1. What is a polymer material processing aid? what is function?
Answer: Additives are various auxiliary chemicals that need to be added during production or processing of certain materials and products to improve production process, improve product performance, which needed in process of processing resin and raw rubber into plastic and rubber products.
Function: ①Improve process performance of polymers, optimize processing conditions, and submit processing efficiency; ②Improve performance of products, increase their use value and life.
2. What is compatibility of additives and polymers? What is meaning of sweating?
Answer: Spraying-precipitation of solid additives; sweating-precipitation of liquid additives.
Compatibility of additives and polymer refers to performance that additives and polymer can be uniformly mixed together for a long time without phase separation and precipitation;
3. What is role of plasticizer?
Answer: Weaken secondary bond between polymer molecules, that is, Van der Waals force, thereby increasing mobility of polymer molecular chains and reducing crystallinity of polymer molecular chains.
4. Why is polystyrene better than polypropylene in oxidation resistance?
Answer: Unstable H is replaced by a huge phenyl. Reason why PS is not easy to age is that benzene ring has a shielding effect on H; tertiary hydrogen in PP is easy to age.

 

5. What is reason why PVC is unstable when heated?
Answer: ①Molecular chain structure contains initiator residue and contains allyl chloride to act as an activating group. Terminal double bond reduces thermal stability; ②Influence of oxygen accelerates removal of HCL during thermal degradation of PVC; ③HCl produced by reaction has a catalytic effect on degradation of PVC; ④Influence of amount of plasticizer.
6. Based on current research results, what are main functions of heat stabilizers?
Answer: ①Absorb and neutralize HCL to inhibit its autocatalysis; ②Replace unstable allyl chloride atom in PVC molecule to inhibit removal of HCl; ③Addition reaction with polyene structure, destroying formation of large conjugated systems and reducing coloring; ④Capture free radicals and prevent oxidation reactions; ⑤Neutralize or passivate metal ions or other harmful substances that catalyze degradation; ⑥Protect, shield and weaken ultraviolet radiation.
7. Why UV rays are the most destructive to polymers?
Answer: Ultraviolet light has short wavelength and high energy, which breaks most of polymer chemical bonds.
8. What kind of synergistic system does intumescent flame retardants belong to, what are their basic principles and functions?
Answer: Intumescent flame retardants belong to phosphorus-nitrogen synergistic system.
Mechanism: When polymer containing flame retardant is heated, a uniform carbon foam layer can be formed on the surface, which has heat insulation, oxygen barrier, smoke suppression, and drip prevention, so it has good flame retardant properties.
9. What is oxygen index, what is relationship between oxygen index and flame retardancy?
Answer: OI=O2/(O2 N2)×100% where O2: oxygen flow rate; N2: nitrogen flow rate. Oxygen index refers to volume percentage of minimum oxygen necessary in nitrogen-oxygen mixed gas flow when a certain specification sample can continue to burn like a candle. OI<21 is flammable, OI 22-25 is self-extinguishing, 26-27 is flame-retardant, 28 or more is extremely flame-retardant.
10. How does antimony halogen flame retardant system have a synergistic effect?
Answer: Sb2O3 is commonly used for antimony, and organic halide is commonly used for halide. Sb2O3/machines are used together with halides, mainly because it interacts with hydrogen halides emitted by halides. And product is thermally decomposed into SbCl3, which is a volatile gas with a low boiling point. This gas has a high relative density and can stay in combustion zone for a long time to dilute combustible gas, isolate air, and play a role in inhibiting olefins; secondly, it can capture combustible free radicals to suppress flame. In addition, SbCl3 condenses into liquid drop-like solid particles above flame, its wall effect scatters a large amount of heat, which slows down or stops burning speed. Generally speaking, a ratio of 3:1 between chlorine and metal atoms is more appropriate.
11. According to current research, what are mechanism of action of flame retardants?
Answer: ①Decomposition products of flame retardant at burning temperature form a non-volatile and non-oxidized glass-like film, which can isolate reflected energy of air or have a low thermal conductivity.
②Flame retardant is decomposed by heat to generate incombustible gas to dilute combustible gas, dilute oxygen concentration in combustion zone;
③Flame retardant melts and decomposes to absorb heat and consume heat;
④Flame retardant promotes formation of a porous thermal insulation and stable carbon layer on plastic surface to prevent heat conduction and continue burning.
12. Why is plastic easily charged with static electricity during processing or use?
Answer: Since molecular chains of host polymer are almost composed of covalent bonds, they can neither ionize nor transfer electrons. In process of its processing and use of products, when it wants to contact and rub with other objects or itself, it will be charged due to gains and losses of electrons, and it is difficult to disappear through its own conduction.
13. What are characteristics of molecular structure of antistatic agents?
Answer: R—Y—X R: lipophilic group, Y: linking group, X: hydrophilic group. In their molecules, there should be a proper balance between lipophilic group of non-polar part and hydrophilic group of polar part, have a certain compatibility with polymer materials. Alkyl groups above C12 are typical lipophilic groups, while hydroxyl, carboxyl, sulfonic acid and ether bonds are typical hydrophilic groups.

 

14. Briefly describe mechanism of antistatic agent.
Answer: First, antistatic agent forms a conductive continuous film on the surface of material, that is, it can give surface of product a certain hygroscopic and ionic film, thereby reducing surface resistivity, causing electrostatic charge that has been generated to leak quickly to achieve purpose of antistatic; second is to give material surface a certain degree of lubricity, reduce coefficient of friction, thereby inhibiting and reducing generation of static charge.
①External antistatic agents generally use water, alcohol or other organic solvents as solvents or dispersants. When polymer material is impregnated with antistatic agents, lipophilic part of antistatic agent is firmly adsorbed on the surface of material, hydrophilic part outwards and absorbs moisture from air, thereby forming a conductive layer on the surface of material, which plays a role in eliminating static electricity;
②Internal antistatic agent is mixed into polymer matrix during plastic processing, and then migrates to polymer surface to play an antistatic effect;
③Polymer mixing type permanent antistatic agent is to blend hydrophilic polymer into polymer uniformly to form a conductive channel to conduct and release static charge.
15. After rubber is vulcanized, what changes usually happen to its structure and performance?
Answer: ①Vulcanized rubber changes from a linear to a three-position network structure; ②It no longer flows when heated; ③It no longer dissolves in its good solvent; ④Modulus and hardness are improved; ⑤Mechanical properties are improved; ⑥Aging resistance and chemical stability are improved; ⑦Media performance may decrease.
16. What is difference between sulfur vulcanization and sulfur donor vulcanization?
Answer: ①Sulfur vulcanization: multiple sulfur bonds, poor heat resistance and aging resistance, good flexibility, and large permanent deformation; ②Sulfur donor: many single sulfur bonds, good heat resistance and aging resistance.
17. What role does vulcanization accelerator play?
Answer: A substance that improves production efficiency of rubber products, reduces costs, improves performance, and can promote vulcanization. It can shorten vulcanization time, lower vulcanization temperature, reduce amount of vulcanizing agent, improve physical and mechanical properties of rubber.
18. Scorch phenomenon: refers to early vulcanization of rubber compound during processing.
19. Briefly describe role and main varieties of vulcanizing active agents
Answer: Role of active agent-enhance activity of accelerator, reduce amount of accelerator, and shorten curing time.
Active agent: a substance that can increase activity of organic accelerator and make it fully effective, thereby reducing amount of accelerator or shortening curing time. Active agents are generally divided into inorganic active agents and organic active agents. Inorganic active agents mainly include metal oxides, hydroxides and basic carbonates; organic active agents mainly include fatty acids, amines, soaps, polyols and amino alcohols. Only a small amount of active agent can be added to rubber compound to increase its degree of vulcanization.
1) Inorganic active agent: mainly metal oxide;
2) Organic active agents: mainly fatty acids.
Note: ①ZnO can be used as a metal oxide vulcanizing agent to crosslink halogenated rubber; ②ZnO can improve heat resistance of vulcanized rubber.
20. What is after-effect of an accelerator, and what kind of accelerator has a good after-effect?
Answer: Below vulcanization temperature, it will not cause early vulcanization; when vulcanization temperature is reached, vulcanization activity is large. This property is called after-effect of accelerator. Sulfonamides have good after effects.
21. Definition of lubricant and difference between internal and external lubricants?
Answer: Lubricant-can improve friction and adhesion between particles of each layer of plastic, melt and metal surface of processing equipment, increase fluidity of resin, achieve controllable resin plasticization time, and maintain auxiliary agent of continuous production, which is called lubricant.
External lubricants can increase lubricity of plastic surface during processing, reduce adhesion between plastic and metal surface, minimize mechanical shearing force, so as to achieve purpose of the easiest processing and forming without damaging properties of plastic. Internal lubricants can reduce internal friction of polymer, increase melting rate and melt deformation of plastic, reduce melt viscosity and improve plasticizing performance.
Difference between internal and external lubricants: internal lubricants are required to have good compatibility with polymers, reduce friction between molecular chains, and improve fluidity; while external lubricants require certain compatibility with polymers to reduce friction between polymer and surface of processing machinery.
22. What are factors that determine size of filler reinforcement?
Answer: Size of reinforcement depends on body structure of plastic itself, amount of filling particles, specific surface and size, surface activity, particle size and distribution, phase structure, particle aggregation and dispersion in polymer. The most important of these is interaction between filler and interface layer formed by polymer chain. This effect includes not only physical or chemical force of particle surface on polymer chain, but also crystallization and orientation of polymer chain in interface layer.
23. What factors affect strength of reinforced plastics?
Answer: ①Strength of reinforcing agent can be selected to meet requirements; ②Strength of basic polymer can be satisfied by selection and modification of polymer; ③Surface cementation of plasticizer and basic polymer; ④Structure of reinforcing material material.
24. What is a coupling agent, its molecular structure characteristics, and examples to illustrate mechanism of action.
Answer: Coupling agent refers to a class of substances that can improve interface characteristics between fillers and polymer materials.
There are two functional groups in its molecular structure: one can react chemically with polymer matrix or at least have good compatibility; the other can form chemical bonds with inorganic fillers, such as: silane coupling agent, general formula can be written as RSiX3, where R is an active functional group that has affinity and reactivity with polymer molecules, such as vinyl chloropropyl, epoxy, methacryl, amine and mercapto groups. X is a hydrolyzable alkoxy group, such as methoxy group, ethoxy group, etc.
25. What is a foaming agent?
Answer: Blowing agent is a kind of substance that can make rubber and plastic in a liquid or plastic state within a certain viscosity range form a microporous structure.
Physical foaming agent: a type of compound that relies on change of its physical state during foaming process to achieve foaming goal;
Chemical foaming agent: It will thermally decompose at a certain temperature to produce one or more kinds of gases to make polymer foam.
26. What are characteristics of inorganic chemistry and organic chemistry foaming agents when they decompose?
Answer: Advantages and disadvantages of organic foaming agents: ①Good dispersibility in polymers; ②Narrow decomposition temperature range, easy to control; ③N2 gas produced does not burn, explode, and is not easy to liquefy. It has a low diffusion rate and is not easy to escape from foam, so rate of robes is high; ④Particles are small, cells of foam are small; ⑤There are more varieties; ⑥There are more residues after foaming, sometimes as high as 70%-85%. These residues sometimes cause odor, pollute polymer materials or produce surface blooming phenomenon; ⑦Decomposition is generally an exothermic reaction. If decomposition heat of foaming agent used is too high, it may cause a large temperature gradient inside and outside foaming system during foaming process, sometimes cause internal temperature to be too high, damage physical and chemical properties of polymer. ⑧Organic foaming agents are mostly flammable materials, so they should be fireproof during storage and use.
27. What is a masterbatch?
Answer: It is an aggregate prepared by uniformly loading an ultra-constant amount of pigment or dye in the resin; basic composition: pigment or dye, carrier, dispersant, additive;
Function: ①It is beneficial to maintain chemical stability of pigment and stability of color; ②make pigments have better dispersion in plastic; ③protect health of operators; ④simple process, easy to change color; ⑤clean environment, no staining of utensils; ⑥save time and raw materials.
28. What is tinting strength?
Answer: It is ability of colorant to affect color of entire mixture with its own color; when colorant is used in plastic products,meaning of hiding power refers to its ability to prevent light from penetrating product.