How to choose antioxidants and light stabilizers!

Antioxidant

Antioxidant is a type of chemical substance.

Antioxidants should have the following conditions:

①Should have high antioxidant capacity;

②Good compatibility with resin, no precipitation;

③Good processing performance, non-volatile and non-decomposing at the processing temperature of high polymer;

④Good resistance to extraction, insoluble in water and oil;

⑤The color itself is best to be colorless or light-colored, so as not to pollute the product;

⑥Non-toxic or low-toxic;

⑦Low price

In fact, any kind of antioxidant can not fully meet these conditions.

Light stabilizer

The main functions of light stabilizers are: shielding light, absorbing and transferring light energy, quenching or capturing free radicals

Hindered amine light stabilizer (HALS) is a kind of organic amine compound with steric hindrance effect, because it has the function of decomposing hydroperoxide, quenching excited oxygen, trapping free radicals, and the effective group can be recycled and regenerated.

Ultraviolet light-absorbing light stabilizers are commonly known as ultraviolet light absorbers.

Both the quencher and the ultraviolet light absorber achieve the purpose of light stabilization by transferring light energy

Light shielding agents include carbon black, titanium dioxide, zinc oxide and the like

The three types of domestic light-shielding agents, ultraviolet light absorbers, and quenchers have been industrially used around the 1960s.
Although hindered amine light stabilizers have only begun industrial production in the mid-1970s, their products The increase rate of variety and output is much higher than the other three types of stabilizers, and it is the rising star of the plastic light stabilizer family
.

The principle of choosing antioxidants and light stabilizers

It should be determined comprehensively based on the types and models of plastic materials, processing equipment and process conditions, the types and amounts of other chemical additives, the use environment and deadlines of the products, and other factors
.
The following principles should be basically referred to when choosing antioxidants and light stabilizers for industrial use
.

(1) Compatibility
.
The polymers of plastic polymers are very polar, while the molecules of antioxidants and light stabilizers have different degrees of polarity, and the compatibility of the two is poor.
Usually, the antioxidants and light stabilizers are combined at high temperatures.
Combined with the polymer melt, the antioxidant and light stabilizer molecules are compatible with the polymer molecules when the polymer is cured
.
Within the formula dosage range, the antioxidants and light stabilizers must be melted at the processing temperature.
Special attention should be paid.
When designing the formula, the melting point or melting range of the solid antioxidant and light stabilizer should not be lower than the plastic polymerization.
The processing temperature of the object
.

It has been proven that the amorphous phase at the spherulite interface of the polymer crystal region is the most susceptible part of the polymer matrix to be oxidized, and the antioxidants with good solubility are concentrated in the areas where the polymer needs them most
.

(2) Migration
.
Plastic products, especially products with a small surface area to volume ratio (or mass ratio), oxidation mainly occurs on the surface of the product, which requires antioxidants and light stabilizers to continuously migrate from the inside of the plastic product to the surface of the product.
Play a role
.
However, if the migration speed to the product surface is too fast and the migration amount is too large, the antioxidant and light stabilizer will volatilize into the environment of the product surface, or the diffusing agent will be lost in other media in contact with the product surface.
In fact, it is inevitable and should be considered when designing the formula
.
When the antioxidants and light stabilizers have room for selection, the varieties with relatively large molecular weight and appropriately higher melting point should be selected, and the use amount of antioxidants and light stabilizers should be determined on the premise of the most severe use environment
.

(3) Stabilizer
.
Antioxidants and light stabilizers should remain stable in plastic materials, have little volatilization loss under the use environment and high temperature processing, do not change or develop color, and do not decompose (except for the antioxidants used for processing heat stabilization ), does not cause adverse chemical reactions with other additives, does not corrode mechanical equipment, and is not easily extracted by other substances on the surface of the product
.
Hindered amine light stabilizers are generally low-alkaline products.
When hindered amines are selected as light stabilizers in plastic materials, other acidic additives should not be included in the formulation, and corresponding plastic products cannot be used in acid environments
.

(4) Processability
.
When plastic products are processed, adding antioxidants and light stabilizers may change the resin viscosity and screw torque
.
If the antioxidant and light stabilizer have a large difference in the melting range of the resin, the phenomenon of anti-oxidant and light stabilizer drift or screw suppression will occur
.
When the melting point of the antioxidant and light stabilizer is lower than the processing temperature of 100℃ or more, the antioxidant and light stabilizer should be made into a certain masterbatch, and then mixed with the resin to process the product to avoid resistance in the product due to drift.
The distribution of oxygen agents and light stabilizers is uneven and the processing output decreases
.

(5) Environment and hygiene
.
Antioxidants and light stabilizers should be non-toxic or low-toxic, no dust or low dust, have no harmful effects on the human body in the processing, manufacturing and use of plastic products, no harm to animals and plants, and no harm to air, soil, and water systems.
Pollution
.

For agricultural film food packaging boxes, children’s toys, disposable infusions, and other plastic products that indirectly or directly contact food, drugs, and medical devices that contact the human body, not only should be selected that has passed the U.
S.
Food and Drug Administration (FDA) inspection and approval, or The types of antioxidants and light stabilizers allowed by the decree of the Commission of the European Communities, and the amount added should be strictly controlled within the maximum allowable limit
.

The oral toxicity test value of the light stabilizer UV-326 is LD50>5000 mg/kg, which is a relatively non-toxic chemical substance, but the European Commission’s decree still stipulates the maximum limit of UV-326 in plastic materials in contact with food.
, The maximum limit is 0.
5% in polypropylene and polyethylene, 0.
3% in polyethylene, and 0.
6% in polystyrene
.