UV Light Resistance

What is ultraviolet (UV) light?
What is the effect of UV light on plastics?
What plastics show good UV resistance?
What prevents the damage of plastics by UV light?
What test methods determine plastic material behavior in UV light?
What are the values of UV resistance behavior of various polymers?

What is ultraviolet (UV) light?

Ultraviolet light is a part of the electromagnetic spectrum. It is at the higher end of energy compared to visible light. It is followed by X-rays and Gamma rays in terms of energy. UV energy absorbed by plastics can excite photons, which then create free radicals.

UV light is probably the most damaging environmental factor for plastics. Although to be fair to plastics, it attacks, to a greater or lesser extent, most other materials as well. All applications of plastics that are used outdoors are thus at risk. This includes roofing and window frames for vehicles. While many pure plastics cannot absorb UV radiation, the presence of catalyst residues and other impurities will often act as receptors, causing degradation.

Elecromagnetic Spectrum

The Electromagnetic Spectrum

What is the effect of UV light on plastics?

The UV light breaks down the chemical bonds in a polymer by photodegradation. This ultimately causes a change in appearance and deterioration in properties. It leads to discoloration. Primarily yellowing or whitening ('chalking') is most apparent. But, underneath, there is usually the beginning of a loss of physical properties. These include impact strength, tensile strength, and elongation. UV light can cause color change and degradation of physical properties, especially in:

Polyolefins
Polyvinyl chloride (PVC)
Polycarbonate (PC), and
Polyurethane (PU)

Hence, any attempt to design plastic parts without a clear understanding of the degradation mechanisms induced by the environment would result in a premature failure of the product.

Learn to Minimize the Discoloration of PVC Products »

What plastics show good UV resistance?

Note: UV radiation attacks all types of polymers. But a few polymers (acrylonitriles & methyl methacrylates) show better UV resistance than most.

What prevents the damage of plastics by UV light?

Plastics get damaged due to their oxidation caused by UV light. The counter-measures to prevent/terminate oxidation of plastics by UV light include:

coating,
introducing pigments that screen out the rays, or
neutralizing the UV energy within the compound and dissipating it.

Also, there exist many more technologies such as polymeric stabilizers, concentrates and masterbatches, fine particle technologies, etc. These help in preventing UV radiation from reaching the polymer. Thus, it helps to avoid damage. Some of the technologies are listed below.

Exploring screening pigments

Carbon black is the most effective screening pigment. However, its applications are limited to black-colored products.
Titanium dioxide is also used. But, it is expensive.
Calcium carbonate can also have a screening effect. But, usually at a high loading, it might impair mechanical properties.

Mechanism of UV absorbers

UV absorbers are receptive to UV radiation. But, they do not themselves degrade rapidly. They convert UV energy and dissipate it harmlessly as heat. They prevent the oxidation caused by UV radiation. However, they should not be confused with antioxidants, which are not UV deactivators as such.

Benzophenones are good general-purpose UV absorbers for clear polyolefin systems. They can also be used in pigmented compounds.
Benzotriazoles are used mainly in polystyrene and PVC. But they can also be used in acrylics and polycarbonates, and in polyurethanes and unsaturated polyesters. They also improve the light stability of styrenics, polyacetals, epoxies, urea, and melamine.

Structure of Benzophenone and Benzotriazole

(A) Structure of Benzophenone; (B) Structure of Benzotriazole
Source: ResearchGate

Role of UV stabilizers and quenchers

Ultraviolet stabilizers work, unlike UV absorbers. They inhibit bond rupture by chemical means or dissipate the energy to lower levels that do not attack the bonds.
Quenchers reduce the UV energy by means of deactivating metal ions. In effect, they intercept the energy before it can break any molecular bonds. But, they work in a different way from absorbers.

Scavenging free radicals - HALS for enhanced polymer protection

Scavengers act by inhibiting the free radicals generated by UV light. Thus, stopping any further decomposition. The most important are hindered amine light stabilizers (HALS). They are efficient scavengers. They function by inhibiting the degradation of a polymer that has already formed free radicals.

HALS have the advantage that they bind additives to the polymer at the molecular level. This causes less antagonism towards other additives. They can be used with most polymers. Polymeric HALS offer:

Superior compatibility
Low volatility
Excellent resistance to extraction, and
Contribute to heat stability

A combination of two high molecular weight grades gives a good balance of properties for greenhouse film. Low density polyethylene (LDPE) film is mainly used in HALS.

Synergists with HALS

In conjunction with other light stabilizers, HALS can exhibit synergistic effects. These are being actively explored. For example, some cyanoacrylate-based UV absorbers offer particular benefits in:

acrylonitrile butadiene styrene (ABS) and polyamide (PA)
individual components of rigid or plasticized PVC, styrene butadiene rubber (SBR), and polyurethane foams.

What test methods determine plastic material behavior in UV light?

There exist several test methods to predict the behavior of plastic material to UV light. These test methods characterize material performance when subjected to specific and well-defined factors. But, it is also important to note that no one test can be employed to test completely the effects of UV light on any material.

ASTM D2565 — It determines the xenon-arc exposure of plastics intended for outdoor applications.

ASTM D4459 — It determines the xenon-arc exposure of plastics intended for indoor applications.

ASTM D4329 — It determines the fluorescent ultraviolet (UV) lamp apparatus exposure of plastics.

ASTM G154 — It operates fluorescent ultraviolet lamp apparatus for exposure to non-metallic materials.

ISO 4892 — It determines the methods of exposure to laboratory light sources. It is a four-part standard covering different light sources.
- Part 1: General guidance
- Part 2: Xenon-arc exposure
- Part 3: Fluorescent UV exposure
- Part 4: Carbon-arc exposure

What are the values of UV resistance behavior of various polymers?

Polymer Name	Value
ABS - Acrylonitrile Butadiene Styrene	Poor
ABS Flame Retardant	Poor to Fair
ABS High Heat	Poor
ABS High Impact	Poor
ABS/PC Blend - Acrylonitrile Butadiene Styrene/Polycarbonate Blend	Fair
ABS/PC Blend 20% Glass Fiber	Fair
ABS/PC Flame Retardant	Poor
ASA - Acrylonitrile Styrene Acrylate	Good
ASA/PC Blend - Acrylonitrile Styrene Acrylate/Polycarbonate Blend	Good
ASA/PC Flame Retardant	Poor
ASA/PVC Blend - Acrylonitrile Styrene Acrylate/Polyvinyl Chloride Blend	Good
CPVC - Chlorinated Polyvinyl Chloride	Fair
ECTFE - Ethylene Chlorotrifluoroethylene	Good
ETFE - Ethylene Tetrafluoroethylene	Good
EVA - Ethylene Vinyl Acetate	Poor
FEP - Fluorinated Ethylene Propylene	Good
HDPE - High Density Polyethylene	Poor
HIPS - High Impact Polystyrene	Poor
HIPS Flame Retardant V0	Poor
Ionomer (Ethylene-Methyl Acrylate Copolymer)	Good
LCP - Liquid Crystal Polymer	Good
LCP Carbon Fiber-reinforced	Good
LCP Glass Fiber-reinforced	Good
LCP Mineral-filled	Good
LDPE - Low Density Polyethylene	Fair
LLDPE - Linear Low Density Polyethylene	Fair
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, Rigid	Fair
PA 11 or 12	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	Poor
PA 66, 30% Glass Fiber	Poor
PA 66, 30% Mineral filled	Poor
PA 66, Impact Modified, 15-30% Glass Fiber	Poor
PA 66, Impact Modified	Poor
Polyamide semi-aromatic	Fair
PAI - Polyamide-Imide	Excellent
PAI, 30% Glass Fiber	Excellent
PARA (Polyarylamide), 30-60% glass fiber	Good
PBT - Polybutylene Terephthalate	Fair
PBT, 30% Glass Fiber	Fair
PC - Polycarbonate	Fair
PC (Polycarbonate) 20-40% Glass Fiber	Fair
PC (Polycarbonate) 20-40% Glass Fiber, Flame Retardant	Poor
PC - Polycarbonate, high heat	Fair
PC/PBT Blend - Polycarbonate/Polybutylene Terephthalate Blend	Fair
PC/PBT blend, Glass Filled	Fair
PCTFE - Polymonochlorotrifluoroethylene	Good
PE - Polyethylene 30% Glass Fiber	Fair
PEEK - Polyetheretherketone	Good
PEEK 30% Carbon Fiber-reinforced	Good
PEEK 30% Glass Fiber-reinforced	Good
PEI - Polyetherimide	Fair
PEI, 30% Glass Fiber-reinforced	Fair
PEI, Mineral Filled	Fair
PESU - Polyethersulfone	Fair
PESU 10-30% glass fiber	Fair
PET - Polyethylene Terephthalate	Fair
PET, 30% Glass Fiber-reinforced	Fair
PET, 30/35% Glass Fiber-reinforced, Impact Modified	Poor
PETG - Polyethylene Terephthalate Glycol	Fair
PE-UHMW - Polyethylene -Ultra High Molecular Weight	Fair
PFA - Perfluoroalkoxy	Fair
PI - Polyimide	Excellent
PMMA - Polymethylmethacrylate/Acrylic	Good
PMMA (Acrylic) High Heat	Good
PMMA (Acrylic) Impact Modified	Fair
PMP - Polymethylpentene	Fair
PMP 30% Glass Fiber-reinforced	Fair
PMP Mineral Filled	Fair
POM - Polyoxymethylene (Acetal)	Poor
POM (Acetal) Impact Modified	Poor
POM (Acetal) Low Friction	Poor
POM (Acetal) Mineral Filled	Poor
PP - Polypropylene	Fair
PP - Polypropylene 10-20% Glass Fiber	Fair
PP, 10-40% Mineral Filled	Fair
PP, 10-40% Talc Filled	Fair
PP, 30-40% Glass Fiber-reinforced	Fair
PP (Polypropylene) Copolymer	Fair
PP (Polypropylene) Homopolymer	Fair
PP, Impact Modified	Poor
PPE - Polyphenylene Ether	Fair
PPE, 30% Glass Fiber-reinforced	Fair
PPE, Flame Retardant	Poor
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	Good
PS - Polystyrene	Poor
PS - Polystyrene, 30% Glass Fiber	Poor
PS (Polystyrene) Crystal	Poor
PS, High Heat	Poor
PSU - Polysulfone	Fair
PSU, 30% Glass finer-reinforced	Fair
PSU Mineral Filled	Fair
PTFE - Polytetrafluoroethylene	Good
PTFE, 25% Glass Fiber-reinforced	Good
PVC (Polyvinyl Chloride)	Good
PVC (Polyvinyl Chloride), 20% Glass Fiber-reinforced	Good
PVC, Plasticized	Fair
PVC, Plasticized Filled	Fair
PVC Rigid	Fair
PVDC - Polyvinylidene Chloride	Fair
PVDF - Polyvinylidene Fluoride	Good
SAN - Styrene Acrylonitrile	Poor
SAN, 20% Glass Fiber-reinforced	Poor
SMA - Styrene Maleic Anhydride Flame Retardant V0	Poor
SRP - Self-reinforced Polyphenylene	Good
XLPE - Crosslinked Polyethylene	Good

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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