Development of Acrylonitrile Grafted SIS Adhesive

Abstract: Graft copolymerization of acrylonitrile as monomer and SIS in mixed solvent was made to graft modified SIS adhesives. The influence of polymerization conditions and formulas on adhesive properties was discussed. The suitable process conditions are: reaction temperature 75~80°C, reaction time 3.5~4.0h, initiator dosage 0.8%~1.0%, state dosage 25% of SIS.

Key words: SIS; adhesive; graft copolymerization; acrylonitrile

Foreword

SIS is a polystyrene-polyisoprene-polystyrene triblock copolymer. It is a very important thermoplastic elastomer. It is mainly used as a raw material for hot-melt adhesives and pressure-sensitive adhesives. It can also be used for coatings and plastics. Modification, asphalt modification and so on. SIS has the properties of vulcanized rubber at room temperature and exhibits plasticity at high temperatures. It has good solubility, high adhesion, and high tensile strength. In addition, it has the characteristics of small melt viscosity, small solution viscosity, high elasticity, small modulus, easy processing, reusable material, etc., so its application range and demand are increasing. However, the SIS has a small polarity, poor oil resistance and solvent resistance, and its application range is greatly limited. In order to improve its performance, polar groups can be introduced into its main chain. Since it is impossible to introduce polar groups in the anionic polymerization process it produces, it is feasible to introduce polar groups into its chemical modification. The way. Due to the presence of unsaturated bonds in the SIS, suitable monomers can be selected to graft modify the SIS. People have done a lot of research on the graft modification of SBS, and there is no report on the graft modification of SIS. This article intends to discuss the graft modification process conditions and ratio of SIS in order to obtain excellent performance. SIS adhesives.

1 Experimental section

1.1 Raw materials:

SIS: industrial products, produced by Yueyang Petrochemical Plant; benzoyl peroxide (BPO): analytically pure, Tianjin Dongfang Chemical Factory; toluene, ethyl acetate, and acrylonitrile are all chemically pure reagents.

1.2 Major equipment

JJ-1 Timing Electric Stirrer: ZhengTan ZhengJi Co., Ltd., Jiangsu Province; Electric Constant Temperature Water Bath: Beijing Tektronix Co., Ltd.; Automatic Electro-Optical Analysis Balance: XiangYi Balance Instrument Factory; WSM-20K Digital Tester: Changchun Intelligent Experimental Machine Research Institute; electric constant temperature drying oven: Shandong Weifang Pharmaceutical Co., Ltd. medical machinery factory; STA409PC thermal analyzer, Germany Netzsch company production; glass equipment; Utz viscometer.

1.3 Graft polymerization

In a four-necked flask equipped with an electric stirrer, a reflux condenser, a thermometer, and a dropping funnel, a mixed solvent and a quantitative amount of SIS are added, stirred at a temperature to completely dissolve the mixture, and after heating to a suitable temperature, a small amount of a mixture containing the initiator is added. Monomer, and then the side of the reaction while adding a mixed monomer dissolved initiator, the reaction temperature 3.5 ~ 4.0h after discharge.

1.4 Performance Analysis

The prepared glue was uniformly coated on 25 mm wide kraft paper, and most of the solvent was baked in a constant temperature drying oven. Initial tack test: Using a self-made tack tester, place a small steel ball at a 10 cm incline on a 30° incline and measure the distance it rolls on a horizontal tape.
180° peel strength: refer to GB7126-86 standard, test with WSM-20K digital tester;
Shear strength: Refer to GB7124-86 standard, test with WSM-20K digital tester;
Sticky: According to GB485-84 test;
Viscosity: According to GB2794-91 standard test;
Solid content: According to GB2793-91 standard test.

2 Results and Discussion

2.1 Effect of polymerization temperature on graft copolymerization

The polymerization temperature has a great influence on the polymerization reaction time and the performance of the glue. When the temperature is lower than 75°C, the energy of the reaction molecules is small and the reaction takes a long time. The viscosity of the prepared liquid is low and the adhesive force is also small. In addition, the glue liquid has a large acrylonitrile monomer smell. It indicates that the reaction is not complete and the monomer grafting rate is low; with the increase of polymerization temperature, the adhesive force of the glue liquid gradually increases. When the temperature is higher than 80° C., the molecular energy is too large and the reaction is rapid. Gels are easily present in the gel, which reduces the adhesive strength of the glue. Considering various factors comprehensively, the polymerization temperature is controlled at about 75-80°C, which is appropriate. The effect of polymerization temperature on 180° peel strength of glue liquid is shown in Figure 1 .

2.2 Effect of Reaction Time on Performance of Polymerization Products

When the composition of the system is constant and the graft copolymerization reaction is carried out at a suitable temperature, the length of the reaction time also has a great influence on the performance of the glue solution. See Figure 2.

As can be seen from Fig. 2, with the progress of the reaction, the adhesive force of the glue liquid continuously increases, but when the reaction proceeds for 3.5 to 4.0 hours, the adhesive force of the glue liquid instead decreases. The reason for this is that with the progress of the reaction, the grafting rate of the SIS and the monomer is continuously improved, and the adhesive property of the glue liquid is enhanced. However, if the reaction time is too long, the side reaction increases, resulting in a poor grafting effect, so the polymerization reaction time 3.5 ~ 4.0h is appropriate.
2.3 Effect of BPO on the performance of glue

When the composition of the system, the reaction temperature and the reaction time are fixed, the amount of initiator (BPO) also has a great influence on the adhesive properties of the adhesive. See Figure 3.

As can be seen from Figure 3, with the increase in the amount of BPO, the adhesive strength of the glue increases, but when the amount of BPO exceeds 1.0% of the total amount of SIS, the adhesive force of the product decreases. The reason is that as the amount of BPO increases, the monomer conversion rate increases and the grafting efficiency increases. However, excessive BPO consumption leads to an increase in induced decomposition, resulting in an increase in the number of low-molecular-weight polyacrylonitriles and possible oxidation of some of them. The monomer (the color of the product is deepened to illustrate this), but the graft rate is reduced, and thus the viscous properties are affected. Therefore, the amount of BPO should be controlled between 0.9% and 1.0%.

2.4 Effect of Acrylonitrile Consumption on Performance of Adhesive

Under the action of initiator BPO, acrylonitrile is graft copolymerized with the double bond in SIS to increase its polarity and toughness. The mass fraction of acrylonitrile has a great influence on the performance of the glue. The results are shown in Table 1. .

As can be seen from Table 1, with the increase of the amount of acrylonitrile, the initial viscosity, stickiness, 180° peel strength and shear strength of the glue are all increased. When the mass fraction reaches 25%, the adhesive property of the glue is the best. With the continuous increase of the amount of acrylonitrile, the performance indicators of the glue solution have become worse, indicating that the grafting effect of acrylonitrile at the mass fraction of 25% is the best, and when the acrylonitrile is greater than 25%, the grafting effect will be worse. It can be confirmed by the change of the solid content and viscosity of glue.

3. Heat resistance analysis

Graft polymerized colloids with an acrylonitrile mass fraction of 25% were subjected to differential scanning calorimetry in an oxygen and inert gas atmosphere, respectively, to investigate their thermal stability. The results show that the glue solution is stable at temperatures below 350°C in an inert atmosphere and is stable at temperatures below 320°C in oxygen atmosphere. Below 300°C, the mass fraction decreases slightly, probably due to solvent evaporation and decomposition of small molecules.

4 Conclusion
(1) Acrylonitrile can effectively graft SIS under the induction of BPO, increase its polarity and toughness, and improve its bonding strength with polar surface materials.

(2) Acrylonitrile quality under the conditions of toluene and ethyl acetate as solvent, reaction temperature 76-80°C, reaction time 3.5-4.0 h, initiator dosage 0.9%-1.0% When the score is 25%, the grafting effect is better.

(3) The modified SIS adhesive has higher thermal stability and adhesive strength. (Yang Xingkun Zhang Xiulan Wang Wenbin