Water "plasticizes" the cotton. A plasticizer is a chemical that dissolves into a plastic and lubricates its molecules so that they can move across one another more easily. Cotton is almost pure cellulose, a polymer consisting of sugar molecules linked together in long chains. Since sugar dissolves easily in water, water dissolves easily in cellulose. Even though cellulose scorches before it melts, it can be softened by heat and water. When you iron cotton pants, the steam dissolves into the cellulose molecules and allows the fabric to smooth out beautifully.

Paper consists mostly of cellulose, a natural polymer (i.e. plastic) built by stringing together thousands of individual sugar molecules into vast chains. Like the sugars from which it's constructed, cellulose's molecular pieces cling tightly to one another at room temperature and make it rather stiff and brittle. Moreover, cellulose's chains are so entangled with one another that it couldn't pull apart even if its molecular pieces didn't cling so tightly. These effects are why it's so hard to reshape cellulose and why wood or paper don't melt; they burn or decompose instead. In contrast, chicle -- the polymer in chewing gum -- can be reshaped easily at room temperature.

Even though pure cellulose can't be reshaped by melting, it can be softened with water and/or heat. Like ordinary sugar, cellulose is attracted to water and water molecules easily enter its chains. This water lubricates the chains so that the cellulose becomes somewhat pliable and heat increases that pliability. When you iron a damped cotton or linen shirt, both of which consist of cellulose fibers, you're taking advantage of that enhanced pliability to reshape the fabric.

But even when dry, fibrous materials such as paper, cotton, or linen have some pliability because thin fibers of even brittle materials can bend significantly without breaking. If you bend paper gently, its fibers will bend elastically and when you let the paper relax, it will return to its original shape.

However, if you bend the paper and keep it bent for a long time, the cellulose chains within the fibers will begin to move relative to one another and the fibers themselves will begin to move relative to other fibers. Although both of these motions can be facilitated by moisture and heat, time along can get the job done at room temperature. Over months or years in a tightly rolled shape, a sheet of paper will rearrange its cellulose fibers until it adopts the rolled shape as its own. When you then remove the paper from its constraints, it won't spontaneously flatten out. You'll have to reshape it again with time, moisture, and/or heat. If you press it in a heavy book for another long period, it'll adopt a flat shape again.

Paper towels are made out of finely divided fibers of cellulose, the principal structural chemical in cotton, wood, and most other plants. Cotton is actually a polymer, which like any other plastic is a giant molecule consisting of many small molecules linked together in an enormous chain or treelike structure. The small molecules or "monomers" that make up cellulose are sugar molecules. We can't get any nutritional value out of cellulose because we don't have the enzymes necessary to split the sugars apart. Cows, on the other hand, have microorganisms in their stomachs that produce the necessary enzymes and allow the cows to digest cellulose.

Despite the fact that cellulose isn't as tasty as sugar, it does have one important thing in common with sugar: both chemicals cling tightly to water molecules. The presence of many hydroxyl groups (-OH) on the sugar and cellulose molecules allow them to form relatively strong bonds with water molecules (HOH). This clinginess makes normal sugar very soluble in water and makes water very soluble in cellulose fibers. When you dip your paper towel in water, the water molecules rush into the towel to bind to the cellulose fibers and the towel absorbs water.

Incidentally, this wonderful solubility of water in cellulose is also what causes shrinkage and wrinkling in cotton clothing when you launder it. The cotton draws in water so effectively that the cotton fibers swell considerably when wet and this swelling reshapes the garment. Hot drying chases the water out of the fibers quickly and the forces between water and cellulose molecules tend to compress the fibers as they dry. The clothes shrink and wrinkle in the process.

It is science. The needle is able to enter latex without tearing it because the latex molecules are stretching out of the way of the needle without breaking. Like all polymers (plastics), latex consists of very large molecules. In latex, these molecules are basically long chains of atoms that are permanently linked to one another at various points along their lengths. You can picture a huge pile of spaghetti with each pasta strand representing one latex molecule. Now picture little links connecting pairs of these strands at random, so that when you try to pick up one strand, all the other strands come with it. That's the way latex looks microscopically. You can't pull the strands of latex apart because they are all linked together. But you can push a spoon between the strands.

That is what happens when you carefully weave a needle into a latex balloon--the needle separates the polymer strands locally, but doesn't actually pull them apart or break them. Since breaking the latex molecules will probably cause the balloon to tear and burst, you have to be very patient and use a very sharp needle. I usually oil the needle before I do this and I don't try to insert the needle in the most highly stressed parts of the balloon. The regions near the tip of the balloon and near where it is filled are the least stressed and thus the easiest to pierce successfully with a needle. A reader has informed me that coating the needle with Vasoline is particularly helpful.

One final note: a reader pointed out that it is also possible to put a needle through a balloon with the help of a small piece of adhesive tape. If you put the tape on a patch of the inflated balloon, it will prevent the balloon from ripping when you pierce the balloon right through the tape. This "cheaters" approach is more reliable than trying to thread the needle between the latex molecules, but it's less satisfying as well. But it does point out the fact that a balloon bursts because of tearing and that if you prevent the balloon from tearing, you can pierce it as much as you like.

The main structural component of wood is cellulose, a polymer (plastic) consisting of long molecular chains of sugars. While cellulose is extremely useful and is by far the most common polymer/plastic in the world, it can't be melted because the temperature at which its molecular chains begin to move relative to one another is above the temperature at which those molecular chains begin to fall apart. In short, cellulose decomposes before it melts. Shaping or reshaping cellulose is very difficult, though chemical processes have made it possible to reform cellulose into such materials as cellophane and rayon.

The process you describe, bending wood while heating the wood with steam, takes advantage of the fact that cellulose molecules bind strongly to water molecules and that the water molecules then lubricate the chains so that they can move relative to one another. Water is said to be a "plasticizer" for cellulose. Heat, water, and stress allow the cellulose chains to slide slowly across one another. With enough patience, the wood's internal structure can be changed forever. When the heat, water, and stress are then removed, the wood keeps its new shape.

The easiest way to mold plastics is to form them directly inside a mold. Most plastics are made by attaching small molecules to one another in a process called polymerization. You begin with one or more small molecules or "monomers" and cause them to link together into in a "polymer." You can initiate this polymerization with chemical catalysts, light, or even heat. There are many plastic-forming systems that you can buy commercially. You simply mix a few chemicals together, pour the mixture into a mold and wait. Once the polymerization has finished, you have a molded piece of plastic.

If you don't want to do the polymerization yourself, you can start with a finished plastic and melt it. Most plastics that haven't been vulcanized into one giant molecule (as is done in rubber tires) will melt at high enough temperatures (although some burn or decompose before they melt). These molten plastics can be stretched, squeezed, or poured into molds to make just about any shape you like.

While I'm not up to date on actual studies, I would think that most food storage plastics introduce very little contamination into the foods stored in them. We have become so concerned as a society about toxic chemicals in recent years that we tend to overreact much of the time. While the actual polymer molecules in most plastics are relatively inert and harmless, plastics inevitably contain some small molecules, either by accident or by design, that work their way into food. Even if some of these molecules are toxic or carcinogenic, the quantities involved are almost certainly insignificant. Modern chemical testing can detect incredibly small quantities of various chemicals and we panic every time we find them in our environment. But the societal cost of banning or avoiding all contact with or use of these chemicals may have hidden costs that are worse than the problem we're trying to solve. Moreover, I'll bet that many of the foods put in plastic containers are greater health hazards than the containers themselves.

When the parachuter opens the parachute and begins to slow down, the parachute's nylon shrouds briefly exert a large upward force on the parachuter. Over a period of a few seconds, the parachuter slows from a downward speed of about 150 mph to a downward speed of 20 mph and experiences several g's of upward acceleration. To cause this much upward acceleration, the nylon shrouds must exert an upward force on the parachuter that is several times the parachuter's weight. The nylon shrouds are quite strong and can easily tolerate this much tension without exceeding their elastic limits. There should be no adverse effects on their elasticities.

There are two broad classes of plastics: (1) thermoplastics that can melt, at least in principle, and (2) thermosets that can't melt under any circumstances. Thermoplastics consist of very long but separable molecules and common thermoplastics include polyethylene (milk containers), polystyrene (Styrofoam cups), Nylon (hosiery), and cellulose (cotton and wood fiber). Thermosets consist of very long molecules that have been permanently cross-linked to one another to form one giant molecule. Common thermosets include cross-linked alpha-helix protein (hair) and vulcanized rubber (car tires).

Most common plastic items are made from thermoplastics because these meltable plastics can reshaped easily. But different thermoplastics melt at different temperatures, depending on how strongly their long molecules cling to one another. The plastic in an Oven Cooking Bag is almost certainly a thermoplastic form of Nylon, but one that melts at such a high temperature that it doesn't change shape in the oven. It's possible that the Nylon has been cross-linked to form a thermoset, so that it can't melt at all, but I wouldn't expect this to be the case.

These paints consisted principally of a pigment and a drying oil binder. The pigment was usually a colored powder that didn't dissolve in the oil. Historically, these pigments were materials collected from nature. The drying oil binder was usually linseed oil, obtained from the seed of the flax plant and a byproduct of the linen industry. Like most organic oils, linseed oil is a triglyceride--it consists of a glycerin molecule with three fatty acid chains attached to it. But while in typical animal or tropical plant oils the carbon atom chains of the fatty acids are completely decorated with hydrogen atoms (saturated fats) or almost completely decorated (monounsaturated fats), the carbon atom chains in linseed oil are missing a significant number of hydrogen atoms (polyunsaturated fats). The polyunsaturated character of linseed oil makes it vulnerable to a chemical reaction in which the chains stick permanently to one another--a reaction call polymerization. With time and exposure to air, the molecules in linseed oil bind together forever to form a real plastic! This "drying" process takes weeks, months, or years, depending on the chemicals present in the paint. It can be accelerated by the addition of catalysts--chemicals that assist the polymerization process but that don't become part of the final molecular structure of the plastic.

A gas permeable contact lens is one that allows oxygen to diffuse through it to the cornea of the wear's eye. While conventional hard lenses were made almost entirely of a plastic known as poly(methyl methacrylate) or PMMA, commonly known as Plexiglas or Lucite, gas permeable hard or semirigid lenses are copolymers containing both methacrylate and siloxane molecular units. The polymers used in soft lenses are made only of siloxane molecular units and are commonly known as silicon rubbers. The molecules in silicon rubbers are mobile at remarkably low temperatures, giving silicon rubber its flexibility. In fact, these molecules are so mobile that they must be linked together or "vulcanized" to keep them from flowing as a liquid at room temperature. Even when they have been linked together, portions of these molecules are very mobile, so that gas atoms and molecules can diffuse easily through them. I'm not sure what chemicals are used to color contact lenses, but I expect that the dye molecules are permanently linked to the polymer molecules to keep them in place.

While I don't know exactly what chemicals are used in hairspray, the main constituents are almost certainly polymer molecules--otherwise known as plastics. In the container, these polymer molecules are dissolved in a volatile solvent such as an alcohol or water, and pressurized with a chemical such as propane or a hydrofluorocarbon. When you spray the mixture onto your hair, the solvent evaporates and leaves the polymer molecules clinging to the hairs. These molecules are very long chains of atoms that form a stiff web around each hair and stiffen it. In general, the characteristics of polymers change with temperature and chemical environment. The polymer used in hairspray should be in the "glassy" regime, meaning that its atoms and molecules are essentially immobile at room temperature. Once the solvent is gone, the web of polymer molecules on the hairs is stiff and keeps the hairs from changing shape. Before you panic at the idea of spraying plastic onto your hair, consider that starch is also a polymer, as is hair itself. So putting hairspray on your hair is no different from putting starch on clothes.

Styrofoam is a rigid foam consisting of gas trapped in the closed bubbles of polystyrene. Polystyrene itself is a clear plastic that's used in many disposable food containers. It's a stiff, amorphous solid at temperatures below 100° C, where amorphous means that it has none of the long-range order associated with crystalline solids. The long, chain-like polystyrene molecules are arranged like a tangled bowl of spaghetti noodles. Amorphous plastics tend to be clear because they're very homogeneous (uniform) internally and let light passes through them without being deflected or reflected. Plastics that are partially crystalline tend to be white. I think that items bearing the #5 recycling label are made of polystyrene.

But when air or another gas is injected into melted polystyrene and the mixture is beaten to a froth, it forms a stiff white solid when it cools. The whiteness comes about because of inhomogenieties--the gas spoils the uniformity of the plastic so that light is deflected and reflected as it passes through the material. The Styrofoam retains the rigidity of the polystyrene plastic below 100° C, so that it's suitable for beverage containers for liquids that are no hotter than boiling water. At one time, one of the gases used to make polystyrene foams was Freon, but I believe that Freon is no longer used for this purpose.

Powder coating is done by combining the components of the coating (the binder--a polymer having giant chain-like molecules, the pigments, and the additives) to form a uniform solid, which is then pulverized to a dry powder and sprayed onto the surface to be coated. This coating is then baked to form a continuous film. There are two main classes of powder coatings: thermosetting and thermoplastic coatings. In a thermosetting film, crosslinking occurs between the molecules in the powder during baking. This crosslinking turns the baked film into a single giant molecule that can't melt or flow. In a thermoplastic film, thermal energy makes the binder molecules mobile enough to become entangled so that a continuous film forms and this film hardens upon cooling. While a thermoplastic film can still melt or flow, it can do that only at elevated temperatures. The powders are often given electric charges during spraying so that electrostatic forces will hold them in place until they're baked on.

The molecules of pectin contain enormous chains of atoms, often hundreds or even thousands of atoms long.. Such chains are also found in cellulose and starch, and are used by plants to give them strength and structure. These chain-like molecules are naturally occurring polymers or plastics. The giant molecules in pectin are based on small molecular units of D-galacturonic acid that have joined together like strings of paper dolls. The presence of acid groups on the pectin molecules help to make pectins very water soluble and also sensitive to the acid-base balance of their environment. I am not an expert in the exact structure and chemistry of pectin, or in the proper pH needed for jellymaking, so I can't give you an exact explanation for how to control the jelling process with acids. But the jell forms because these giant molecules spread out in the viscous solution of sugar and fruit juice, and form a tangled network of filaments that span the entire container. At high temperatures, there is enough mobility in the molecular chains to allow the mixture to flow, but at room temperature, the tangle of molecular filaments prevents flow. In the language of polymer or plastic science, the mixture goes from a liquid flow regime at high temperature to an elastic plateau regime at low temperature. When you deform cold jelly, you are pulling the filaments tight but they can't disentangle themselves enough to allow the jelly to actually flow. When you deform the cold jelly too far, the filaments begin to break and the jelly tears into fragments. However, when you warm the jelly, thermal energy allows the filaments to move past one another and the jelly begins to flow like a thick (or viscous) liquid.

Different plastics are handled differently for recycling. Thermosets, such as rubber in tires, cannot be melted and cannot be recycled. Only thermoplastics can be melted for true reuse. There are 6 common thermoplastics that are recycled. These are numbered 1 through 6 on their bottoms. Objects made from one of these plastics can be collected together, melted, and then reformed into new useful objects. Unfortunately, the melted and reformed plastic isn't as pure as the original. The plastics manufacturers would rather clean up petroleum into petrochemicals and then make pure plastics than start with plastic objects, clean them, and reuse them. Because the recycler can't control what was in the plastic objects, these objects cannot be used for critical applications such as food containers or plumbing. Thus most recycled plastic is used for less profitable applications. If the recycler could be absolutely sure that the plastic hadn't been contaminated, some of it could be reused very easily. Plastic milk jugs could be reformed into plastic milk jugs over and over again.

Some glues literally "dry," since they contain a plasticizer chemical that evaporates to leave a firmer plastic. Other glues polymerize directly during the gluing process. For the glues that dry by evaporating plasticizer, the choice of plasticizer is critical. Water leaves relatively slowly compared to volatile organic solvents such as toluene or acetone. That is why water-based white glue dries more slowly than organic-based plastic cement. But the glues that polymerize during the gluing process (they "cure" rather than "dry") have a broad range of speeds. Some of those glues polymerize very rapidly (e.g. superglues and 3-minute epoxies) and some go much slower (normal epoxies). In general, slower glues produce stronger materials because they contain long polymer molecules. The fast curing glues form too many short polymer molecules and are not as tough.

I don't know for sure, but I suspect that they are plasticized materials (polymer molecules and softening chemicals) in which either the polymer molecule or the plasticizer or both are explosives. Actually, I just looked it up and found that it is based on RDX (a nitrated form of hexamethylenetetramine). The RDX is mixed with oils, waxes, and plasticizers to make a stiff putty. That being the case, it isn't really based on polymer molecules so that the name "plastic" refers more to its ability to assume different shapes at will.

Covalent bonds are very strong and very directional (meaning that they tend to arrange the atoms at specific angles with respect to one another). Once a molecule has formed, the covalent bonds usually prevent it from rearranging at all but the highest temperatures. Much of the field of organic chemistry is devoted to the problems of controlling the formation of covalent bonds. Very subtle reactions are used to replace one atom with another or with a specific group of atoms. The only real control that the organic chemist has is energetics, dynamics, and statistics. By energetics, I mean that objects tend to follow paths that reduce their potential energies as quickly as possible so that molecules will undergo reactions that reduce the overall potential energies as quickly as possible. If you chose the right chemicals, you can use this energetic control to determine the final molecules. By dynamics, I mean that the reaction pathways are also influenced by issues of motion (inertia, momentum, etc.) so that some energetically favorable reactions may not form because inertia and momentum makes it hard for them to occur. By statistics, I mean that reactions that increase the order of the molecules tend to be rather rare. Nature is always becoming more disordered so that a reaction that brings more order to the universe is unlikely to occur. When you mix chemicals together, they are unlikely to react to form a complete Faberge Egg, complete with a miniature winter scene inside. These different reaction issues can be used together or separately to manipulate atoms into a specific molecule. Usually some of the molecules produced in a synthesis are imperfect and must be separated from the desired molecules. So most organic synthesis projects involve many reaction and purification steps.

Probably. HDPE (high density polyethylene) allows blue and ultraviolet light to strike the milk, degrading some of its nutrient molecules. It isn't radiation from the plastic but rather the sunlight that the plastic doesn't keep out of the milk. Adding an absorbing chemical to the plastic would help, but it would create an amber plastic (like amber medicine bottles; which are colored for this same reasons). If we could get used to having amber plastic, we would probably be better off. However, people seem to tolerate amber orange juice jugs but not amber milk jugs.

Yes. Vulcanization is done with the object in its final form. The plastic is assembled while it is still thermoplastic; without the cross-links that render it unmeltable. It is then vulcanized into a single giant molecule; a thermoset. This vulcanization may be done with sulfur, as in car tires, or it may be some other reaction. In silicone rubber (e.g. bathtub chalking), the vulcanization occurs spontaneously in air. The polydimethyl siloxane molecules are treated at their ends so that they vulcanize in air, releasing acetic acid (the vinegar smell). The resulting thermoset silicone rubber is one giant molecule and cannot melt any more.

Working with Teflon is difficult in any case. The molecular chains are extremely long, typically 100,000 carbon atoms long. It does not melt easily (it is used for high temperature applications) and is a very viscous liquid even when it does melt. Teflon is attached to surfaces by sintering it from a powder. At a high enough temperature, the molecular chains begin to move about somewhat so that they bind together into a continuous material. They also enter pores and crevices in the surface and becomes wedged inside when it cools. With enough of its chains extending into the pan surface, the whole Teflon sheet is permanently attached to the pan.

A racquetball is made of vulcanized rubber. Rubber consists of countless molecules, each one of which is principally a long chain of carbon atoms, decorated with hydrogen and other atoms. It resembles of bowl of tiny spaghetti strands though each rubber molecule is much, much longer than it is thick. But simple rubber melts rather easily and becomes gooey when warm. To make it more durable, it must be vulcanized. During vulcanization, the individual rubber molecules are cross-linked to form a permanent network of coupled strands. They can't move relative to one another, which is why the racquetball can't melt. It can only burn when you heat it. So the whole racquetball is one giant molecule. If you cut it in half, you are slicing the molecule in half. It doesn't crumble, it just has many of its bonds broken. That's not a problem because bonds break and remake all the time in the molecules around us.

Since a tire cannot be melted, it can't simply be reformed into a new tire. Moreover, it contains lots of belting materials that would have to be removed and reinstalled in the new tire. So the only recycling technique available for tires is to replace the tread itself. They shave away the outside of the tire to remove any remaining tread (working carefully, so as not to damage the belts), and glue a new layer of unvulcanized rubber onto the outside of the tire. The tire is then placed in a mold and heated. This heating causes a chemical reaction known as vulcanization to occur in the new tread rubber. This vulcanization bonds all the rubber molecules together and also binds them to the original tire. If done correctly, the entire tire, old and new, becomes a single gigantic molecule and the chances of losing the tread while driving should be minimal. Furthermore, the mold forms a tread on the surface of the new rubber so that the tire is structurally very much like a new tire. However, poor retreading work or accumulated damage due to many retreading operations can produce a weak tire and allow the tread to tear away from the tire body. This separation usually occurs while the tire is spinning rapidly and the tension forces within the tire are maximized. Such separation accounts for the huge strips of tread material you often see on highways.

Ideally, the glue would form strong covalent bonds with the material and then form countless strong bridges from one object to another. Unfortunately, getting the glue to form such strong bonds with a surface is rarely possible. Instead, the glue forms weaker hydrogen bonds or van der Waals with the surface and is not so firmly attached. The glue's polymer molecules may also extend into the surface, in cracks and fissures to form a more sturdy attachment. Clearly, surface preparation can help the gluing process. Glue will bind more effectively to a porous, rough surface than to a very smooth, impermeable one.

When two atoms form a covalent bond, their total energy is reduced by their proximity. It thus takes energy to separate them. If that energy isn't available, they will cling to one another indefinitely. The two ways in which they lower their total energy by being close are (1) electrostatic attraction and repulsion and (2) lower kinetic energy. Two atoms experience both attractive and repulsive forces as they approach one another. Their positively charged nuclei repel one another, their negatively charged electrons repel one another, but their nuclei attract their electrons. The nuclei never get very close and the electrons manage to stay relatively far apart, too. The dominant effect is an attraction between the electrons and the two nuclei. The result is a net attraction. The nearby atoms are pulled toward one another by these electric forces. The lower kinetic energy comes about because of quantum effects. The electrons travel about the nuclei as waves. When the atoms are far apart, the electrons must orbit their individual atoms. Because they are then confined to small domains, they must have short wavelengths. These waves must be short enough to fit properly into their small confines. Short wavelength objects have high kinetic energies (e.g. short wavelength light is x-rays and gamma rays). But when the atoms are touching, the electrons can spread out between both atoms. Their wavelengths increase and their kinetic energies diminish. These two effects (lowered electrostatic potential energy and lowered kinetic energy) reduce the total energy when the two atoms touch. The result is the covalent bond.