What is a functional woven bag? It is a woven bag with certain unique properties, such as aging-resistant woven bag, transparent woven bag, antistatic woven bag, antibacterial woven bag and other woven bags with excellent physical and chemical properties, etc. These woven bags have excellent performance, high production technology, and high product grade and added value.
Causes of plastic aging
The polymer has a fatal weakness, which is that it will age in the atmosphere of the woven bag factory. When the polymer is exposed to light and oxygen during processing, storage, transportation, and use, the macromolecules will degrade inside, making their physical and mechanical properties Deterioration, or even loss of its use value is what we usually call "aging". The weakness of polypropylene resin is very prominent. The main factor that promotes the aging of plastics is the ultraviolet rays in the sunlight, especially the wavelength of 290-400nm. It is the non-woven bag manufacturer that destroys the chemical bonds of the polymer and triggers the automatic oxidation reaction to cause aging and degradation. The most sensitive wavelength of polypropylene is 310nm, and the most sensitive wavelength of polyethylene is 300nm. How to suppress and slow down the effect of this photodegradation, so that the polymer ages slowly and has a long service life? After the efforts of scientists, it was found that adding a small amount of stabilizers (also known as anti-aging agents) to manufacturers of light shopping bags can achieve this goal.
Definition and classification of light stabilizers
Anything added to plastics that can inhibit or reduce photodegradation and improve the light resistance of materials is called a light stabilizer. Commonly used classification methods of light stabilizers are classification according to chemical structure and classification according to action mechanism. According to the chemical structure, it can be divided into: salicylates, benzophenones, benzotriazoles, triazines, substituted acrylonitriles, benzamides, organic nickel complexes, hindered amines and others . According to the mechanism of action, it can be divided into light shielding agent, ultraviolet absorber, quencher and free radical scavenger. Visually speaking, these four light stabilization methods are like the four lines of defense that form the light stabilizer in the compound layer. Each line of defense can inhibit the destruction of ultraviolet rays, but in actual use and formulation, it should be used according to the product. Depending on the environment and requirements.
Mechanism of light stabilizer
(1) Light shielding agent
Light shielding agent, also known as sunscreen agent, is a kind of substance that can absorb and reflect ultraviolet light. Its existence is like setting up a barrier between the polymer and the radiant light, so that the light cannot directly hit the inside of the polymer, thus effectively Inhibit photoaging. The specific substances for this function are mainly titanium dioxide (rutile type), zinc oxide and carbon black in some inorganic fillers and pigments (the channel method is better). The use of sunscreens to isolate harmful UV rays from polymers to prevent future problems is a very effective protective measure, which constitutes the first line of defense for light stabilization. Most of these materials have a wide range of sources and low prices. Unfortunately, their coloring greatly limits their scope of application. It can only be used for coloring products, not for transparent products.
(2) Ultraviolet absorbent
This type of stabilizer is the main body of the light stabilizer. It can strongly absorb ultraviolet light and convert its energy into harmless heat energy. This constitutes the second line of defense for light stabilization. There are many kinds of such substances, which can be divided into:
① Salicylic acid esters: this is the earliest application of ultraviolet absorbers, originally used for cellulose plastics, but this type of stabilizer itself has a very low ability to absorb ultraviolet light, and the absorption wavelength range is narrow (less than 340nm) However, its compatibility with resin is very good and the price is low. Its disadvantage is that it tends to yellow the product, so it is rarely used in the production of aging-resistant woven bags.
② Benzophenone is the largest output and most widely used UV absorber. This type of stabilizer has a wide absorption wavelength range and almost has strong absorption in the entire ultraviolet region. There are many varieties for different The variety of plastics should be selected appropriately.
③ The benzotriazole ultraviolet absorber is the first of its kind from Ciba-Geigy in Switzerland. It has a high stability and has developed rapidly since its inception. Nowadays, the variety and quantity of light stabilizers are second only to benzophenone. This type of ultraviolet absorber absorbs a wide range of ultraviolet light, and can effectively absorb ultraviolet light of 300-400nm, and almost does not absorb visible light above 400nm, so there is no disadvantage of coloring. Common brands UV-326, UV327.
In addition to the above three types of ultraviolet absorbers, there are also substituted acrylonitrile and triazine ultraviolet absorbers, the former can absorb ultraviolet light of 290-320nm, the latter can strongly absorb 300-400nm ultraviolet light.
(3) Quencher
Quencher, also known as deactivator, can be intuitively understood as the third line of defense for light stabilization, that is, unshielded or absorbed ultraviolet light, when absorbed by the polymer, the polymer is in an unstable "excited state" In order to prevent it from further decomposing and generating active free radicals, the quencher can eliminate the excitation energy from the excited polymer molecules and return it to a low energy state to achieve the purpose of light stability.
This type of light stabilizer has a prominent stabilizing effect on polyolefins, and is mostly used in films and fibers. They have very little solubility in solvents, have excellent washing durability when used in fibers, and have the function of dye aids. However, nickel complexes have a green color and have the disadvantage of coloring products, and because they mostly contain sulfur atoms, they have a tendency to change color during high-temperature processing, which limits their application and is not suitable for transparent products. It is used in combination with benzophenone, benzotriazole, etc., and has a good synergistic effect.
(4) Free radical trapping agent
Free radical scavenger is referred to as hindered amine (HALS). It is a light stabilizer developed in recent years. It is especially suitable for polyolefin, polystyrene, polyurethane and other plastics. Its stabilizing efficiency is several times higher than that of ultraviolet absorbers. Their mechanism of action has not yet been determined, and the capture of free radicals is a major function. This function can be intuitively understood as the fourth line of defense for light stabilization, that is, once the polymer absorbs this ultraviolet light and decomposes it produces automatic oxidation After the reactive free radicals are reacted, in order to prevent the chain oxidation reaction from spreading, the trapping agent captures the active free radicals and makes them into stable molecules to achieve the purpose of light stabilization. Due to its superior performance, it has replaced the traditional light stabilizer and become the mainstream of the light stabilizer consumer market.
Performance requirements of light stabilizers
The ideal light stabilizer should have the following conditions:
(1) It can effectively eliminate or weaken the damaging effect of ultraviolet light on the polymer without affecting other properties of the polymer.
(2) The light stabilizer itself has excellent light stability and cannot be destroyed by light.
(3) It has good compatibility with polymers, non-volatile, non-migrating, and is not extracted by water and solvents.
(4) Low absorption of visible light, no coloration and no color change.
(5) It has good thermal stability and chemical stability, and is stable during processing without affecting the processing performance of the polymer.
Light stabilizer commonly used in polypropylene woven bags
(1) Titanium dioxide
(2) UV-531 chemical name: α-hydroxy n-octyloxybenzophenone
It can strongly absorb ultraviolet light with a wavelength of 270-330nm. It is suitable for polypropylene with an amount of 0.1% -0.5%. Many countries permit plastic products for food contact. Beijing Additive Auxiliaries researches all productions under the brand name GW-531; many companies in the United States and Japan have production.
(3) UV-326 chemical name: 2- (2’-hydroxy-3’-tert-butyl-5-methylphenyl) -5’-chlorophenylpropanetriazole
It can effectively absorb ultraviolet light with a wavelength of 270-380nm, and has excellent stabilizing effect. It is suitable for polypropylene, with a general dosage of 0.1% -3%, low toxicity, and many countries allow plastic products used for food contact. It is produced in Tianjin Lisheng Chemical Factory in China; Beijing Additive Auxiliaries researches all production, and the current brand name is GW-326; Ciba-Geigy (Ciba Precision) in Switzerland is also produced abroad.
(4) Chemical name of UV-327: 2- (2’-hydroxy-3 ’, 5’-di-tert-butylphenyl) -5chlorophenylpropanetriazole
Features and uses are similar to UV-326.