Gamma Radiation Resistance

Gamma Radiation Resistance of Polymers

Importance of Radiation & Sterilization

Most polymers can be degraded by photolysis to give lower molecular weight molecules. Electromagnetic waves with the energy of visible light or higher energy levels are usually involved in such reactions. These EMW include:

  • Ultraviolet light
  • X-rays and
  • Gamma rays

Among several types of radiations used currently for material testing, gamma radiation is the most common because of its high availability in research or industrial irradiators.

Gamma radiations are used for sterilization processes in medical devices, food industry as well as in nuclear power plants or aerospace.

Gamma radiation resistance characterizes the ability of polymers
to withstand sterilization methods

Radiation resistance is characterized by the half value dose of significant changes in mechanical properties such as elongation at break, flexural strength at break etc. of thermoplastics, elastomers, all aromatic polymers, as well as composite materials. The half-value-dose means the absorbed dose that reduces a property to 50% of its initial value under defined environments.

Loss of elongation is a commonly used to measure the effect of irradiation because
it equates to a brittleness failure

Check out more on Gamma Radiation Resistance:

 » Gamma Radiation Resistances of Various Polymers
 » Change in Mechanical Properties or Physical Appearance Upon Irradiation
 » Factors Impacting Radiation Resistance of Polymer

Impact of Radiation on Mechanical Properties or Physical Appearance of Polymers

Distintigration of <sup>60</sup>Co
Distintigration of 60Co
As mentioned above, polymer resins can tolerate gamma irradiation to varying degrees making them suitable for applications requiring sterility. The primary sources of industrial use gamma radiation are: Cobalt 60 (60Co) and Cesium 137 (137Cs). They emit gamma rays during their radioactive decay.

Gamma rays are a penetrating form of radiation which easily pass through plastics. They break the covalent bonds of DNA killing bacteria and other microbes exposed to the radiation.

Ionizing rays of gamma radiation can cause following changes in polymers:

  • Discolor or yellowing effect
  • Change in mechanical properties (varies by material)
  • Crosslinking – increased tensile strength, decreased elongation
  • Chain scission – reduced tensile strength and elongation

Each polymer reacts differently to ionizing radiation. Hence, overall dosage rate varies and must be limited according to the polymer.

Elongation Retention
(Source: Foster Corporation)

Irradiation and Polymers

  • Polyethylene in general crosslinks on irradiation, although there is a chain scission mechanism as well. Crosslinking of PE upon irradiation increases its tensile strength. However, polyethylene can be stabilized to make it gamma radiation resistant. High-density polyethylene is not as stable as medium density polyethylene and low-density polyethylene, linear low-density polyethylene.

  • Aromatic polymers (e.g. with benzene rings) are radiation resistant. Polymers such as PET, PU, PSU, PC  etc. can easily sterilized due to presence of benzene ring.

  • Aliphatic polymers exhibit degrees of resistance depending upon their levels of unsaturation and substitution.

  • Highly amorphous materials are generally radiation resistant then semi-crystalline polymers. The chain structure is capable of great ductility and they can tolerate many scissions without breaking up.

  • Polymers with butylene backbone such as ABS, PBT etc. lose impact strength on irradiation.

  • Nylon 10, 11, 12, and 6-6 are more stable than 6. Nylon film and fiber are less resistant.

  • Poly(methylmethacrylate) can satisfactorily withstand a single radiation sterilization dose both in the high molecular weight cast sheet form and as a molded item. It is not, however, suitable for repeated doses.

  • Poly(vinyl chloride) is suitable for single-dose radiation sterilization both in its unplasticized and plasticized forms.

  • Thermosets such as Phenol formaldehyde and urea formaldehyde are both reasonably suitable for irradiation sterilization.

  • Certain polymers such as fluoropolymers (PTFE, PVDF), polyacetals, polypropylene etc., however, do not stand up to gamma radiation exposure well for sterilization. PP undergoes slow degradation after irradiation.

Factors Affecting Gamma Radiation Resistance of Plastic

Radiation resistance of a material greatly depends on:

  • Polymer formulation (Additives, reinforcement, crosslinking in elastomers etc.)
  • Conditions of radiation exposure such as the environmental atmosphere, temperature, dose rate, mechanical stress, etc.

It is important to note that:

  • Additives such as stabilizers, antioxidants in polymers can reduce the effects of irradiation on mechanical properties or physical appearance (non-yellowing). For example: tint-based stabilizers when added to PVC help counteract color change in the polymer.

  • Inorganic fillers increase radiation resistance of polymer while Organic fillers usually decrease radiation resistance.

    Certain additives have a protective action and can reduce the effect of radiation on plastics

  • Thin parts sections, films, fibers present in the product can allow excessive exposure thus causing polymer degradation.

  • Molding which are strong in the axis of orientation but weak in the cross-flow axis becomes weaker after irradiation.

Gamma Radiation Resistances of Various Polymers

Click to find polymer you are looking for:
A-C     |      E-M     |      PA-PC     |      PE-PL     |      PM-PP     |      PS-X

Polymer Name Min Value (°C)
ABS - Acrylonitrile Butadiene Styrene Good
ABS Flame Retardant Poor
ABS High Heat Good
ABS High Impact Fair
ABS/PC Blend - Acrylonitrile Butadiene Styrene/Polycarbonate Blend Good
ABS/PC Blend 20% Glass Fiber Good
ABS/PC Flame Retardant Poor
ASA - Acrylonitrile Styrene Acrylate Good
ASA/PC Blend - Acrylonitrile Styrene Acrylate/Polycarbonate Blend Good
ASA/PC Flame Retardant Poor
ECTFE - Ethylene Chlorotrifluoroethylene Good
ETFE - Ethylene Tetrafluoroethylene Good
EVA - Ethylene Vinyl Acetate Fair
FEP - Fluorinated Ethylene Propylene Good
HDPE - High Density Polyethylene Fair
HIPS - High Impact Polystyrene Poor
HIPS Flame Retardant V0 Poor
LCP - Liquid Crystal Polymer Good
LCP Carbon Fiber-reinforced Good
LCP Glass Fiber-reinforced Good
LCP Mineral-filled Good
MABS - Transparent Acrylonitrile Butadiene Styrene Fair
PA 11 - (Polyamide 11) 30% Glass fiber reinforced Fair
PA 11, Conductive Fair
PA 11, Flexible Fair
PA 11, Glass Filled Fair
PPA 11 or 12 Fair
PA 11, Rigid Fair
PA 12 (Polyamide 12), Conductive Fair
PA 12, Fiber-reinforced Fair
PA 12, Flexible Fair
PA 12, Glass Filled Fair
PA 12, Rigid Fair
PA 46 - Polyamide 46 Fair
PA 46, 30% Glass Fiber Fair
PA 6 - Polyamide 6 Fair
PA 6-10 - Polyamide 6-10 Fair
PA 66 - Polyamide 6-6 Fair
PA 66, 30% Glass Fiber Fair
PA 66, 30% Mineral filled Fair
PA 66, Impact Modified, 15-30% Glass Fiber Poor
PA 66, Impact Modified Fair
PA 66, Impact Modified Poor
Polyamide semi-aromatic Fair
PAI - Polyamide-Imide Good
PAI, 30% Glass Fiber Good
PAI, Low Friction Good
PAR - Polyarylate Good
PARA (Polyarylamide), 30-60% glass fiber Fair
PBT - Polybutylene Terephthalate Good
PBT, 30% Glass Fiber Good
PC (Polycarbonate) Good
PC (Polycarbonate) 20-40% Glass Fiber Good
PC (Polycarbonate) 20-40% Glass Fiber Flame Retardant Poor
PC - Polycarbonate, high heat Good
PC/PBT Blend - Polycarbonate/Polybutylene Terephthalate Blend Good
PE - Polyethylene 30% Glass Fiber Fair
PEEK - Polyetheretherketone Excellent
PEEK 30% Carbon Fiber-reinforced Excellent
PEEK 30% Glass Fiber-reinforced Excellent
PEI - Polyetherimide Good
PEI, 30% Glass Fiber-reinforced Good
PEI, Mineral Filled Good
PESU - Polyethersulfone Good
PESU 10-30% glass fiber Good
PET - Polyethylene Terephthalate Good
PET, 30% Glass Fiber-reinforced Good
PET, 30/35% Glass Fiber-reinforced, Impact Modified Fair
PET, 30/35% Glass Fiber-reinforced, Impact Modified Poor
PETG - Polyethylene Terephthalate Glycol Good
PE-UHMW - Polyethylene -Ultra High Molecular Weight Fair
PFA - Perfluoroalkoxy Good
PI - Polyimide Excellent
PMMA - Polymethylmethacrylate/Acrylic Good
PMMA (Acrylic) High Heat Good
PMMA (Acrylic) Impact Modified Fair
PMMA (Acrylic) Impact Modified Good
PMP - Polymethylpentene Good
PMP 30% Glass Fiber-reinforced Good
PMP Mineral Filled Good
POM - Polyoxymethylene (Acetal) Fair
POM (Acetal) Impact Modified Fair
POM (Acetal) Low Friction Fair
POM (Acetal) Mineral Filled Fair
PP - Polypropylene Poor
PP - Polypropylene 10-20% Glass Fiber Poor
PP, 10-40% Mineral Filled Poor
PP, 10-40% Talc Filled Poor
PP, 30-40% Glass Fiber-reinforced Poor
PP (Polypropylene) Copolymer Poor
PP (Polypropylene) Homopolymer Poor
PP, Impact Modified Poor
PPA - Polyphthalamide Good
PPE - Polyphenylene Ether Fair
PPE, 30% Glass Fiber-reinforced Fair
PPE, Flame Retardant Poor
PPE, Impact Modified Fair
PPE, Impact Modified Poor
PPE, Mineral Filled Fair
PPS - Polyphenylene Sulfide Good
PPS, 20-30% Glass Fiber-reinforced Good
PPS, 40% Glass Fiber-reinforced Good
PPS, Conductive Good
PPS, Glass fiber & Mineral-filled Good
PPSU - Polyphenylene Sulfone Excellent
PS (Polystyrene) 30% glass fiber Good
PS (Polystyrene) Crystal Good
PS, High Heat Good
PSU - Polysulfone Good
PSU, 30% Glass finer-reinforced Good
PSU Mineral Filled Good
PTFE - Polytetrafluoroethylene Good
PTFE, 25% Glass Fiber-reinforced Good
PVDF - Polyvinylidene Fluoride Good
SAN - Styrene Acrylonitrile Good
SAN, 20% Glass Fiber-reinforced Good
SMMA - Styrene Methyl Methacrylate Good
SRP - Self-reinforced Polyphenylene Good
XLPE - Crosslinked Polyethylene Good

Commercially Available Polymer Grades with Gamma Radiation Resistance

Disclaimer: all data and information obtained via the Polymer Selector including but not limited to material suitability, material properties, performances, characteristics and cost are given for information purpose only. Although the data and information contained in the Polymer Selector are believed to be accurate and correspond to the best of our knowledge, they are provided without implied warranty of any kind. Data and information contained in the Polymer Selector are intended for guidance in a polymer selection process and should not be considered as binding specifications. The determination of the suitability of this information for any particular use is solely the responsibility of the user. Before working with any material, users should contact material suppliers in order to receive specific, complete and detailed information about the material they are considering. Part of the data and information contained in the Polymer Selector are genericised based on commercial literature provided by polymer suppliers and other parts are coming from assessments of our experts.

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