I’ve had three products where rubbery plastic used for grip got a lot softer over a period of years. One was on a set of tongs in which the plastic was just pressed into a metal frame. One was a coating applied to the handle of a corkscrew (“wine key” for snobs), and one was the rubberized coating on an emergency radio (very similar to, if not the same as, this one)
The grip on the tongs softened and fell apart. The grip on the corkscrew got softer and softer (and grosser and grosser to hold) until it was better to just scrape it off the hard plastic handle beneath the coating. The radio continues to live in the emergency supplies but it also feels gross to touch. Like warm, rubbery slime.
Use and storage of all three were different. The tongs were used and hand-washed regularly with dish soap (let’s say weekly) and stored in the kitchen cutlery drawer that’s opened many, many times in a day. The wine key was used regularly (probably once or twice a week) but never washed. It’s stored in a drawer that’s opened less frequently but probably almost every day. The emergency radio was stored in a sealed pouch deep in a tightly packed backpack and got, for all practical purposes, almost no exposure to air or sun. All stored in the same house as the same temperature.
So what gives? What causes this type of rubbery plastic to fail over time?
[No Discord, this is not similar to, “What causes the male body to get hairier the same time the head gets balder?”]
“Plastics” can be so many different things, but if it fell apart completely there was likely a breakdown of the original long chain polymers. This could have been because of inherent instability of the material or because of interaction with additives used to get the desired softness or color.
I have had this happen to several items, most often with something that has a “rubbery” grip(s). As with the OP different storage conditions between them.
The only thing I can guess is with this type of material (plastic?) some ingredient is off-gassing and when enough is released over the years it starts to degrade.
My wife had to throw away a favorite hair brush because of this.
The more common problem is plastics getting harder and more brittle over time. The results you see are usually a result of degradation of the plastic due to heat, UV light, or absorption of water. But other chemical processes may continue to affect the plastic over time, often described as depolymerization. I have seen it said that some soft plastics are infused with oils that they lose over time, not resulting in hardening of the plastic but causing it to fall apart.
Most plastics get harder and brittle over time because they can lose the plasticizers keeping them flexible. Volatile plasticizers are often used because they cost less.
Which article talks about how “Elevated temperatures and a closed environment usually accelerate depolymerization.” Well, closed environment certainly describes the radio. Elevated temperatures probably helps explain the tongs, which we likely used for deep frying a few times. Still no idea what killed the corkscrew other than simple inadequacy of the polymer used.
Thanks! I looked for a previous thread. I will read and learn.
I’ve had several tools and devices afflicted with the same issue.
If you’re not concerned with aesthetics, one way I’ve found to reduce the sticky-ness so that I can retain the use of said device is to rub talcum power onto/into the material, then wipe off the excess. It might look hazy, but it won’t be sticky anymore.
I’ve had something similar happen to shoe soles. Most spectaculary was a pair of hiking boots that I bought on sale about 20 years ago and stored in the closet unused. When I finally excavated them a few weeks ago, the composition soles disintegrated the minute I started walking.
What I hate are hand tools that have rubberized grips that get to a point where your hands are left black from the material breaking down into a very fine powder. For example, I have a set of pneumatic nailers (brad and finish) and you can’t touch them without your hand getting covered in hard to remove black. My solution is to put some thicker plastic bag (think tortilla bag) around and tape over that terrible grip. I’ve tried cleaning them with different solvents and nothing fixes this that I can find. Anyway have a better solution than basically wrapping them in a condom?
Just to be clear, I would not wrap the tape over a plastic bag layer, just wrap the self-amalgamating tape directly over the crumbling grip with some tension (the instructions say it should be stretched to twice its original length while applying) and overlapping the turns so as not to leave gaps (the edge of each new turn should come to the center of the previous turn)
I’ve wrapped so many bike handlebar grips, this will be second nature to me! Speaking of that, I need to do my road bike as well. Grip wrapping weekend!
“Plastics” is a broad term, but most of these polymeric materials degrade over time by a process of oxidation where the formation of free radicals is part of the process. Heat and UV light accelerate the process. Most of the polymers undergo chain scission and lose strength (get gummy), but some crosslink and can get brittle. Various “anti-oxidants” (i.e. hindered phenols) are usually added during processing to inhibit the formation of free radials and extend the shelf life. If the plastic (i.e. vinyl) contains a volatile plasticizer it can get brittle over time just from the lose of plasticizer.
Carbonyl bonds, that is, a carbon atom double bonded to oxygen (C = O) is most hydrolytically susceptible among commonly used medical plastics . The carbonyl bond could be attached to other atoms in the polymer such as oxygen and nitrogen and these bonds could be esters, amides, carbonates, and urethanes. Among carbonyl polymers, anhydrides display the highest hydrolysis rates followed, in order, by esters and carbonates. Other carbonyl groups such as urethane ), amide, and urea can normally demonstrate good long-term stability in vivo especially if the group is contained within a hydrophobic backbone or highly ordered morphological structure.
So the last bit about , hydrophobic backbone or highly ordered morphological structure … well hydrophobic means slippery and highly ordered morphological structure means it won’t return to shape if stretched. It makes it stiff or brittle, rather than stretchy. So PET, your plastic drink bottle is slippery AND unable to stretch much while able to return to shape.
Another solution which may work for some applications, is to cut off the rubber coating and re-apply a fresh rubber grip coating with something like Plasti Dip. It appears to be available in several colors. The interwebs tell me that objects may need to be recoated every 3+ years.
I don’t think your plastic is depolymerizing – that usually takes effort. What is more likely is that the individual strands of polymer are becoming less cohesive. what’s even likelier is that the plasticizer in your plastic is aging.
Think of your plastic like a huge plate of spaghetti afflicted with serious static cling. The static cling keeps the strands of spaghetti in close contact, but if things are hot enough they can easily slide over each other to fill the space they have, almost like a liquid. In just the same way, a plate of spaghetti can take the shape of the bowl they’re in, or the plate. Freeze it and they stay in that position. Each strand of spaghetti is a single polymer chain (most polymers are linear chains. we won’t worry about block polymers here). Thermoplastics act the above way.
Rubber, a natural polymer, acted that way. In hot wweather Macadamized fabrics (raincoats made by coating cloth with rubber) used to get runny. So did rubber boots. Until Charles Goodyear by a happy accident discovered vulcanizing. The sulfur he added caused crosslinks to develop between the polymer strands and 'locked them in place. Something similar happens when you add borax solution to polyvinyl alcohol (which is a collection of polymer chains that still act very much like a liquid. The borax causes cross-linking that makes the PVA more stodgy, so it acts like a jelly rather than a liquid. This is the stuff Nickelodeon “Slime” is made of. You can do the same thing with a solution of Elmer’s glue-all (which is polyvinyl acetate). Adding borax cross-links the polyvinyl acetate just like polyvinyl acid, and you get a jelly-like semisolid, although one that’s translucent rather than transparent. In most cases, though, cross-linking gives you a better, more solid “solid”, like vulcanized rubber.
In a lot of polymers you don’t even have to bother with cross-linking. Polyethylene (probably the most common plastic), especially High Density Polyethylene (HDPE) will pretty much stay in place unless you get it really hot. So with polyethylene terephthalate (PET, the stuff they make plastic water and soda bottles out of).
But say that you want your plastic to be softer and more resilient. In that case, people add substances called 'plasticizers". These go interstitially with the polymer strands, and the more you add, the softer things get. They also sometimes get tacky. This is how they make those window-stick jelly things.
Sometimes when such plasticized plastics get too old or too hot or both the plasticizer starts to bleed out, and you start to get a gummy mess, as you describe. I don’t know an easy solution to “de-gum” such plastics. Easier to throw it out and get a new piece
This happened to my Ooma phone device thing. When I called the company, they were quite familiar with it and told me to use acetone to remove the tackiness. It worked to some extent, but it’s still kind of tacky.
In the 2 years since I wrote that, the Ooma has maintained the same reduced level of tackiness. If it were a cheaper device, I’d just buy a new one.