28 questions about plastic processing additives

November 19, 2019

28 questions about plastic processing additives
 

1. What is a polymer processing aid? what is the function?
A: Auxiliaries are various auxiliary chemicals that need to be added during the production or processing of certain materials and products to improve the production process and improve product performance. In the process of processing resins and raw rubber into plastics and rubber products. A variety of auxiliary chemicals needed.


Function: 1 Improve the process performance of the polymer, optimize the processing conditions, and submit the processing efficiency; 2 Improve the performance of the products, improve their use value and longevity.

 

2. What is the compatibility of the additive with the polymer? What is the meaning of squirting and sweating?
Answer: Spraying - precipitation of solid additives; sweating - precipitation of liquid additives.

The compatibility of the auxiliary agent and the polymer means that the auxiliary agent and the polymer can be uniformly mixed for a long time, and the properties of phase separation are not produced;

 

3. What is the role of plasticizer?
A: The weaker bond between the polymer molecules, van der Waals force, is weakened, thereby increasing the mobility of the polymer molecular chain and reducing the crystallinity of the polymer molecular chain.

 

4. Why is polystyrene better resistant to oxidation than polypropylene?
Answer: Unstable H is replaced by a large phenyl group. The reason why PS is not easy to age is that benzene ring has a shielding effect on H; PP contains tert-hydrogen and is easy to age.

 

5. What is the cause of PVC instability?
Answer: 1 The molecular chain structure contains the initiator residue containing allyl chloride to act as an activating group. The terminal double bond reduces the thermal stability; 2 the effect of oxygen accelerates the de-HCL when the thermal degradation of PVC occurs; 3 The HCl produced by the reaction has a catalytic effect on the degradation of PVC; 4 the influence of the amount of plasticizer.

 

6. Based on the current research results, what are the main effects of heat stabilizers?
Answer: 1 absorbs and neutralizes HCL, inhibits its autocatalysis; 2 replaces the unstable allyl chloride atom in PVC molecule, inhibits the detachment of HCl; 3, the addition reaction with polyene structure destroys the formation of large conjugated system , reduce coloration; 4 capture free radicals, prevent oxidation reaction; 5 neutralize or passivate metal ions or other harmful substances that catalyze degradation; 6 protect, shield and attenuate ultraviolet radiation.

 

7. Why is ultraviolet light most destructive to polymers?
A: The ultraviolet wavelength is short and the energy is large, which interrupts most of the polymer chemical bonds.

 

8. Which type of synergistic system does the intumescent flame retardant belong to? What is the basic principle?
Answer: Intumescent flame retardant belongs to the phosphorus-nitrogen synergistic system.
Mechanism: When the polymer containing the flame retardant is heated, the surface can form a uniform layer of carbon foam, which has good flame retardant properties, such as heat insulation, oxygen barrier, smoke suppression and drip prevention.

 

9. What is the oxygen index, and what is the relationship between the oxygen index and the flame retardancy?
Answer: OI=O2/(O2 N2)×100%, O2: oxygen flow rate; N2: nitrogen flow rate. Oxygen index refers to the volume percentage of the minimum oxygen required in a nitrogen-oxygen mixed gas stream when a sample of a certain specification is like a candle. OI<21 is flammable, OI is 22 to 25 self-extinguishing, 26 to 27 is flame retardant, and 28 or more is extremely flame retardant.

 

10. How does the halogen flame retardant system synergize?
A: Sb2O3 is commonly used, and halides are commonly used as organic halides. The Sb2O3/machine is used with a halide, mainly because it interacts with the hydrogen halide evolved from the halide.

And the product is thermally decomposed into SbCl3, which is a volatile gas with a relatively low boiling point. The gas has a relatively high density and can stay in the combustion zone for a long time to dilute the flammable gas, insulate the air, and act as a hindrance; secondly, it It can capture flammable free radicals to suppress the action of flame. In addition, SbCl3 condenses into droplet solid particles over the flame, and its wall effect scatters a large amount of heat, slowing down or stopping the burning speed. In general, chlorine and metal atoms are more suitable for 3:1.

 

11. According to the current research, what are the mechanisms of action of flame retardants?
Answer: 1 The decomposition product of the flame retardant at the combustion temperature forms a non-volatile non-oxidized glassy film, which can block the air reflection energy or have a low thermal conductivity.
2 The flame retardant is thermally decomposed to generate non-combustion gas to dilute the flammable gas, dilute the concentration of oxygen in the combustion zone; 3 the flame retardant dissolves and decomposes the heat absorbed heat;
4 Flame retardant promotes the formation of a porous insulating and stable carbon layer on the plastic surface to prevent heat conduction and continue combustion.

 

12. Why is plastic easily electrostatically charged during processing or use?
Answer: Because the molecular chains of the main polymer are almost all composed of covalent bonds, they can neither ionize nor transfer electrons. During the processing and use of the product, when it is in contact with and rubbed with other objects or itself, it is charged due to the gain and loss of electrons, and it is difficult to disappear by self conduction.

 

13. What are the characteristics of the molecular structure of antistatic agents?
A: R-Y-X R: lipophilic group, Y: linking group, X: hydrophilic group. In their molecules, the oleophilic group of the non-polar moiety and the hydrophilic group of the polar moiety should have an appropriate balance, which has certain compatibility with the polymer material, and the alkyl group of C12 or higher is a typical lipophilic group. The hydroxy group, the carboxyl group, the sulfonic acid group and the ether bond are typical hydrophilic groups.

 

14. Briefly describe the mechanism of action of antistatic agents.
Answer: First, the antistatic agent forms a conductive continuous film on the surface of the material, which can impart a certain hygroscopicity and ionicity to the surface of the product, thereby reducing the surface resistivity and rapidly leaking the static charge that has been generated to achieve resistance. The purpose of static electricity; the second is to give the surface of the material a certain degree of lubricity, reduce the friction coefficient, thereby inhibiting and reducing the generation of static charge.

1 The external antistatic agent is generally used as a solvent or dispersant with water, alcohol or other organic solvent. When the polymer material is impregnated with the antistatic agent, the lipophilic portion of the antistatic agent is firmly adsorbed on the surface of the material, and the hydrophilic portion is oriented. Externally absorbing moisture from the air to form a conductive layer on the surface of the material to eliminate static electricity;
2 The antistatic agent is mixed into the polymer matrix during processing of the plastic, and then migrates to the surface of the polymer to exert an antistatic effect;
3 Polymer-mixed permanent antistatic agent is a kind of hydrophilic polymer uniformly blended into the polymer to form a conductive channel, conducting and releasing static charge.

 

15. What is the usual change in structure and properties of rubber after vulcanization?
Answer: 1 vulcanized rubber changes from linear to three-position network structure; 2 heating no longer flows; 3 is no longer soluble in its good solvent; 4 modulus and hardness increase; 5 mechanical properties improve; 6 aging resistance and Chemical stability is improved; 7 media properties may be degraded.

 

16. What is the difference between sulfur vulcanization and sulfur vulcanization?
Answer: 1 sulfur vulcanization: polysulfide bond, heat resistance, poor aging resistance, good flexibility and permanent deformation; 2 sulfur donor: single sulfur bond, heat resistance, good aging resistance.

 

17. What is the role of the vulcanization accelerator?
A: Improve the production efficiency of rubber products, reduce costs and improve performance. A substance that promotes vulcanization. It can shorten the curing time, reduce the vulcanization temperature, reduce the amount of vulcanizing agent and improve the physical and mechanical properties of rubber.

 

18. Scorch phenomenon: refers to the phenomenon of early vulcanization of rubber rubber during processing.

 

19. Briefly describe the role and main varieties of vulcanization active agents
A: The role of the active agent - to enhance the activity of the accelerator, reduce the amount of accelerator, and shorten the curing time.
Active agent: A substance that increases the activity of an organic promoter to maximize its effectiveness, thereby reducing the amount of accelerator or shortening the curing time. Active agents are generally classified into two types: inorganic active agents and organic active agents. The inorganic active agent mainly includes metal oxides, hydroxides and basic carbonates; the organic active agents mainly include fatty acids, amines, soaps, polyols and amino alcohols. The degree of sulfidation can be increased by adding the active agent to the rubber compound in a small amount.

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 the heat resistance of vulcanized rubber.

 

20. What is the post-effect of the accelerator, and what kind of accelerator has a good aftereffect?
Answer: Below the vulcanization temperature, the vulcanization activity is not caused when the early vulcanization reaches the vulcanization temperature. This property is called the post-effect of the accelerator. The sulfenamides have good after effects.

 

21. What is the definition of lubricant and the difference between internal and external lubricants?
A: Lubricant - can improve the friction and adhesion between the particles of the plastic layer and the metal surface of the melt and processing equipment, increase the fluidity of the resin, achieve the plasticization time of the resin, and maintain the continuous production. The agent is called a lubricant.

The external lubricant can increase the lubricity of the plastic surface during processing, reduce the adhesion of the plastic to the metal surface, and minimize the mechanical shearing force, thereby achieving the easiest processing without damaging the plastic properties. purpose. The internal lubricant can reduce the internal friction of the polymer, increase the melting rate and melt deformability of the plastic, reduce the melt viscosity and improve the plasticizing performance.

The difference between internal and external lubricants: internal lubricants require better compatibility with polymers, reduce friction between molecular chains, and improve flow properties; while external lubricants require certain compatibility with polymers, reducing polymers Friction with the surface of the processing machine.

 

22. The size of the reinforcing effect of the filler depends on the factors?
Answer: The size of the reinforcing effect depends on the bulk structure of the plastic itself, the amount of filler particles, specific surface and size, surface activity, particle size and distribution, phase structure and particle dispersion and dispersion in the polymer. The most important of these is the interaction of the filler with the interfacial layer formed by the polymer polymer chain. This action includes both the physical or chemical interaction of the particle surface with the polymer chain and the crystallization of the polymer chain in the interfacial layer. Orientation, etc.

 

23. What factors affect the strength of reinforced plastics?
Answer: 1 The strength of the reinforcing agent is selected to meet the requirements; 2 The strength of the basic polymer can be satisfied by the selection and modification of the polymer; 3 The surface cementation of the plasticizer and the base polymer; 4 The structure of the reinforcing material material.

 

24. What is a coupling agent, its molecular structural characteristics, and an example of the mechanism of action.
Answer: Coupling agent refers to a class of substances that improve the interfacial properties between the filler and the polymer material.

There are two functional groups in the molecular structure: one can chemically react with the polymer matrix or at least have good compatibility; the other can form a chemical bond with the inorganic filler. For example: silane coupling agent, the general formula can be written as RSiX3, where R is a reactive functional group having affinity and reaction ability with polymer molecules, such as vinyl chloropropyl group, epoxy group, methacryl group, amine group and sulfhydryl group. Wait. X is a hydrolyzable alkoxy group such as a methoxy group, an ethoxy group or the like.

 

25. What is a foaming agent?
Answer: A foaming agent is a kind of rubber that can make a microporous structure in a liquid or plastic state in a certain viscosity range.
Physical foaming agent: a type of compound that relies on changes in its physical state during foaming to achieve foaming purposes;
Chemical blowing agent: It will thermally decompose at a certain temperature to produce one or more gases to foam the polymer.

 

26. What are the characteristics of inorganic chemical and organic chemical foaming agents?
Answer: Advantages and disadvantages of organic foaming agent: 1 good dispersibility in polymer; 2 decomposition temperature range is narrow, easy to control; 3 N2 gas produced does not burn, does not explode, is not easy to liquefy, and has low diffusion speed, not easy It escapes from the foam, so the robes are high; 4 particles are small, the cells of the foam are small; 5 varieties are more; 6 the residue after foaming is more, sometimes as high as 70%-85%, sometimes these residues It will cause strange odor, polluting the polymer material or causing surface blooming; 7 decomposition is generally an exothermic reaction. If the decomposition agent used is too hot, it may cause foaming system inside and outside during the foaming process. Large temperature gradients sometimes cause the internal temperature to be too high to damage the physicochemical properties of the polymer. 8 organic foaming agents are mostly flammable materials, should pay attention to fire prevention during storage and use.

 

27. What is masterbatch?
A: It is an aggregate obtained by uniformly loading a super-constant pigment or dye into a resin; basic composition: pigment or dye, carrier, dispersant, additive; role: 1 is beneficial to keep the chemical stability of the pigment Stability of color and color; 2 makes the pigment have better dispersibility in plastic; 3 protects the health of the operator; 4 is simple in process, easy to change color; 5 clean environment, non-staining vessel; 6 saving time and raw materials.

28. What does tinting strength mean?
A: The ability of a colorant to affect the color of the entire mixture in its own color; when used in a plastic article, hiding power means the ability to block light from penetrating the article.

 

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