Plastics are Different Polymers
Polymers are large molecules composed with the strength of covalent bonding. They are made up of repeating structural units that can be both synthesized and naturally occurring. Plastics, being the most common type of commercial polymer, are often referred to when mentioning polymers in layman conversation. However, polysaccharides, also being a type of polymeric material, are made up of units bound together by glycosidic bonds. Plastics do not have these types of bonds in their polymers, instead using different molecular bonds to form durable materials.
Polysaccharides Compose Different Substances
Substances such as cellulose, which is a majority component of wood, are composed through linked polysaccharides. Pectins, another type of structural polysaccharides, are found throughout plant parts and primary cell walls. These polysaccharides can easily get tangled among themselves, causing the substance to substantially thicken. Chitin, another natural polymer, is degradable and easily broken down via various enzymes secreted by organisms like bacteria.
Plastic is Largely Synthetic
Obviously, the production of non-natural plastic is a rather large industry among humans. Its synthesis forms large-massed molecules often entwined with other components so as to increase performance and durability. Petroleum and natural gas form the catalysts that enable commercial plastic production. Unfortunately, this raises a lot of ecological and long-term stability questions, as synthesized plastics aren't exactly biodegradable. Much of the plastic synthesized ends up polluting oceans, landfills and even the atmosphere through the release of toxic fumes once burned.
Polysaccharides Are Secreted Naturally
Organisms -- commonly bacteria -- secrete polysaccharides; fungi and algae emit these molecules so as to adhere to things much more readily. Pathogenic bacteria secrete thick layers of polysaccharides while others use them as protective barriers between the cell walls and outside world.
There is a Wide Range of Different Plastics
The recognized families of plastics include the ultra polymers, high-performance polymers, medium polymers and common (or commodity) polymers. PVC, polyvinyl chloride, is a common substance that is used in construction and infrastructure. Polyvinyl chloride is a mid-range, medium polymer with amorphous traits. Amorphous polymers from the ultra polymer family include polyamide imide and HTS. Semi-crystalline ultra polymers such as polyether ether ketone (known as PEEK) are often used in the engineering industry.