What are Light Stabilizers (HALS)? Light Stabilizer Definition
A major class of light stabilizers includes the so-called hindered amine light stabilizers (abbreviated HALS). They are derivatives of 2,2,6,6-tetramethylpiperidine and are extremely effective stabilizers against photodegradation of most polymers.
HALS are potent scavengers and work by inhibiting the degradation of polymers that have formed free radicals, they do not absorb UV radiation but act to inhibit polymer degradation. They slow down photochemically induced degradation reactions in a manner similar to antioxidants. The mechanism of difference between antioxidants and HALS is that HALS reactions are cyclical, whereas antioxidants are not.
Commercially, hindered amine light stabilizers are now the most important light stabilizers, followed by benzophenones and benzotriazoles.
light stabilizer synonym
Hindered Amine Light Stabilizers (abbreviated as HALS)
light stabilizer additive
UV absorber
How do light stabilizers work? Mechanism of Light Stabilizers
The mechanism is not fully understood. Hydroperoxide decomposition and free radical scavenging certainly play a role, as does the regeneration of HALS, where the UV absorber is often consumed due to its operation. There are several theories as to how this works - perhaps through energy transfer, free radical termination (pictured below), or peroxide breakdown. Remarkable stabilization was achieved at relatively low concentrations, and it appears that HALS are actually regenerated by the stabilization process rather than being consumed by it. Theory suggests that hindered amines oxidize to form amine ethers, which are non-radical species.
The effectiveness of HALS systems does not depend on the thickness of the plastic product, so they are especially suitable for protecting surface layers and thin sections. Reagents are of low or high molecular weight. Polymeric HALS provide excellent compatibility, low volatility, excellent extraction resistance, and contribute to thermal stability. The combination of two high molecular weight grades provides a good balance of properties in greenhouse films, which is the main use of HALS in LDPE films.
Synergistic Effect of Light Stabilizer and UV Absorber
UV absorbers cannot absorb all the UV radiation to which a product is exposed. Some UV radiation penetrates the surface. Because of this, HALS are incorporated into polymers. These molecules work by scavenging any free radicals that do form – unlike UV absorbers, which prevent their formation by first removing free radicals from the system and then regenerating themselves. For this reason, most formulators use a combination of absorbents and HALS.
A synergistic combination of UV absorbers and HALS is optimal for stabilizing polymers. UV absorbers are governed by the Beer-Lambert law
Absorbance is therefore linearly related to the concentration of UVA (320 to 400 nm (for photocuring)), its molar absorptivity (extinction coefficient) and path length (coating thickness). HALS are free radical scavengers that are not subject to Beer's Law and work anywhere in the system.
UV Absorbers and Light Stabilizers Market and Trends
In 2015, the global market size of UV absorbers (including light stabilizers) for plastics and coatings was approximately RMB 13 billion, with a compound average growth rate (CAGR) of 3% to 4% in the next four years. This is attributed to industrial development in emerging markets and significant growth in demand for coatings globally. For example, automotive and industrial coatings drive the demand for polymer additives. With the high technological threshold for additive manufacturing and development, manufacturers of UV absorbers (including light stabilizers) are located in a few chemically developed countries. Growth opportunities exist in new markets and exploring new applications
