Biopolymers

From GreenPlastics

	This article is just plain messy. Please help to clean it up and make it more organized. Remember to use headings in order to identify separate sections and automatically generate a table of contents.

This is the article describing biopolymers. To view a list of different types of biopolymers see Biopolymers (list).

Biopolymers are polymers that occur in nature. Carbohydrates and proteins, for example, are biopolymers. Many biopolymers are already being produced commercially on large scales, although they usually are not used for the production of plastics. Even if only a small percentage of the biopolymers already being produced were used in the production of plastics, it would significantly decrease our dependence on manufactured, non-renewable resources.

• cellulose is the most plentiful carbohydrate in the world; 40 percent of all organic matter is cellulose!
• starch is found in corn (maize), potatoes, wheat, tapioca (cassava), and some other plants. Annual world production of starch is well over 70 billion pounds, with much of it being used for non-food purposes, like making paper, cardboard, textile sizing, and adhesives.
• collagen is the most abundant protein found in mammals. Gelatin is denatured collagen, and is used in sausage casings, capsules for drugs and vitamin preparations, and other miscellaneous industrial applications including photography.
• casein, commercially produced mainly from cow's skimmed milk, is used in adhesives, binders, protective coatings, and other products.
• soy protein and zein (from corn) are abundant plant proteins. They are used for making adhesives and coatings for paper and cardboard.
• polyesters are produced by bacteria, and can be made commercially on large scales through fermentation processes. They are now being used in biomedical applications.

A number of other natural materials can be made into polymers that are biodegradable. For example:

• lactic acid is now commercially produced on large scales through the fermentation of sugar feedstocks obtained from sugar beets or sugar cane, or from the conversion of starch from corn, potato peels, or other starch source. It can be polymerized to produce poly(lactic acid), which is already finding commercial applications in drug encapsulation and biodegradable medical devices.
• triglycerides can also be polymerized. Triglycerides make up a large part of the storage lipids in animal and plant cells. Over sixteen billion pounds of vegetable oils are produced in the United States each year, mainly from soybean, flax, and rapeseed. Triglycerides are another promising raw material for producing plastics.

These natural raw materials are abundant, renewable, and biodegradable, making them attractive feedstocks for bioplastics, a new generation of environmentally friendly plastics. Starch-based bioplastics are important not only because starch is the least expensive biopolymer but because it can be processed by all of the methods used for synthetic polymers, like film extrusion and injection molding. Eating utensils, plates, cups and other products have been made with starch-based plastics.

Interest in soybeans has been revived, recalling Ford's early efforts. In research laboratories it has been shown that soy protein, with and without cellulose extenders, can be processed with modern extrusion and injection molding methods.

Many water soluble biopolymers such as starch, gelatin, soy protein, and casein form flexible films when properly plasticized. Although such films are regarded mainly as food coatings, it is recognized that they have potential use as nonsupported stand-alone sheeting for food packaging and other purposes.

Starch-protein compositions have the interesting characteristic of meeting nutritional requirements for farm animals. Hog feed, for example, is recommended to contain 13-24% protein, complemented with starch. If starch-protein plastics were commercialized, used food containers and serviceware collected from fast food restaurants could be pasteurized and turned into animal feed. Polyesters are now produced from natural resources-like starch and sugars-through large-scale fermentation processes, and used to manufacture water-resistant bottles, eating utensils, and other products.

Poly(lactic acid) has become a significant commercial polymer. Its clarity makes it useful for recyclable and biodegradable packaging, such as bottles, yogurt cups, and candy wrappers. It has also been used for food service ware, lawn and food waste bags, coatings for paper and cardboard, and fibers-for clothing, carpets, sheets and towels, and wall coverings. In biomedical applications, it is used for sutures, prosthetic materials, and materials for drug delivery.

Triglycerides have recently become the basis for a new family of sturdy composites. With glass fiber reinforcement they can be made into long-lasting durable materials with applications in the manufacture of agricultural equipment, the automotive industry, construction, and other areas. Fibers other than glass can also be used in the process, like fibers from jute, hemp, flax, wood, and even straw or hay. If straw could replace wood in composites now used in the construction industry, it would provide a new use for an abundant, rapidly renewable agricultural commodity and at the same time conserve less rapidly renewable wood fiber.

The widespread use of these new plastics will depend on developing technologies that can be successful in the marketplace. That in turn will partly depend on how strongly society is committed to the concepts of resource conservation, environmental preservation, and sustainable technologies. There are growing signs that people indeed want to live in greater harmony with nature and leave future generations a healthy planet. If so, bioplastics will find a place in the current Age of Plastics.