Effect of Sterilization Techniques on Polymers

Transcription

1 Effect of Sterilization Techniques on Polymers Contents of Presentation Introduction to Polymers Properties and Stability of Polymers Affect of Ionising Radiation and Ethylene Oxide on Polymers The need to test for effects

2 Introduction to Polymers Health Care Products made from Polymers Catheters Artificial limbs (legs, feet, arms) Dental fillings and bridges Disposable process equipment Disposable surgical clothes and instruments Plasters - some Eyeglass frames and lenses Wound dressings 5 year shelf live Metered Dose Inhalers (MDI) Medical implants (e.g. Hip joint replacements, cranial and spinal implants)

3 What are Polymers? Polymers are high molecular weight molecules, which form long molecular chains built up by repetition of low molecular weight, simple chemical species (monomers) - Poly (from the Greek) many - Meros (from the Greek) - parts Polymers are.. many chemical links chained together Monomer Polymer The Structure of Polymers The basic makeup of many polymers is carbon and hydrogen Other elements can also be involved - Oxygen, chorine, fluorine, nitrogen, silicon, phosphorous, and sulphur are other elements found in the molecular makeup of polymers. Polyvinyl chloride (PVC) contains chlorine Nylon (polyamide) contains nitrogen Teflon (PTFE) contains fluorine Polyester and polycarbonates contain oxygen

4 Basics of Polymer Structure The simplest polymer structure is polyethylene (thermoplastic) The repeat units (monomers) join chemically (polymerisation) end-on- end to produce linear chain-like polymer molecules n(ch2=ch2) ethylene monomer CH3(CH2-CH2)n-1CH3 polyethylene polymer Typically n = 1,000 to 10,000 High molecular weights 28,000 to 280,000 General Classes of Polymers Thermoplastics - Can be repeatedly melted upon the application of heat recyclable because of this - Can be amorphous or semi-crystalline Thermosets - Rigid materials that can withstand higher temperatures than elastomers and plastics - they do not melt - Often filled and reinforced with fibrous or particulate fillers Rubbers - Usually sulphur or peroxide cross- linked - Materials that can stretch many times their original length - Do not melt upon application of heat

5 Structure of Thermoplastics Thermoplastics have primary chemical bonds (covalent) between atoms in chain, and weaker secondary bonds between chains which break down on heating causing softening Thermoplastics tend to be flexible Structure of Thermosets Thermoset plastics have strong primary bonds within and between (cross links) chains which do not break down on heating, hence no softening. Thermoset plastics tend to be rigid

6 Examples of Thermoplastics, Thermosets and Rubbers Thermoplastics POM- Acetal, PA - Polyamides, LDPE, HDPE, PP etc. Polyolefins PEEK- Polyetheretherketone, PPS- Polyphenylenesulphide Thermosets PF - phenolic resins, UF - urea resins, MF - melamine resins, Epoxy resins PU polyurethanes, PE polyesters Rubbers NR - Natural rubber, BR Polybutadiene, IR Polyisoprene, SBR - Styrene- butadiene rubber, EPDM - Ethylene-propylene-diene terpolymers NBR - Nitrile rubber, FR Fluoroelastomers Also blends of rubbers and plastics are possible Effect of Ionising Radiation and Ethylene Oxide on Polymers

7 Stabilisation of Polymers Ionising Radiation will generate free radicals in the Polymer, which can cause degradation due to: Chain scission Cross-linking Stabilisers can be added to the polymer to help protect it during sterilization and during its service life Different classes of stabiliser: Chain breaking antioxidants that react with free radicals, e.g. Phenolic antioxidants Compounds that decompose the peroxides/hydroperoxides formed in the polymer when the radicals react with oxygen, e.g. organo-phosphorous compounds Comparison Ethylene oxide vs Ionising Radiation Attributes of Ethylene Oxide (EtO) Sterilization Can leave toxic residuals or by-products in the polymer Has limited ability to penetrate into the polymer Can sterilize almost every plastic Does not degrade polymers and so can be used for articles that require to be repeatedly sterilized, e.g. hospital products Can be used on heat sensitive polymers as alternative to steam Attributes of Ionising Radiation Sterilization May degrade some polymers Has excellent penetration Does not leave toxic residuals

8 Summary of Potential Affects of Ionising Radiation and Ethylene Oxide on Polymers Ionising Radiation Chain scission reduces overall molecular weight Cross-linking will increase hardness, modulus, cause flex cracking etc Free radical reactions can alter the chemical structure of species (polymer related and additives) within the material Potential to generate low ph (i.e. acidic) species and non-volatile higher molecular weight species Ethylene Oxide Toxic and highly reactive gas that can leave residuals (see ISO ) Ethylene glycol formed upon reaction with water Less affect on physical properties than ionising radiation Potential to react with polymer molecules and additives and alter chemistry change in overall toxicity Potential Undesirable Affects of Irradiation Change in molecular weight, e.g. reduction due to chain scission Increase in cross-link density, leading to changes in modulus, hardness etc Change in colour, e.g. yellowing from oxidation of surface Generation of an odour due to volatiles formed by reactions with the polymer molecules and/or additives in the polymer

9 Affect of Ionising Radiation (Gamma and Electron Beam) on Polymers Competing chemical reactions result in either : Chain scission reduction in molecular weight Cross-linking increase in molecular weight Of the two - Reduction in molecular weight the least desirable More severe impairment of mechanical properties Hence, polymers more prone to chain scission (e.g. PP and PTFE) are classed as less resistant to ionising radiation that those (e.g. PS and PE) that tend towards cross-linking Resistance to ionising radiation varies greatly: Chemical structure Presence of fillers, e.g., glass fibres, mineral fillers Analysis and Testing Techniques Analysis of polymer products before and after sterilization to: Determine influence on Extractables and Leachables Effect on physical properties Strength Colour Smell

10 Critical Gamma Radiation Dose for a Selection of Common Polymers Thermosets Critical Dose (kgy) Plastics Critical Dose (kgy) Rubbers Critical Dose (kgy) Polyester + glass 10,000 PET 1000 EPDM 400 Polyurethane 10,000 Polysulphone 700 PU 300 Silicone + mineral 10,000 Polystyrene 600 SBR 300 Epoxy resin 7,000 UPVC 300 NBR 100 Silicone (unfilled) 1,000 Polyamides 300 Hypalon 100 Polyester + mineral 700 Polycarbonate 250 Polysulphide 90 MF resin 40 Polyethylene 100 Butyl 40 Acetal 15 Polypropylene 10 Silicone 40 Polyester (unfilled) 3 PTFE 4 Fluorocarbon 8 Conclusions of Presentation Wide range of polymers and polymer-based materials used in health care products Stability of polymers varies according to: Molecular structure Presence of stabilizers Type and levels of other additives present, e.g. Glass fibres Need to undertake tests to characterise the effect of sterilization on properties Ionising radiation and Ethylene oxide can both: Potentially alter the structure and physical properties of polymers Alter the extractables and leachables profile

11 Thank-you for listening. Any questions?