A plastic is a material that contains an essential ingredient one or more polymeric organic substances of large molecular weight. Plastic Used as container for the product and as secondary packaging.

Advantages of plastic:
• Flexible and not easily broken
• Low density and light in weight
• Are cheap

Disadvantages of plastic :
• They are not as chemically inert as Type I glass
• They are not as impermeable to gas and vapour as glass
• They may posses an electrostatic charge which will attract particles
• Used for many types of pack include ng rigid bottles for tablets and capsules, squeezable bottles for eye drops and nasal sprays, jars, flexible tubes and strip and blister packs.


Factors responsible for plastics properties
• Chemical structure
• Molecular weight
• Crystallinity and orientation
• Cross-linking
• Addition of other agents

Chemical Structure
• Linear polymer chain
• Branched polymer chain

Molecular weight
• Melt flow index (MFI)
• Useful factor for characterization of polyolefins
• High melt (flow) indicate lower molecular weights & low melt (flow) indicate high molecular weights.
• Increase in MFI is related to :
   1. Ease of moulding
   2. Impact strength (decreases)
   3. Stress cracking resistance (decreaes)

Crystallinity and orientation
Crystallinity :
• Orderly compact structure of the molecular chain
• Polymer chain may twisted and tangled formation given an amorphous type polymer

Orientation
• The alignment of crystalline structure in polymeric materials so as to produce a highly aligned molecular structure.
• Materials are stretched just below or above their softening point .
• Depending on the degree of orientation, significant changes can occur in both the physical & chemical properties.
   1. Improving clarity
   2. Reducing to moisture & gas permeation
   3. improving chemical resistant

Cross-linking
• Joints between chains which occur in three dimensions.
• Reflected in physical properties, increasing, for example, polymer rigidity.
• Thermoset are cross-link.

Addition of other agents
• Antioxidants
• Stablizers
• Plasticizers
• UV absorbers
• Antistatics
• Dyes or pigments
• Lubricants
• Etc.

Important problems
  1. Sorption
  2. Desorption (Leaching)
  3. Permeation
  4. Photodegradation
  5. Polymer Modification
Two classes of plastic/polymer types are used and these are known as thermosets and thermoplastics.
Thermosets (Thermosetting plastics consist of those plastics that, when subjected to heat, normally will become infusible or insoluble, and as such cannot be remelted. These plastics are used when good dimensional and temperature stability are required. The formaldehyde plastics have been found the most used in the pharmaceutical industry as closures for glass and /or plastics containers.

Thermoplastics consist of those plastics that normally are rigid at operating temperatures but can be remelted and reprocessed.


Sterilization of Plastic as Pharmaceutical Packaging

Steam sterilization at temperature of 121o
  • Polypropylene
  • High density polyehthylene
  • Polycarbonate
  • PVC for certain application
  • All thermosets

Gas sterilization (Ethylene Oxide)
  • Cannot be used for containers of aqueous product because side-reaction products such as ethylene glycol and 2-chloroethanol are formed.
  • Ethylene oxide itself is carcinogenic.
  • Regulatory permissible limit have been established for residual levels of ethylene oxide. Packaged products are degassed prior to shipping or use.
  • Degassing properties depend upon geometry, heat history, storage conditions, contact with other plastics, and type of secondary packages used. Because of this complexity, degassing hold times must be determined for each product.
Irradiation
  • Can cause degradation or cross-linking of certain polymers.
  • Particularly serious for polyprolylene. Although a radiation stable form of PP has been developed, it may not suitable for multiple sterilizations.
  • PVC loses hydrochloric acid upon radiation, decomposing into unstable fragments, which may then cross-link. This dehydrochlorination lead to the formation of conjugated double bonds, which impart yellow discoloration.

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