I remember scanning the first few pages of this book while browsing in a bookstore more than 20 years ago. All I can remember us that everything plastic was eaten or transformed by a rapidly spreading microorganism, and that an automobile engine stopped running and the passengers popped the hood and saw all the plastic components either made useless or disappear.
Is this Ill Wind (1995) by Kevin J. Anderson...?
It's the largest oil spill in history: a crashed supertanker in San Francisco Bay. Desperate to avert environmental damage—and a PR disaster—the multinational oil company releases an untested "designer microbe" to break up the spill.
An "oil-eating" microbe, designed to consume anything made of petrocarbons: oil, gasoline, synthetic fabrics, and of course plastic.
What the company doesn't realize is that their microbe propagates through the air. But when every car in the Bay Area turns up with an empty gas tank, they begin to suspect something is terribly wrong.
And when, in just a few days, every piece of plastic in the world has dissolved, it's too late...
From Kirkus Reviews:
A big, near-future disaster novel straddling the border between science fiction and technothriller, likely to appeal to fans of both. Anderson and Beason (coauthors of Assemblers of Infinity, 1993) begin with a huge oil spill in San Francisco Bay. The oil company decides to deploy an octane-eating bacteria, crossbred from two naturally occurring species, but the cure turns out to be worse than the disease: While scientists who bred the new bug swear it cannot spread beyond the spill, it contaminates gasoline in the tanks of cars crossing Golden Gate Bridge during the spraying. As each of the cars gasses up, the bacteria spreads to the gas in the service station tank. Worse, the bug soon develops an appetite for petroleum byproducts, in particular plastic and other synthetics. As the elaborate web of modern technology begins to disintegrate, the characters, a varied cast from all walks of life, are thrown back on their own resources for survival. A venial Louisiana congressman suddenly inherits the presidency; an insurance agent quits her job and takes to the wilderness; ghetto families from Oakland join forces with a hippie commune near Altamont; and a scientist developing a solar power facility in the New Mexico desert becomes the hope for technology's revival. Meanwhile, civilization degenerates into anarchy and cannibalism, the government attempts to retain control by increasingly harsh measures, and a good many protagonists die—usually nastily. In the end, there is hope, as the good guys manage to hang on in spite of all the forces ranked against them. Style and characterization are often clunky, but the fast- moving story pushes all the right emotional buttons for mass success: It's almost un-put-downable.
"Mutant 59: The Plastic Eater" Kit Pedler & Gerry Davis (1971) ?
Review from Amazon site:
Based on the classic sci-fi series Doomwatch, Mutant 59 imagines one of the most terrifying tragedies that modern science could create, a chilling and topical story of what happens when scientific research goes wrong and spreads terror through London (and endangers the world). When an airplane crashes the Ministry of Transport investigates, what caused it to fall out of the sky and could it happen again? Slowly they discover that science has unleashed a genetically engineered bacteria that feeds on (and destroys) all plastic materials. No-one takes any notice of the material used to build gas pipes, electrical insulation, cars and planes until it begins to disintegrate and explode. Has science created a biological time bomb? A jet plane crashes near Heathrow, in the Atlantic a nuclear submarine disappears without trace, central London grinds to a halt. As power stations explode and London's population is evacuated Anna Kramer and Luke Gerrard search for the scientific key to a fiery holocaust that is capable of infecting the world.
As per one of the answers to Trilogy: End of civilization by hydrocarbon-eating bacteria, a partial match is one of the books of the Daybreak trilogy which center around society trying to recover after a plastic/hydrocarbon eating bacteria is released. Not matching is that it's too recent (the first book was released in 2011), and the bacteria eats not only plastic, but also rubber, and there are nanites that ruin circuitry.
The near future. Heather O'Grainn is a worker in the Office of Future Threat Assessment in Washington state. Aa variety of groups with diverse aims, but an overlapping desire to end modern technological society (which they call the Big System), create a nanotech plague ("Daybreak") which both destroys petroleum-based fuels, rubber and plastics and eats away any metal conductors carrying electricity. An open question in the book is whether these groups, and their shared motivations, are coordinated by some conscious actor, or whether they are an emergent property / meme that attained a critical mass.
The Daybreak plague strikes, and world governments are helpless to deal with it. Industrial civilization rapidly breaks down, and tens of millions die in the U.S. alone (the global death toll measures in the billions). There is a presidential succession crisis. Just as society in the U.S. seems to start stabilizing, previously placed pure fusion weapons detonate, destroying Washington, D.C. and Chicago. This is followed by additional pure fusion weapon strikes, which are determined to be weapons that are being created on the Moon by nanotech replicators. A shadowy neofeudalist group (the "Castle movement") led by a reactionary billionaire may be inadvertent saviors of society... or may have some deeper involvement in things.