolution which is now at the 6ppd stage.

In the '50s, we were dealing with serious groove cracking on 4-ply nylon casings with none of the chemical, manufacturing and design tools we now have. The current search for a chemical that can be an easy drop-in replacement for 6ppd may be successful, but we have to quantify the time line for the no-risk substitution a tire requires.

In my direct compounding experiences with replacements, R&D is littered with a range of "be careful" experiences, which include compound processing and manufacturing anomalies, warehouse appliance surprises (purple-stained refrigerators), vehicle airborne trunk stain issues, vehicle odor issues and certainly very important worker health issues.

In other words, we must be very careful and not push an accelerated time line on a chemical replacement unless there is plenty of real world experience behind it.

Tires have a unique position in the automotive safety equation. Unlike every other critical part of a vehicle, tires operate in a chaotic environment including poor maintenance and just plain neglect. This interactive service environment requires long-term testing in the field.

It cannot be duplicated on a computer, in the laboratory, on a dynamometer or a limited fleet test.

Unlike the early days of antiozonants, we now have additional tools to help address the 6ppd allegations. They could offer low-risk, early-term (temporary?) solutions such as:

1. Reducing/replacing 6ppd in compounds subject to road particle abrasion and water leeching with ppds that offer more resistance to water extraction (i.e. such as diaryl ppds). It could mean using an internal (not exposed to the environment) 6ppd reservoir under-tread cushion to offer tread design grooves important crazing/crack resistance.
2. Replacing 6ppd in sidewall compounds that are subject to water leeching with a veneer of weather-resistant elastomers such as EPDM/halobutyl/NR. This may not be as easy as it sounds and will raise costs since it requires additional manufacturing steps and controls to assure adhesion and resist blemish blisters. This could offer the cosmetic advantage of tires remaining black without a discoloring surface blooming of antiozonants that then wash into the environment (particularly in the presence of ice melt chemicals).
3. Actively endorse high-purity, zero-moisture nitrogen inflation for improved inflation pressure retention, possible reduced dependency on certain antioxidative chemicals and improved tire pressure monitoring systems' (TPMS) reliability.

Herzlich is a retired tire industry veteran who served as technical editor for Rubber News for more than two decades and also was the founding conference chairman of the International Tire Exhibition & Conference.