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Biodegradable

Background

The ever increasing global population is having a direct impact on consumption of natural and fossil fuels.  Not only are we depleting these finite resources but our consumer driven lifestyle means that we are disposing of ever larger quantities of waste that will not degrade but remain indefinitely in landfill.  The European Landfill Directive (1999) seeks to prevent or reduce as far as possible negative effects on the environment, in particular the pollution of surface water, groundwater, soil and air, and on the global environment, including the greenhouse effect, as well as any resulting risk to human health, from landfilling of waste, during the whole life-cycle of the landfill.

In order to reduce the volume and impact of landfill waste, a new generation of Biodegradable? products is required that will break down following disposal.  However to minimise consumption of fossil fuels, water and energy this new generation of Biodegradable? products must also be sustainable and preferably renewable.   The various issues relating to biodegradability and sustainability will be covered in this section. 

Revision of the micro and macro structure of polymers and fibres

Degradable materials are all polymers.  The properties of polymers depend on both the molecular structure (microstructure) and the arrangement of these molecules i.e. amorphous or semi-crystalline (macrostructure)

Molecular structure of polymers

Polymers (or macromolecules) are very large molecules made up of smaller units, called monomers or repeating units, covalently bonded together (Fig 1). 

Fig 1

A    is a monomer unit -  Is a covalent bond

Figure 1A polymer chain

The chainlike structure of polymeric materials is responsible for their intriguing mechanical properties.

Macro structure of polymers

Many properties of polymeric materials depend on the microscopic arrangement of their molecules. Polymers can have an amorphous or semicrystalline (partially crystalline) structure (Fig 2).

-          Amorphous polymers lack order and are arranged in a random manner

-           Semicrystalline polymers are partially organised in orderly crystalline structures.

Fig 2

Figure 2(a) Amorphous polymer (observe the entanglements among the polymer chains) and (b)

semicrystalline polymer

More information can be found on polymer architectures : (click here)