Chemical Reactions Between Parts

[Miatatom]

I recently bought a Revell Ford Mustang GTO IMSA racer with the Motorcraft decals off of eBay. This kit had been opened previously. When I received it, I checked everything over and discovered something that I found very unusual. One of the tires was stuck to some of the clear plastic parts (windshield, rear window and one taillight lens). They had imprints in them of the tire including the lettering. Has anyone ever heard of anything like this before? Should precautions be taken to ensure that dissimilar materials like this are separated, especially if kits will be stored for a while? The seller was nice enough to give me a full refund.

Edited February 10, 2014 by Miatatom

[MsDano85gt]

I have had that happen before on some older mpc model kits want to say theres some chemical within the rubbers from the tires that has a reaction to regular plastic parts..... that is perhaps why nowadays they usually have tires seperated in their own plastic bags in the kit boxes..... i may be wrong tho or therer might be technical jargin for this epedemic but you are not alone in this matter

[o-man]

I've had the same thing happen before. Thankfully, I was able to polish most of marks out.

[Erik Smith]

It's very common - older kits especially. I always separate tires from all the plastic.

[JohnU]

This is why I always open older sealed kit when I buy them! Some collectors will cringe at the idea claiming it kills the value. But I would rather know that the contents are usable, undamaged and complete than sit on a sealed box of garbage!

[disabled modeler]

I have had that happen too...also with some clear display cases and the tires.

[Ace-Garageguy]

This is very common with some older kits. I've seen it in Revell, AMT, Johan and MPC from the 1960s mostly. Although I haven't researched the exact chemical reaction, it has to do with the plasticizers in the vinyl tires (which keep them flexible) leaching into the styrene they're in contact with, and acting as a slow-working solvent that allows the styrene to locally soften and 'flow'.

It's also a problem between mounted tires on styrene wheels on older models, and can be controlled by wrapping a wheel with one layer of BMF before mounting the tire.

I've had some older models significantly damaged, in sealed boxes, and I've seen wheels turned to rubbery goo over time when in contact with vinyl tires.

Here's a thread on another forum...http://www.scalemotorcars.com/forum/large-scale-motorcycle/2179-plastic-vinyl-time.html

[Art Anderson]

This is very common with some older kits. I've seen it in Revell, AMT, Johan and MPC from the 1960s mostly. Although I haven't researched the exact chemical reaction, it has to do with the plasticizers in the vinyl tires (which keep them flexible) leaching into the styrene they're in contact with, and acting as a slow-working solvent that allows the styrene to locally soften and 'flow'.

It's also a problem between mounted tires on styrene wheels on older models, and can be controlled by wrapping a wheel with one layer of BMF before mounting the tire.

I've had some older models significantly damaged, in sealed boxes, and I've seen wheels turned to rubbery goo over time when in contact with vinyl tires.

Here's a thread on another forum...http://www.scalemotorcars.com/forum/large-scale-motorcycle/2179-plastic-vinyl-time.html

That's the result of older PVC (vinyl) tires and styrene plastic. A bit of my history here:

In February 1976, I took a position as the Human Resources Director (Personnel it was called back then) at an Essex Wire Division of United Technologies Wire Assembly Plant here in Lafayette (we built the dashboard wiring harnesses for the old large Thunderbird and Lincoln Continental Mk IV and Mk V along with taillight harnesses for Pintos and Mustangs at the time). In early 1974, OSHA declared PVC Monomer (the plasticizer chemical that makes normally hard vinyl soft and rubber-like) to be carcinogenic, which was a real hazard, as the PVC pellets we were using contained a lot of the stuff, and it gassed out when melted in the injection-molders used to mold PVC plugs onto the ends of wiring harness subassemblies. A major part of my job there was to keep our workers informed of the hazard, and what had been done to eliminate it from our factories--and advise new employees coming on as to the problem as well--so I necessarily had to become well-informed on the subject. Fortunately for all concerned, the chemical and plastics industry came up with a very acceptable method of recapturing the excess monomer gas in the manufacturing process for PVC feed stock pellets, and the hazardous out-gassing quickly became a non-issue. This was the same time-frame when the once-dreaded "Revell Tire Disease" was a constant headache for modelers--Revell's tires would literally dissolve the rims of model car wheels, sometimes in a matter of a few months after assembly, but all the other model kit manufacturers suffered the same problem to at least some degree. Revell and AMT both "solved" the problem by going to two-piece hard polypropylene plastic for their tires (which still are found in old kits from that time frame, BTW, and some reissued kits were using those as late as the early 1990's. The recapturing technology very much eliminated the carcinogenic hazard to workers in factories, and as a further benefit, tended to greatly reduce the possibility of the monomer from being concentrated enough in our 1/25 scale model tires so as to cause serious "leaching" of that stuff out and into the surface of styrene plastic--which pretty much ended the problem as long as the OSHA regulations were followed carefully.

While the problem went away pretty much as we US modelers are concerned, it's still a periodic problem with Chinese manufacturers, as apparently the regulatory process in China (and probably other 3rd world Pacific Rim countries as well where environmental and occupational hazard regulations are much more lax and often are not seriously obeyed at some point in manufacturing processes) when a feedstock manufacturer slips in old-formula PVC pellets to their customers (the factories who make the model car kits over there that we like to build). Thus, the periodic problem crops up in some plastic kits every so often (and raises management's blood pressure exponentially!), even though a PVC-Monomer free plastic formula is clearly specified.

The old-formula PVC monomer tends to leach out of the tires of those older kits (sometimes to the point of leaving an oily-appearing film on them!) and if it contacts styrene plastic parts, even decals and even the prepainted surfaces of a prepainted kit, and the offending tire simply puts its imprint on those parts, as the monomer softens styrene and paint every bit as well as it does hard PVC. (Incidently, do not wrap model kit parts in Saran or other clear "Cling" food wrap--that stuff is soft PVC made with PVC Monomer, and it WILL attack styrene and painted surfaces--such as clear-coated chrome parts trees!).

As Bill Engwer stated, the best protection against having a vinyl tire "eat" into a styrene wheel is to wrap a band of Bare Metal Foil around the rim before you mount the tire on it. Any metal is a perfect barrier against the possibility of PVC Monomer still being present in the tires in enough concentration to seriously damage the rims. Also, when buying an older model kit (lots of those kits from the 60's and early 70's out there on vendors' tables at model car shows!), take the time to put the tires in a small Ziploc bag (Ziploc bags are made from polyethylene plastic, and are very resistant to PVC monomer--I've never had a problem with any tires I've packaged thus, even though the plastic bag itself inevitably will touch, lay right up against, the styrene plastic parts in the kit box.

A perplexing problem with a very simple solution.

Art

Edited February 10, 2014 by Art Anderson

[Miatatom]

Thanks for the extensive and thorough explanation, Art.

I have to agree with JohnU as well. I don't have too many sealed kits but I'm going to be going through them all to ensure I don't have the same problem with other kits.