Guide to Working with Plastics -- Man-made Materials: Many Uses

• Intro
• A Beginner’s Guide to Manipulated Molecules
• Where and How to Buy Stock
• Readying the Stock for Cutting or Drilling
• Familiar Cutting Tools, Unfamiliar Techniques
• Drilling and Counterboring
• Rigid Sheets and Tubes Made Pliant with Heat
• Giving Luster and Polish to Edges and Surfaces

6---

=== Squeeze play. An oven-softened strip of sheet acrylic is molded into an S shape by means of a wood block sawed into two matching parts. The C clamp will hold the two parts of the jig together until the plastic cools and hardens—a matter of minutes, All thermoplastics, of which acrylic is one, have this capacity to be shaped by a combination of gentle heat and pressure.

In 1863, a New York printer named John Wesley Hyatt set out to concoct a substitute for ivory, hoping to win a $10,000 prize offered by the American billiard-ball maker Phelan & Collender. Hyatt’s tinkerings yielded celluloid—too brittle, alas, to displace elephant tusks as the source of billiard balls, but perfect for ladies’ combs and gentlemen’s collars. Celluloid was the first of the plastics, a family of materials that now touch every aspect of our lives.

Once regarded as cheap substitutes for “real materials,” plastics today do a tremendous assortment of jobs better than any natural substance can. The layers in a sheet of plywood are bonded by plastic resins, the strongest of all adhesives. Gossamer-thin sheets of polyester film cover windows to form solar screens that block out 80 percent of the sun’s rays without interfering with the view. Tough, durable nylon has replaced metal in gears for many home appliances because the smooth, waxy texture of nylon gears allows them to turn quietly and efficiently without a drop of oil. Lightweight foamed plastics, sandwiched into concrete blocks and panels, serve to insulate the foundations and walls of a house.

Amazingly, almost all of these plastics and countless others are derived from one source—petroleum. Plastics are made by breaking down the components of crude oil into simple molecules made up of hydrogen and carbon atoms, then stringing these units into long molecular chains.

The unique and widely variable forms that plastics take, as well as their lightness, strength and malleability, result in part from the variety of molecules that can be derived from petroleum and in part from the different methods chemists have devised for linking them. To further increase the range of possibilities, chemists can change the characteristics of plastics with various additives. Just six years after John Hyatt created celluloid, camphor was added to that bone- hard plastic, rendering it resilient enough for use in billiard balls. Today, the addition of microscopic whiskers of boron to epoxy resins produces a material so strong that it’s used to make helicopter rotor blades.

Despite their chameleon qualities and their bewildering variety of characteristics, plastics are, on the whole, quite manageable materials. Many of the familiar tools and techniques that are employed in working with wood and metal can also be used to cut, file, shape, join and mold these synthetic substances. Indeed, plastics are so adaptable to the skills and needs of the amateur that, as sheathings, adhesives, coatings and moldable resins, they lend themselves to literally hundreds of small and large projects designed to improve and repair the home.

A Beginner’s Guide to Manipulated Molecules

Plastics, once scorned as cheap substitutes for natural materials, are now welcomed throughout the home for qualities that in mans cases make them superior to the materials they replace. Rigid plastics serve as patio roofs, plumbing pipes, lighting fixtures and furniture. Flexible varieties go into garden hoses, upholstery, dropcloths, and food and beverage containers. As tiny particles or liquid res ins, plastics are found in many paints, sealants, caulks and adhesives. Other res ins can be cast or molded into hard, durable doorknobs and tool handles, or they can be bubbled into rigid foams for insulation and insulated cups, or into supple ones for mattresses and pillows.

Despite plastics’ bewildering variety, each kind—as shown in the chart—offers a unique set of proper ties that can be used to advantage by the amateur. The most notable property is the one implied by their name: At some point in their manufacture, all plastics are truly plastic—either fully liquid or pliant enough to be formed and molded. They are organized into two distinct groups according to the circumstances under which they become plastic, or capable of being molded.

Plastics of the first group, the thermo setting plastics, moldable only once, after which they solidify through a chemical process. These plastics, familiar as epoxy cements and as the hardened resins used to surface such laminates as Formica, cannot be reheated to moldable softness; high temperatures merely char and decompose them. Those in the second group, the thermoplastics, regain their pliancy each time they are heated and can be remolded repeatedly. They are most familiar as the vinyls used in house siding and the polyethylene of food-storage bags, as well as the hard, glossy polypropylene plastics out of which appliance casings are molded and the clear, tough acrylic and polycarbonate of shatterproof windows.

Both kinds of plastic behavior are a boon to the amateur. Thermosetting plastics often come as liquid resins—epoxy and polyester are commonly available— that are easy to cast at room temperature. Mixed with hardener, they set to form hard and heat-resistant products ranging from a doorknob to a shower enclosure reinforced with glass fibers.

Solid thermoplastics, on the other hand, can be softened with moderate heat, then twisted, creased or bent. A seemingly rigid sheet of acrylic glass, for instance, can be softened in a kitchen oven to make fittings and furniture parts that are both decorative and practical.

Working with plastics involves many of the same shaping and finishing operations used in metalworking and wood working. Thermoplastics parallel metals in that they can be heated for bending and can be welded. Like wood, plastics can be cut with hand and power saws, drilled, shaped with files and smoothed with sandpaper. These familiar processes, however, can sometimes take unfamiliar twists when they involve plastics. Many plastics, for example, soften at heats so moderate that the friction of a power saw, drill or sander may be enough to melt them and gum the tool. Other plastics are so flexible that they distort when sawed or drilled, making it difficult to do accurate work. The specific remedies for these problems are presented in the pages that follow.

In many instances, the unusual characteristics that present problems can also be turned to advantage. Exposed to strong cleaning solutions and solvents, for example, many plastics—including most of the thermoplastics and especially polystyrene—weaken, crack and soften. Although this means that painstaking care must be used in matching solvent- based glues and paints to the plastic surfaces, it also makes possible a unique bonding process called solvent cementing. A bead of solvent, run along the seam, softens the adjacent plastic surfaces. The edges then meld, and the bond hardens as the solvent evaporates.

Because they are fluid in some stage of their manufacture or use, plastics can be colored, combined with additives or reinforcements, or frothed into foams, all of which further broadens the range of their properties and applications. Additives that can be used at home include mineral fillers that make casting resins thicker and easier to work with, as well as coloring agents. And glass-reinforced polyester is easily fabricated at home by the layering of mats of glass fiber soaked with polyester resin.

= = = Basic Safety Rules for Working with Plastics = = =

Working with plastics requires many of the precautions that are standard in woodworking and metalworking. Guards on power tools and heating equipment should be checked and maintained. Safety glasses are a must, and a dust mask is essential for operations that produce powdery residues. In addition, plastics call for precautions against two special dangers: irritation from fumes and flammability.

With liquid plastics—the resins, hardeners, paints, sealants and adhesives— both hazards are immediate. While working with these liquids, ensure proper ventilation to disperse fumes. In many cases, you should wear a respirator with a charcoal filter. Don’t smoke, and never work near an open flame. Solid plastics may generate harmful vapors, too, if they are allowed to become overheated during welding or hot-bending operations.

To avoid skin contact with the liquids, wear rubber gloves and a shop apron while pouring or mixing. Proper clothing is also important for sanding, drilling and sawing reinforced plastics— especially those that include glass; tiny, razor-sharp particles are released during these operations and will quickly irritate skin, eyes and lungs. Gloves, a shop apron and a good-quality dust mask are essential.

Many solid plastics are somewhat flammable, although no solid plastic in common use today presents any greater fire hazard than wood. The fumes of burning plastics, however, can be toxic. Keep a multipurpose, dry chemical fire extinguisher nearby, especially if you are working with liquid plastics.

=== Plastics in the home. The left-hand column of the chart at left lists the plastic household objects most likely to confront someone engaged in home crafts. To the right are the plastics most of ten used for each object. In cases where a plastic is known by an abbreviation—ABS for acrylonitrile-butadiene-styrene, PVC for polyvinyl chloride and PVDC for polyvinylidene chloride are examples—the abbreviation is listed. Similarly, common names and widely recognized brand names are included in parentheses where helpful. In some cases, nearly identical objects are made of different kinds of plastic, de pending on the manufacturer. When repairing such objects, you can tell similar plastics apart by consulting the chart on page 12 and matching the plastic at hand to the one on the chart whose characteristics it most closely resembles.

--The Substances of Everyday Objects--