Common problems of plastic processing aids
1. What is polymer processing aid? What is its role?
A: Additives are various auxiliary chemicals that need to be added in the production or processing process of certain materials and products to improve the production process and production performance, and various auxiliary chemicals needed in the process of processing resin and raw rubber into plastic and rubber products.
Functions: (1) Improve the processing performance of polymer, optimize processing conditions and improve processing efficiency; (2) Improve the performance of products and improve their service value and life.
2. What is the compatibility of additives and polymers? What is the meaning of sweating?
Answer: spray polymerization - precipitation of solid additives; Sweating - the precipitation of liquid additives. The compatibility of additives and polymers refers to the performance that additives and polymers can be mixed uniformly and together for a long time without producing phase separation and precipitation.
3. What is the function of plasticizer?
Answer: It weakens the covalent bond between polymer molecules, that is, van der Waals force, thus increasing the mobility of polymer molecular chain and reducing the crystallinity of polymer molecular chain.
4. Why does polystyrene have better oxidation resistance than polypropylene?
Answer: The unstable H is replaced by the huge phenyl. The reason why PS is not easy to age is that the benzene ring has a shielding effect on H; PP contains tertiary hydrogen which is easy to age.
5. What is the reason for the unstable heating of PVC?
Answer: ① The molecular chain structure contains initiator residue and allyl chloride, which plays the role of activating group. The terminal double bond reduces the thermal stability; ② The influence of oxygen accelerates the removal of HCL during the thermal degradation of PVC; ③ The HCl produced by the reaction has catalytic effect on the degradation of PVC; ④ The effect of plasticizer dosage.
6. According to the current research results, what are the main functions of heat stabilizers?
Answer: ① Absorb and neutralize HCL and inhibit its autocatalysis; ② Displace the unstable allyl chloride atom in the PVC molecule, and inhibit the removal of HCl; ③ Addition reaction with polyene structure will destroy the formation of large conjugated system and reduce coloration; ④ Capture free radicals and prevent oxidation reaction; ⑤ Neutralize or passivate metal ions or other harmful substances that catalyze degradation; ⑥ It can protect, shield and weaken ultraviolet radiation.
7. Why is UV the most destructive to polymers?
A: The ultraviolet wave is long and powerful, which breaks most of the chemical bonds of polymers.
8. What kind of synergistic system does intumescent flame retardant belong to and what is its basic principle and function?
A: The intumescent flame retardant belongs to the phosphorus-nitrogen synergistic system.
Mechanism: When the polymer containing the flame retardant is heated, a uniform layer of carbon foam can be formed on its surface. The layer has good flame retardancy because of its heat insulation, oxygen isolation, smoke suppression and drip prevention.
9. What is the oxygen index and what is the relationship between the oxygen index and flame retardance?
Answer: OI=O2/(O2+N2) × In the formula of 100%, O2: oxygen flow; N2: nitrogen flow. Oxygen index refers to the volume percentage of the lowest oxygen required in the nitrogen-oxygen mixture flow when the sample of a certain specification can burn continuously and stably like a candle. OI<21 is flammable, OI of 22~25 is self-extinguishing, 26~27 is flame retardant, and above 28 is extremely flame retardant.
10. How does antimony halide flame retardant system have synergistic effect?
Answer: Sb2O3 is commonly used for antimony, and organic halides are commonly used for halides. Sb2O3/machine is used with halides, mainly because of its interaction with hydrogen halide released by halides. The product is thermally decomposed into SbCl3, which is a volatile gas with a low boiling point. The relative density of this gas is high, and it can stay in the combustion zone for a long time to dilute the combustible gas, isolate the air, and act as an olefin inhibitor; Secondly, it can capture combustible free radicals to inhibit flame. In addition, SbCl3 condenses into droplets of solid particles over the flame, and its wall effect scatters a large amount of heat, slowing down or stopping the combustion speed. Generally, 3:1 is more suitable for chlorine and metal atoms.
11. According to the current research, what are the action mechanisms of flame retardants?
Answer: ① The decomposition products of the flame retardant at the combustion temperature form a non-volatile and non-oxidizing glass-like film, which can isolate the reflected energy of the air or has a low thermal conductivity.
② The flame retardant is decomposed into incombustible gas by heat to dilute the combustible gas and dilute the oxygen concentration in the combustion zone; ③ Heat consumption due to heat absorption of flame retardant dissolution and decomposition;
④ The flame retardant promotes the formation of a porous thermal insulation layer on the plastic surface to prevent heat conduction and continuous combustion.
12. Why is plastic easy to carry static electricity during processing or use?
A: Because the molecular chain of its main polymer is almost composed of covalent bonds, it can neither ionize nor transfer electrons. In the process of its processing and use of products, when it wants to contact and rub with other objects or itself, it will be electrified due to the gain and loss of electrons, and it is difficult to disappear through its own conduction.
13. What are the characteristics of the molecular structure of antistatic agents?
Answer: R-Y-X R: lipophilic group, Y: connecting group, X: hydrophilic group. In their molecules, there should be an appropriate balance between the lipophilic group of the non-polar part and the hydrophilic group of the polar part, and have a certain compatibility with the polymer materials. Alkyl groups above C12 are typical lipophilic groups, while hydroxyl, carboxyl, sulfonic and ether bonds are typical hydrophilic groups.
14. Briefly describe the action mechanism of antistatic agent.
Answer: First, the antistatic agent forms a continuous film of conductivity on the surface of the material, that is, it can endow the surface of the product with a certain moisture absorption and ionic film, thus reducing the surface resistivity, so that the generated static charge can leak quickly, so as to achieve the purpose of antistatic; The second is to endow the material surface with certain lubricity, reduce the friction coefficient, and thus inhibit and reduce the generation of static charges.
① The external antistatic agent is generally used with water, alcohol or other organic solvents as solvent or dispersant. When the antistatic agent is used to impregnate the polymer material, the hydrophilic part of the antistatic agent is firmly adsorbed on the surface of the material, and the hydrophilic part is outward and absorbs water from the air, thus forming a conductive layer on the surface of the material, which plays the role of eliminating static electricity;
② The internal antistatic agent is mixed into the polymer matrix during plastic processing, and then transferred to the polymer surface to play an antistatic role;
③ The permanent antistatic agent of polymer mixing type is to uniformly blend hydrophilic polymer into the polymer to form a conductive channel to conduct and release static charges.
15. Structure and properties of rubber after vulcanization