CN112630262B

CN112630262B - Test method for detecting activity of vulcanization activator

Info

Publication number: CN112630262B
Application number: CN202011529931.2A
Authority: CN
Inventors: 姜海波; 李春忠; 侍槟; 周鹰杰; 王博慧; 柳坤鹏; 胡金能
Original assignee: East China University of Science and Technology
Current assignee: East China University of Science and Technology
Priority date: 2020-12-22
Filing date: 2020-12-22
Publication date: 2023-12-22
Anticipated expiration: 2040-12-22
Also published as: CN112630262A

Abstract

The invention discloses a test method for detecting the activity of a vulcanization activator, which comprises the following steps: and (3) performing differential scanning calorimetry test on the mixture of the to-be-detected vulcanization active agent and the sulfenamide accelerator to obtain the maximum exothermic peak temperature of the mixture. The testing method does not need the steps of mixing, vulcanizing and the like, has wide screening range of the vulcanizing active agent, and can realize the testing of the activity of different types of vulcanizing active agents by using a differential scanning calorimeter.

Description

Test method for detecting activity of vulcanization activator

Technical Field

The invention relates to the field of rubber, in particular to a test method for detecting the activity of a vulcanization activator.

Background

Zinc oxide (ZnO) is widely used as an additive in various materials and products, mainly as an active agent for the rubber industry. The addition of ZnO can accelerate vulcanization kinetics, reduce energy consumption of vulcanization and improve physical properties of vulcanized rubber. Although the application of ZnO in rubber has a long history and its addition has a great improvement in rubber properties, its mechanism of action in vulcanization is not quite clear.

ZnO exists in the form of ores in the natural environment, but artificial mining has resulted in concentrations that far exceed natural concentrations in certain areas. For example, during wear and discard of automobile tires, a large amount of ZnO which does not participate in vulcanization flows into rivers, so that local water resources are polluted. Numerous studies have considered ZnO to be highly toxic to aquatic organisms and this hazard is irreversible. In some european rivers, the zinc content is well above the level that is environmentally friendly. Although zinc is an essential dietary element necessary for the human body, inhalation of excessive amounts of ZnO fumes can also adversely affect the health of the human body. Recent studies have shown that inhalation of ZnO particles damages the lungs and can have long-term adverse effects on health. ZnO particles generated during rubber tire wear are considered to be the main cause of this pollution, which results in nearly ten thousand tons of ZnO pollution in the last century in the united states alone each year, and this figure is also growing exponentially. It is therefore considered necessary to reduce the amount of ZnO in rubber tires. The European Union and California of the United states have listed ZnO as an environmentally hazardous chemical and have put down relevant legal regulations to reduce the use of ZnO in the rubber industry, which has led many scholars to work in searching for ZnO substitutes.

Hassalutai et al used fly ash as a raw material to prepare a Geopolymer to replace ZnO in natural rubber, and the properties of the vulcanized natural rubber can meet the previous requirements (Hassarutai Yangthong, skulrat Pichaiyut, suwaluk Wisunthorn, norbert Vennemann, charoen Nakason. J.appl. Polym, sci.2019, 48624.) and the whole experimental process comprises the whole process of rubber mixing and vulcanization, which is time-consuming and labor-consuming.

Yulia Glebova et al innovatively used nitrogen-doped graphene instead of ZnO as a rubber vulcanization activator, providing a new idea for the preparation of the activator (Yulia Glebova, nikolai Severin, vladimir Shershnev, j.appl. Polym, sci.2017, 46116.) and the selection process involved all processes in the rubber preparation process. In the prior art, a series of procedures such as rubber mixing, vulcanization and testing are necessary for screening vulcanization active agents. The screening step is tedious, energy-consuming and high cost.

Chinese patent document CN105842277a discloses a test method for detecting the activity of a vulcanization activator, which is to mix and grind an organic thiosulfate sample, a vulcanization activator and squalene, and then test the mixture by a differential scanning calorimeter, wherein the lower the temperature is, the better the activity of the vulcanization activator is. In the patent document, expensive squalene needs to be added as a natural rubber simulator to be mixed with an accelerator and a vulcanization activator, and a DSC curve is tested to obtain the maximum exothermic temperature so as to judge the activity of the vulcanization activator. It is only aimed at screening vulcanization active agent in organic thiosulfate vulcanizing agent, and is not applicable to other vulcanizing agents. Furthermore, it is known from the description of paragraph 0048 of this patent document that, in order to screen for the activity of different vulcanization activators, the activators used need to contain the same amount of metal, i.e. the activities can be compared only for a batch of vulcanization activators which all contain the same metal and have the same metal content, for example zinc laurate, zinc acetate anhydrous, zinc benzoate and zinc oxide.

At present, the technical problems of screening strategies for sulfiding active agents remain to be solved.

Disclosure of Invention

The invention aims to overcome the defects that the screening of a vulcanizing activator in the prior art requires mixing, vulcanizing and other processes, the screening process is complex and high in cost, squalene is added as a natural rubber analogue to be mixed with an accelerator and the vulcanizing activator in the screening method adopting a differential scanning calorimetry (Differential Scanning Calorimetry, DSC), and only the vulcanizing activator containing the same amount of metal is screened, so that the screening range is small and the screening method is not suitable for other vulcanizing agents. The testing method disclosed by the invention does not need the steps of mixing, vulcanizing and the like, is suitable for screening the vulcanizing activator of the sulfenamide accelerator, has a wide screening range for the vulcanizing activator, and can realize the testing of the activities of different types of vulcanizing activators by using a differential scanning calorimeter.

The invention mainly solves the technical problems through the following technical scheme.

The invention provides a test method for detecting activity of a vulcanization activator, which comprises the following steps: and (3) performing differential scanning calorimetry test on the mixture of the to-be-detected vulcanization active agent and the sulfenamide accelerator to obtain the maximum exothermic peak temperature of the mixture.

In the present invention, those skilled in the art know that the temperature of the maximum exothermic peak is the temperature indicated in the abscissa corresponding to the top point of the maximum exothermic peak in the DSC curve of the mixture obtained by the differential scanning calorimetry test.

According to the testing method, the skilled person can know that when more than two types of to-be-detected vulcanizing active agents exist, the activities of the to-be-detected vulcanizing active agents are ordered according to the temperature of the maximum exothermic peak of the mixture, and screening of different to-be-detected vulcanizing active agents can be achieved. The smaller the temperature of the maximum exothermic peak of the mixture, the greater the activity of the sulfiding active agent to be detected.

In the present invention, the inventors have also found that, in order to further verify whether the to-be-detected vulcanization activator is capable of promoting the vulcanization activity of the sulfenamide accelerator, it is generally also necessary to perform a differential scanning calorimetry test on the sulfenamide accelerator to obtain the temperature of the maximum exothermic peak of the sulfenamide accelerator. If the temperature of the maximum exothermic peak of the mixture is measured to be lower than the temperature of the maximum exothermic peak of the sulfenamide accelerator, it is indicated that the vulcanization activator to be detected in the mixture can promote the decomposition of the sulfenamide accelerator, that is, can enhance the vulcanization activity of the sulfenamide accelerator; if the temperature of the maximum exothermic peak of the mixture is measured to be higher than the temperature of the maximum exothermic peak of the sulfenamide accelerator, it is indicated that the to-be-detected vulcanization active agent in the mixture delays the decomposition of the sulfenamide accelerator.

The inventors have found that the bond breaking of the sulfenamide accelerator is used as a sign of the start of vulcanization from the viewpoint of vulcanization mechanism, and the accuracy is high. By conducting DSC testing of the sulfenamide-based accelerator, it was found that the temperature of the maximum exothermic peak in the DSC curve is an indicator of N-S bond cleavage in the sulfenamide-based accelerator. Further, it is verified by experiments that the lower the temperature of the maximum exothermic peak in the DSC curve of the mixture of the vulcanization active agent to be detected and the sulfenamide accelerator is, the higher the activity of the vulcanization active agent is. The invention creatively combines bond breaking and DSC exothermic curve of the sulfenamide accelerator, is applied to the activity test of the vulcanization active agent, simplifies the test method of the activity of the vulcanization active agent by using DSC test in the prior art, and simultaneously expands the screening range of the vulcanization active agent.

In the present invention, the method for testing of the present invention is only to use the mixture of the to-be-tested vulcanization activator and the sulfenamide accelerator, and the sulfenamide accelerator is broken during the DSC test, and the type of the to-be-tested vulcanization activator is not particularly limited, and the conventional vulcanization activator in the art is adopted, and generally comprises metal oxide, stearate, laurate, carbon black or g-C ₃ N ₄ 。

The metal oxide is, for example, zinc oxide, copper oxide or calcium oxide.

The stearate is, for example, zinc stearate or calcium stearate.

The laurate is, for example, zinc laurate.

The carbon black is, for example, of the type N-330.

Said g-C ₃ N ₄ For example, urea is used as a raw material and calcined.

According to the test method, the N-S bond contained in the sulfenamide accelerator and the benzothiazole group connected with the N-S bond are required to be acted mutually, so that the N-S bond of the sulfenamide accelerator is broken in the DSC test process, and the method is further realized. Thus, the sulfenamide accelerator may be any sulfenamide accelerator generally used in the art, and generally refers to benzothiazole sulfenamides such as N-cyclohexyl-2-benzothiazole sulfenamide (abbreviated as CBS or CZ), N-tert-butyl-2-benzothiazole sulfenamide (abbreviated as NS), N-oxydiethylene-2-benzothiazole sulfenamide or N, N-dicyclohexyl-2-benzothiazole sulfenamide (abbreviated as DZ).

In the present invention, the person skilled in the art knows that, in order to avoid errors, a comparability of the activity between the same batch of the active agent to be tested is achieved, the parameters of the DSC test being kept identical in each batch of the test method. Such as the total mass of the mixture, the temperature of the DSC test, or the rate of rise of the DSC test, etc.

In the invention, the mass ratio of the to-be-detected vulcanization active agent to the sulfenamide accelerator in the mixture can be according to the conventional vulcanization ratio in the field, and is generally 1-5:1, for example, 2:1, 3:1 or 4:1.

In the present invention, the mixture may be obtained according to a preparation method conventional in the art, for example, by mixing and grinding the vulcanization activator to be detected and the sulfenamide accelerator.

In the present invention, the total mass of the mixture may be as required for DSC measurement, which is conventional in the art, and is generally 5 to 10mg, for example, 7mg, 8mg or 9mg.

In the present invention, the differential scanning calorimetry test conditions can be used as conventional test conditions in the art for testing exothermic curves of substances.

Wherein the differential scanning calorimetry test may have a ramp rate of from 5 to 20 ℃/min, for example 10 ℃/min.

The differential scanning calorimetry test generally needs to be carried out by introducing carrier gas, and the carrier gas can be one or more of nitrogen, helium and argon. Wherein the gas flow rate of the carrier gas purge is preferably 10-30 mL/min.

Wherein the onset temperature of the differential scanning calorimetry test is typically Room Temperature (RT), e.g. 10-30 ℃, specifically e.g. 25 ℃.

Wherein the termination temperature of the differential scanning calorimetry test is reasonably selected according to the temperature of the maximum exothermic peak of DSC test of the sulfenamide accelerator, and is generally 200-800 ℃, such as 300 ℃.

On the basis of conforming to the common knowledge in the field, the above preferred conditions can be arbitrarily combined to obtain the preferred examples of the invention.

The reagents and materials used in the present invention are commercially available.

The invention has the positive progress effects that:

(1) The testing method of the vulcanizing activator eliminates the traditional and complicated process of preparing the rubber compound, and simultaneously greatly reduces the energy consumption required in the process; the variety and quality of samples used in DSC test are greatly reduced compared with the traditional method, and the cost is remarkably reduced.

(2) The method for testing the vulcanization activator takes the broken bond of the N-S bond in the sulfenamide accelerator as a sign of vulcanization start from the perspective of vulcanization mechanism, and has quite accuracy when being applied to judging the activities of different vulcanization activators to be detected.

(3) The test method is suitable for detecting the vulcanization active agent aiming at the sulfenamide accelerator, can be suitable for detecting the activity of different types of vulcanization active agents, and has no limit on application range.

Drawings

FIG. 1 is a DSC plot of a mixture of CBS and carbon black from example 1.

FIG. 2 is a DSC plot of a mixture of CBS and zinc oxide of example 2.

FIG. 3 shows CBS and g-C in example 3 ₃ N ₄ DSC test plot of the mixture of (c).

Fig. 4 is a DSC test plot of a mixture of CBS and zinc stearate in example 4.

Fig. 5 is a DSC test plot of CBS in the blank.

FIG. 6 is a graph showing the vulcanization of a compound made from CBS and a curing activator to be tested.

Detailed Description

The invention is further illustrated by means of the following examples, which are not intended to limit the scope of the invention. The experimental methods, in which specific conditions are not noted in the following examples, were selected according to conventional methods and conditions, or according to the commercial specifications.

The sources and instrument models of the raw materials used in examples 1 to 5 below were as follows:

carbon black: carbon black model number (N-330) of Shanghai Kabo chemical Co., ltd; zinc oxide: national chemical agents, inc; zinc stearate: shanghai Miclin Biochemical technologies Co., ltd; n-cyclohexyl-2-benzothiazole sulfenamide (CBS): shanghai addition chemical Co., ltd. Model of DSC instrument: modulated DSC2910, 1090B.

g-C ₃ N ₄ : prepared by a preparation method conventional in the art, weighing urea with a certain mass, placing the urea into a crucible, calcining the urea for 2 hours at 550 ℃ by adopting a muffle furnace, and then cooling the urea along with the furnace to obtain g-C ₃ N ₄ 。

Example 1

Mixing and grinding carbon black and accelerator CBS in a mass ratio of 5:1 to obtain mixed powder; 8mg of the mixed powder was taken and DSC was performed.

The experimental parameters of DSC were set as follows, rate of temperature rise: 10 ℃/min, temperature range: RT-300 ℃ (initial temperature is 25 ℃, end temperature is 300 ℃), nitrogen atmosphere, and the flow rate of nitrogen purging is 10mL/min; a DSC profile was obtained as shown in figure 1. From the figure, it can be seen that when CBS is mixed with carbon black, the carbon black has a promoting effect on the decomposition of CBS, and the decomposition temperature is 204 ℃, i.e., the temperature of the maximum exothermic peak.

Example 2

Mixing and grinding zinc oxide and accelerator CBS in a mass ratio of 4:1 to obtain mixed powder; 8mg of the mixed powder was taken and DSC was performed.

The DSC experimental parameters were set as follows, the heating rate is 10 ℃/min, and the temperature range is: RT-300 ℃ and nitrogen atmosphere; a DSC profile was obtained, as shown in fig. 2, from which it was found that zinc oxide had a promoting effect on the decomposition of CBS when CBS was mixed with zinc oxide, and the decomposition temperature was 200 ℃, i.e., the temperature of the maximum exothermic peak.

Example 3

Will g-C ₃ N ₄ Mixing and grinding with accelerator CBS at a mass ratio of 2:1; 8mg of the mixed powder was taken and DSC was performed.

The experimental parameters of DSC were set as follows: the temperature rising rate is 10 ℃/min, the temperature range is RT-300 ℃, and the nitrogen atmosphere is adopted; DSC graphs are shown in FIG. 3, from which CBS and g-C can be obtained ₃ N ₄ After mixing, g-C ₃ N ₄ The CBS has inhibition effect on the decomposition, and the decomposition temperature is 209 ℃, namely the temperature of the maximum exothermic peak.

Example 4

Mixing and grinding zinc stearate and accelerator CBS in a mass ratio of 3:1; 8mg of the mixed powder was taken and DSC was performed.

The experimental parameters of DSC were set as follows, rate of temperature rise: 10 ℃/min, temperature range: RT-300 ℃ and nitrogen atmosphere; the DSC graph is shown in FIG. 4, from which it is possible to obtain a temperature at which zinc stearate has an inhibitory effect on decomposition of CBS, i.e., a maximum exothermic peak, when CBS is mixed with zinc stearate, the decomposition temperature being 211 ℃.

Blank control group: DSC was performed with 8mg of accelerator CBS. The experimental parameters of DSC were set as follows: the temperature rising rate is 10 ℃/min, the temperature range is RT-300 ℃, and the nitrogen atmosphere is adopted; the DSC graph is shown in FIG. 5, from which the melting point of the accelerator CBS is 103℃and the decomposition temperature is 207℃and is the temperature of the maximum exothermic peak. The decomposition temperatures of the mixed powders in the respective examples were compared with this standard temperature, and preliminary screening of the rubber vulcanization activator was performed. Based on the difference in the decomposition temperature of CBS in the above four examples, the order of vulcanization activity was preliminarily determined as: znO > carbon black > g-C ₃ N ₄ Zinc stearate.

And (3) verifying the validity of a screening method: the four vulcanization activators used in examples 1 to 4 were added to the rubber mixing process to ensure that the other formulations were the same and the formulation of the mixture was specifically: 100phr of raw styrene-butadiene rubber, 1.75phr of sulfur, 1phr of accelerator CBS, 1phr of stearic acid and 5phr of the vulcanization activator to be verified in examples 1 to 4, wherein phr represents parts per hundred parts of rubber, and a rubber compound is obtained.

The four mixes were tested for cure curves using a Uken technologies Co., ltd/UR-2010 SD intelligent rotor-less vulcanizer, as shown in FIG. 6. The scorch time and cure rate of the four mixes were calculated from the cure curves and compared to confirm the effectiveness of the screening method and test results are shown in table 1 below.

According to the vulcanization curve, the arrangement sequence of scorch time (Tc 10) of the rubber compound for obtaining the four vulcanization active agents is as follows: zinc stearate > g-C ₃ N ₄ Carbon black > ZnO. The four mixes were arranged in the following order of Cure Rate (CRI): znO > carbon black > g-C ₃ N ₄ Zinc stearate. The results completely conform to the activity sequence of the vulcanization activator determined according to the CBS decomposition temperature, and prove the effectiveness of the screening method of the rubber vulcanization activator.

TABLE 1

	Tc10	Tc90	CRI	MH	ML
						Carbon black	612S	1263S	0.154	6.34	0.69
ZnO	551S	1185S	0.158	6.52	0.65
						g-C ₃ N ₄	626S	1319S	0.144	5.76	0.64
Zinc stearate	687S	1382S	0.143	3.99	0.65

Claims

1. A test method for detecting the activity of a sulfiding activator, comprising the steps of: performing differential scanning calorimetry test on the mixture of the to-be-detected vulcanization active agent and the sulfenamide accelerator to obtain the maximum exothermic peak temperature of the mixture;

the to-be-detected vulcanization activator comprises metal oxide, stearate, laurate, carbon black or g-C ₃ N ₄ ；

The temperature of the maximum exothermic peak in the curve obtained by the differential scanning calorimetry is a sign of N-S bond cleavage in the sulfenamide accelerator, and the bond cleavage of the sulfenamide accelerator is used as a sign of vulcanization start.

2. The method for detecting the activity of a vulcanization activator of claim 1, wherein the sulfenamide accelerator is a benzothiazole sulfenamide compound.

3. The method of claim 2, wherein said benzothiazole sulfenamide compound comprises N-cyclohexyl-2-benzothiazole sulfenamideN-tert-butyl-2-benzothiazole sulfenamide>N-oxydiethylene-2-benzothiazole sulfenamide +.>Or N, N-dicyclohexyl-2-benzothiazole sulfenamide +.>。

4. The method for detecting the activity of a sulfidizing activator of claim 1, wherein the metal oxide is zinc oxide, copper oxide or calcium oxide;

and/or the stearate is zinc stearate or calcium stearate;

and/or, the laurate is zinc laurate;

and/or the model of the carbon black is N-330;

and/or, said g-C ₃ N ₄ Urea is used as raw material and calcined to obtain the final product.

5. The method for detecting the activity of a vulcanization activator according to claim 1, wherein the mass ratio of the vulcanization activator to be detected to the sulfenamide accelerator in the mixture is 1-5:1.

6. The method of claim 5, wherein the mass ratio of the sulfiding active agent to the sulfenamide accelerator is 2:1, 3:1 or 4:1.

7. The method for detecting the activity of a vulcanization activator according to claim 1, wherein the mixture is prepared by mixing and grinding the vulcanization activator to be detected and the sulfenamide accelerator.

8. The method for detecting the activity of a vulcanization activator according to claim 1, wherein the total mass of the mixture is 5 to 10mg when the mixture is tested by differential scanning calorimetry.

9. The method of claim 8, wherein the total mass of the mixture is 7mg, 8mg or 9mg when tested by differential scanning calorimetry.

10. The test method for detecting the activity of a vulcanization activator according to claim 1, wherein the temperature rise rate of the differential scanning calorimetry test is 5-20 ℃/min;

and a carrier gas is also required to be introduced during the differential scanning calorimetry test.

11. The method of claim 10, wherein the differential scanning calorimetry test has a ramp rate of 10 ℃/min.

12. The test method for detecting the activity of a sulfiding activator of claim 10, wherein the carrier gas is one or more of nitrogen, helium and argon;

the air flow speed of the carrier gas purging is 10-30 mL/min.

13. The method for detecting the activity of a vulcanization activator according to any one of claims 1 to 12, wherein the initial temperature of the differential scanning calorimetry test is room temperature;

the termination temperature of the differential scanning calorimetry test is 200-800 ℃.

14. The method for detecting the activity of a vulcanization activator according to claim 13, wherein the initial temperature of the differential scanning calorimetry test is 10 to 30 ℃;

the termination temperature of the differential scanning calorimetry test was 300 ℃.

15. The method of claim 14, wherein the onset temperature of the differential scanning calorimetry test is 25 ℃.