【Popular Science on Polymers and Materials】--A detailed explanation of the functions of additives in polymer materials; worth sharing as popular science content +ljtjbx
Thread Content
This post was last edited by ljtjbx on 2015-11-23 at 10:17. Additives for polymer materials are substances that can improve the properties of these materials, assist in their processing, or endow them with new properties; they are important functional components of polymer materials, also known as additives. High-volume additives, which are important components of the product matrix and have a significant impact on the product’s shape, structure, and performance, are generally not classified as additives. 1. Plasticizers ； This is the additive most commonly heard of in the plastics industry; the plasticizer scandal in Taiwan from a few years ago still seems fresh in people’s minds. Plastic, literally speaking, is a material that can be shaped, and plasticizers can be understood as substances that increase the malleability of plastic. The main component of plastics is polymers, without exception ； The basic concept of polymers is that they have an extremely high molecular weight; from a microscopic perspective, this means they possess very long molecular chains, with their most basic shape resembling that of a centipede. On a macro level, to avoid agoraphobia, one can imagine what it’s like to have thousands of centipedes wrapping around oneself (it’s like the brain is about to explode; let’s take a break from that idea for now, and use the analogy of braids instead, ignoring the side chains) ； If the braids are twisted too tightly, they become less likely to deform. Therefore, to turn a braid into a double ponytail, it’s necessary to loosen the braids slightly first. The most common method for polymers is heating them up and then tying the braids back together again – that is, setting their shape, using methods such as blow molding or extrusion. However, polymers have varying properties; some of them tend to degrade easily during the process of being \"decomposed.\" PVC is a prime example – it needs to be heated to 170 degrees in order to be processed, but at 140 degrees it already starts releasing hydrogen chloride, which is hydrochloric acid gas, and this poses quite a problem. Let’s think about it: what would happen if our hair got tangled together after sleeping and couldn’t be untangled? Some people might wear it as a new hairstyle, but most would choose to wash their hair. So scientists came up with this solution as well: by adding plasticizers to PVC, it can be processed at 140 degrees Celsius. Choosing plasticizers is also a matter of expertise; just as it’s not possible to wash one’s hair with sesame oil, most of the plasticizers used in PVC are phthalates, including the widely criticized DEHP. Since we are discussing functions, we will not go into further detail on health topics here. It should be noted that since plasticizers tend to precipitate easily, which affects product quality, even if they do not precipitate, the strength of the plastic is reduced. As a result, plastic processing companies strive to use as little plasticizer as possible. In terms of usage volume, plasticizers used in PVC and PVDC account for over 90% of the total amount used in the plasticizer industry, which further confirms this point. Therefore, the claim that \"all plastics contain plasticizers\" should be viewed with skepticism. 2. Toughening agents are easily confused with plasticizers; indeed, some plasticizers can also be used as toughening agents, as both generally work by altering the crystallinity of polymers. But in terms of product specifications, the two are actually different. Using hair as an analogy again, plasticizers are like water; they play a role mainly during the processing stage, while toughening agents are like conditioners, serving primarily during the subsequent application phase. Some plastics are very brittle; they behave like glass when in use, breaking upon falling to the ground. Clearly, this makes them unsuitable for practical use. After all, many people prefer plastic products precisely because they are less likely to break. The role of the toughening agent is to solve this problem. For PVC plastic, plasticizers also serve as toughening agents, but the toughening agents for other plastics are diverse; in some cases, polymers such as rubber are used directly as toughening agents. 3. Antioxidants: If you are concerned about the health aspects of instant noodle products, you have probably heard of a substance called BHT; it was mentioned in news reports a few years ago. BHT is the most common phenolic antioxidant, widely used in the plastics industry, and it is practically essential in the material processing sector. Plastics are organic polymers, and their molecules are actually quite fragile. It’s dangerous for them to come into contact with substances like oxygen at high temperatures, just as it would be dangerous for a young girl wearing simple clothing to walk on a quiet street late at night. We all know that oxygen is the culprit behind certain things that shouldn’t happen; it has nothing to do with the polymers themselves. But oxygen is extremely powerful, and the Earth can’t do without it. So, we have to give the polymers more \"clothing\", in other words, antioxidants. When they encounter oxygen, these antioxidants act like a coat that protects the polymers, allowing them to avoid more serious consequences. This is essentially the function of antioxidants. 4. Flame retardants: Flame retardants are not widely used in the plastics industry, but they are indeed very important. If the plastics processing industry were to produce flame-retardant plastics in accordance with standards, the hazards caused by many fires could be reduced. So, let me add one more personal observation: in China’s plastic processing industry, the problems related to additives are not only excessive use, but also incorrect use and insufficient use; the latter two issues are even more serious. The protective benefits of additives for us far outweigh any potential harms. The function of flame retardants is simple: they slow down the rate of combustion. Many of them are substances containing phosphorus or chlorine, which generate free radicals rapidly thereby preventing the spread of the fire.
This post was last edited by ljtjbx on 2015-11-23 at 10:19. 5. Colorants are even simpler: they serve to color plastics. However, one should not take the issue of coloring lightly; performance and aesthetics are the two most important aspects in plastic processing. Performance determines the application of a product, while aesthetics determine its profitability. Therefore, for specific companies, the latter is sometimes given even more attention. If we see a smartphone with uneven coloring on its casing, it’s likely that we won’t buy it. As for its resistance to drops, well, even at the counters of those brands known for their \"nut-cracking\" devices, I’ve never seen anyone test the strength of the casing when purchasing a phone. There are many different terms used to refer to colorants: pigments, color fillers, dyes, color pastes, masterbatches, etc. Fortunately, each of these terms has a different meaning – so students majoring in polymer science, how’s your memory? I won’t go into details here. 6. Reinforcers (strengthening agents): What is commonly referred to as a filler in everyday language is usually also an enhancer, and its function is to increase the strength of plastics. Strength is different from hardness, and this distinction is important to keep in mind. Hardness is not required in most applications for plastics, but strength is generally a significant requirement for plastics, except at the tear points of food bags. Most of the time, reinforcing agents can also reduce the cost of plastics, as the commonly used ones, including calcium carbonate, talc, graphite or carbon black, as well as silica, are relatively inexpensive. Of course, these substances can be enhanced through their direct interaction with polymers; they cannot be added in unlimited quantities, as excessive addition will also lead to a decrease in strength. They are generally also harmless. 7. Crosslinking agents: Crosslinking agents can also be referred to as reinforcing agents, as they have a similar effect on the finally formed material. But unlike ordinary fillers, a chemical reaction occurs between the crosslinking agent and the polymer. Through chemical reactions such as cross-linking, the shaping of plastics becomes more stable. Using the hair from earlier as an example, the usual way to hold it in place is by tying it with a hair tie; this tie might come loose when running, whereas a crosslinking agent acts like a clip, providing a stronger hold. 8. Light stabilizers: Ultraviolet light, a type of high-energy electromagnetic wave, can cause chain breaks in many polymers; light stabilizers are used to address this issue. 9. The heat stabilizer is similar to Article 8, except that the energy source for the chain-scission reaction becomes high temperature. 10. Foaming agents: Have you eaten instant noodles? How do the noodles expand when soaked? Of course, it’s not thanks to the blowing agent. What is being discussed here are instant noodle containers – how does this type of foam plastic come about? Most plastics are solid; to create foam plastic similar to steamed buns, yeast obviously cannot be used, as it is unlikely to survive within the plastic processing process. Thus, blowing agents take on the role of yeast in this regard. Of course, there are various mechanisms for foaming, and common foaming gases include carbon dioxide, nitrogen, ammonia, and others. It would take a whole book to describe the foaming process in detail. 11. Lubricants are also primarily used during the processing stage, and they are somewhat similar to plasticizers – plasticizers reduce friction between molecules, while lubricants can not only reduce friction between molecules but also reduce friction between molecules and the container. 12. Antistatic agents and flame retardants can be seen as analogous to each other; they are used in relatively small quantities, but they are extremely important in specific situations, especially in electronic components, where their role is to reduce static electricity buildup on the surface of plastics. 13. There are many more. The additives mentioned above are those that are commonly used in the plastic processing process. Some special types of plastics require special additives as well; for example, in the case of fluoroplastics, many additives cannot be used with them. Moreover, the additives used in the fluoroplastic industry are generally not utilized in common plastics.
Plasticizers are used to make polymers more fluid; as the name suggests, they increase the plasticity of polymers, thereby facilitating processing. Various other catalyst inhibitors and protectants (antioxidants) are used to protect polymers from premature aging. Vulcanization accelerators, used to accelerate the vulcanization of rubber and promote its cross-linking. Fillers & reinforcing agents, such as carbon black and calcium carbonate, white carbon black, which are used to increase strength (especially in rubber) and reduce costs. Pigments and blowing agents, which produce CO2 and are used in foams