Plastic packaging systems define a set of packaging materials that are composed wholly or in substantial portion of plastic materials which contain or is intended to contain pharmaceutical formulations. They are very commonly used as packaging materials for most types of pharmaceutical dosage forms due to the several advantages they possess overglass containers.
Because plastic container is, or may be, in direct contact with the pharmaceutical formulations, they are usually made of materials which do not include in their composition any substance that can alter the efficacy or stability of the formulation, or present a risk of toxicity. This article mainly focused on plastic containers, their uses and compositions, types, ideal properties, formation/ moulding techniques, evaluation studies, advantages and disadvantages.
What are plastics?
The term “plastic” is a general common term used to describe a group of non-metallic substances, of natural, semi-synthetic or synthetic origins, consisting chiefly of one or more organic compounds (polymer) of high molecular weight, which can be moulded into the desired shapes and hardened for use when subjected to heat or pressure, with or without the addition of some additives. Plastics constitute about 20 % of weight of all pharmaceutical packaging. They are used for many different types of packs including
rigid bottles which serve as packaging systems for solid dosage forms (tabletsandcapsules)sterile plastic packaging systems for human blood and blood componentsplastic packaging systems for aqueous solutionsbags for parenteral solutionsinfusion dry powder and metered-dose inhalerssqueezable bottles for eye drops, ear drops and nasal spraysjarsprefillable syringesflexible tubessachets, blister packs and strip packscartridges, nebulizers, and vials etc.
Composition of Plastic Containers
Basically, plastics containers consist of organic materials whose molecules have high molar masses and are composed of a large number of repeating relatively small units referred to as monomers. When these monomers undergo a process known as polymerization, a plastic or a sequentially joined long chain of polymer is formed. This process of polymerization may involve various chemicals which assist the process, such as accelerators, initiators, solvents and catalysts, and as a result, are present in small degree in the plastic formed. These, if found in the plastic after polymerization are generally referred to as process residues.
Plastics may also incorporate processing aids e.g., styrenes, acrylics, calcium carbonates, lubricants, silicone oil etc., which are usually added to assist a process and additives (e.g., plasticizers, colouring matter, fillers/extenders, light stabilizers, reinforcement etc.,) which modify the plastic chemically or physically in some way. Most plastics derive their names from the type of polymer(s) used during manufacture. Virtually any desired property or characteristics can be achieved during plastic formation by proper manipulation of the properties of the polymer(s) and additives used.
Types of plastic packaging system
Plastic packaging system can broadly be divided into two categories: thermoplastics (thermosoftening plastics) and thermosets (thermosetting plastics).
a. Thermoplastics (Thermosoftening plastics)
These are heat softening materials which are usually rigid at operating temperatures but can be remelted and remoulded when exposed to high temperature and pressure. When frozen, however, thermoplastics become glass-like and subject to fracture. Examples of thermoplastics include but are not limited to the five most economical plastics – polyvinylchloride, polystyrene, polypropylenes, polyethylenes, and polyester. Others include nylon, polyvinylidene chloride, polycarbonate etc., Thermoplastics may be further classified into homopolymers which involves one type of monomers, e.g., ethylene polymerized to polyethylene, and copolymers, terpolymers etc., which involve two or more monomers of different chemical substances.
b. Thermosets (Thermosetting plastics)
They are called thermosets because they get distinctly infusible or insoluble when exposed to high temperature/ heat, and thus cannot be remelted and remoulded after their initial heat forming. They are produced by polymerization process involving a curing or vulcanization stage during which the materials become ‘set’ to a permanent state by heat and pressure. Further heating leads to the decomposition of the plastic. Thermosets usually contain additional additives (fillers and reinforcing agents) to obtain best quality. These materials are used as packaging material when good dimensional and heat stability are required. Examples of thermoset resins include phenol formaldehyde (originally known as bakelite), urea formaldehyde, melamine formaldehyde, epoxy resins (expoxies), and certain polyesters and polyurethanes. These materials are commonly used in the pharmaceutical industry as closures for glass and/or plastic containers, small cases as one time used for methanol cones, protective lacquers and enamels as applied internally and externally to metal containers and a range of adhesive systems.
Advantages of plastic containers
1.Plastic containers are not breakable. 2.They are light in weight and resistant to leakage. 3.They are cheap to manufacture 4.They can be easily moulded or remoulded 5.They have excellent finishing 6.Plastic containers are chemically inert and resistant to corrosion 7.They are collapsible
Disadvantages of plastic containers
8.Plastic containers have poor physical stability due to adsorption, absorption lightness and/or interactions between the formulation and the container 9.They have low heat resistant and poor ductility. 10.Most plastic containers are usually not as clear as glass, and, therefore, inspection of the contents is impeded.