UV resistant acrylic

With the advent of the 5G era, information dissemination is comparable to the speed of light. An Internet celebrity with 100,000 fans takes a few photos and sends them to Weibo, Douyin, Kuaishou and other self-media platforms. In a flash, they can get countless likes and comments. , And quickly led to an Internet celebrity punching the ground.

Many shopping malls and tourist attractions are also firmly grasping this new trend. By creating unique and colorful acrylic beauty and new styles, the shopping malls and attractions atmosphere are perfectly integrated with various themes and festivals to attract and drive passenger flow. , Leading tourists to the new direction of clocking in.

The transparent acrylic Meichen has a crystal-like transparent texture, which can present a colorful visual effect, just like a beautiful handicraft, and it is beautifully photographed. Such an eye-catching beauty model has experienced wind and sun, but it can hardly escape the fate of aging and yellowing. This is also a major problem that has caused many businesses to realize later, headaches, and even cause disputes.

In daily life, disputes and claims caused by the yellowing of acrylic are not uncommon.

Why does the crystal clear acrylic Meichen quietly turn yellow?

First of all, this has to start with aging.

Acrylic is also known as plexiglass. Acrylic products placed outdoors will gradually age due to the combined effects of ultraviolet rays, oxygen, humidity and temperature. Among them, ultraviolet rays have the most serious impact on PMMA sheets.

When sunlight hits the surface of plexiglass, three phenomena of absorption, transmission, and reflection will generally occur. According to the laws of optics, it can be inferred that the part of the light quanta that is absorbed will cause the plexiglass to produce an aging effect.

After the ultraviolet absorption process, the structure of acrylic has changed on the molecular scale, that is, the molecular chain breaks are degraded and cross-linked, which leads to changes in physical and chemical properties, especially optical properties on the physical level.

Due to the decomposition reaction, the molecular weight is reduced, and a large number of chromophores such as carbonyl groups are produced, which leads to yellowing, silver streaks, and even embrittlement and mechanical properties of the board. The most obvious of these is the visual yellowing. . A series of experiments have proved that the aging of plexiglass under the action of light is mainly caused by the participation of oxygen in the air, which causes the main chain of plexiglass to break; therefore, the combined effect of light and oxygen is the main factor in the decrease of the molecular weight of plexiglass.

Intermolecular cross-linking makes the molecules produce larger molecules, forming a network-like structure, and the cross-linking between macromolecules leads to the embrittlement of the glass, which ultimately intensifies the aging rate. Therefore, as the exposure time increases, the degree of aging of the plexiglass surface will also increase.

Spectral analysis shows that the characteristic absorption peak of methyl methacrylate for ultraviolet light is 290nm～330nm, and sunlight contains a small amount of ultraviolet light of this wavelength. The characteristics of this ultraviolet light are: short wavelength, high energy, and extremely destructive power. Strong, the energy of ultraviolet light in the 290nm~350nm band can reach 343~405KJ/mol. It is enough to cut the chemical bonds of organic matter and degrade macromolecules. Therefore, it is generally believed that ultraviolet rays in sunlight play a major role in the aging of plexiglass.

Under ultraviolet light, the inside of plexiglass undergoes chemical changes, and small molecular substances are produced. The carbon atoms on the main chain of plexiglass are connected to two side groups: α-CH3 and ester group -COOCH3, among which α-CH3 does not change much in the aging process, is relatively stable, and is not easy to break; while the ester group side bond is the easiest to follow The polymer breaks out to form small molecules. The main chain methylene group -CH2- also breaks, resulting in the decrease of the maximum molecular weight Mp and the weight average molecular weight Mw of the organic glass sample under the conditions of ultraviolet light aging. The use of GPC test method to test the molecular weight after aging also proves this point. That is to say, the scission of the methylene group on the main chain is the main factor in the decrease of the molecular weight of the organic glass, and it can be reflected by the change of the molecular weight.

Plexiglass will also produce thermal changes under the influence of different temperatures during use.

In addition, according to the kinetics of polymer decomposition reaction, under high temperature conditions, the molecular chain scission rate will increase, mainly because the side chain α-CH3 breaks, but the main chain generally does not break; temperature conditions coupled with ultraviolet light and oxygen will accelerate PMMA yellow The rate of change.

Plexiglass is a kind of polymer material. The aging phenomenon of polymer material caused by water is mainly affected by the effects of chemistry and physics.

Among them, the chemical action is mainly the hydrolysis of the molecular chain caused by water; the ester group in the plexiglass will undergo a hydrolysis reaction when encountering water, causing the main chain to break, resulting in a significant change in its performance.

The physical effect is that after the water is absorbed and penetrated into the polymer material, the force between the macromolecular chains is relatively reduced, and the mobility of the molecular chains is increased; in this way, the relative slippage between the molecular chains becomes Easy, resulting in a decline in the performance of polymer materials.

The above about the aging of acrylic, we are fully aware of it; then we will enter the main topic and delve into the reasons that affect the yellowing, and it will be much clearer.

One, innate factors-the purity of raw materials

The raw material of PMMA is methyl methacrylate, which usually has a purity of more than 99.9%, but only 0.1% of impurities have an important influence on the color of PMMA. If the purity of the raw material is too low, it contains more impurities and the risk of yellowing is greater. Among them, impurities such as high moisture content can cause defects such as bubbles in the finished plate formed by polymerization, and may also cause the light transmittance of the plate, which will lead to the increase of the haze of the plate and the decrease of transparency. When the impurity content is high, yellowing may occur during polymerization, and it will also aggravate the subsequent aging process. Therefore, controlling the purity of raw materials is not only the first step in the production of plexiglass, but also a very important step.

Raw material purity and impurity composition are the source of transparent acrylic yellowing; in this regard, Sunday Knight Co Ltd conducts a comprehensive inspection of raw materials through gas chromatography, analyzes the purity of raw materials, controls the content and types of impurities, and controls product quality from the source; in addition, through Carl The Fischer Moisture Tester performs moisture detection with a two-pronged approach to control quality from the source and put good quality first.

Second, the principle of light aging

The energy of ultraviolet rays is sufficient to cut the chemical bonds of organic substances, leading to a series of chain scission reactions, forming various products and functional groups. These functional groups, such as carbonyl groups, will become yellow after absorbing light. In addition, when multiple conjugated double bonds are formed, the absorption of the substance in the ultraviolet region will be red-shifted and begin to absorb blue-violet light, making the product appear yellow. .

Combining with the previous science about acrylic aging knowledge, we also understand that Acrylic Meichen will turn yellow due to ultraviolet light aging.

Sunday Knight Acrylic-Professional anti-aging and anti-yellowing solution:

The aging factors of PMMA core are known through the principle, so selective absorption of ultraviolet rays is the solution to PMMA yellowing. Sunday Knight is in accordance with the requirements for aging test in Chinese national standard GB/T 7134-2008 of plexiglass, referring to the standard GB/T 16422.1-1999 “Plastic Laboratory Light Source Exposure Test Method Part 1: General Rules” and GB/T 16422.2-1999 “Plastic Laboratory Light Source Exposure Test Method Part 2: Xenon Arc Lamp”, simulating the natural exposure environment and conducting a large number of experiments.

Our R&D team solves the problem of PMMA yellowing from multiple scales such as the raw material monomer impurity composition and content, UV absorption, PMMA molecular weight and molecular weight distribution, and residual monomer concentration.

In response to the problem of aging and yellowing, according to the different requirements of different customers, Sunday Knight has put forward a variety of solutions to prevent yellowing of PMMA sheets after a large number of verifications.

An acrylic with good anti-aging performance must have the quality of resistance to yellowing. At present, there are an endless stream of acrylic on the market; among them, the Sunday Knight acrylic has many types, high quality and good reputation; for the problem of acrylic yellowing, Sunday Knight also has mature and professional solutions.

2022-01-04