Development of freeze-thaw resistant polyvinyl acetate emulsion adhesive

1.3 Performance Testing and Analysis Methods

1.3.1 Emulsion viscosity

Use NDJ-1 rotary viscometer, according to GB2794.

1.3.2 pH

Take 1-2g of the emulsion in a container, dilute with water, and test with a pHS-2 acidity meter.
1.3.3 Solids content (gravimetric method)

Weigh 1–2 g of the emulsion in a container and level it. Place it in an oven at 115±5°C for 2-4 h until constant weight. Place in a desiccator and cool to room temperature.

Calculation: G%=W/W0*l00%

Where: C-solids content/%; W-weight of sample after drying/g; W0-weight of sample before drying/

1.3.4 Dilution stability

The emulsion was diluted with distilled water to a non-volatile content of 3±0.5%. 100 ml of the diluted solution was added to a graduated cylinder and allowed to stand for 72 hours. The volume (ml) of the supernatant and the precipitate was determined by observation.

1.3.5 Freeze-thaw stability

Weigh 50-100g samples in plastic bottles, place them in a -20%±0.5°C freezer, freeze for 16h, and take them out in a 30°C oven to melt for 2h as a freeze-thaw cycle to observe the state of emulsion (agglomerate The phase separation is unqualified, but after being stirred, it can be restored to uniform emulsion and even emulsion as qualified. The emulsion viscosity is measured and the viscosity change rate before and after freezing and thawing of the emulsion is calculated. The following formula is used to calculate:

σ%=(η1-η0)/η0*100%

Where: η-viscosity change rate/%; η1-viscosity after freezing and thawing; η0-initial viscosity
1.3.6 Storage stability

Place the emulsion for more than half a year and observe the state of the emulsion (agglomerate into chunks, phase, and uneven, but after mixing, it can be restored to uniform emulsion and homogeneous emulsion).

1.3.7 Shear Strength

See HG/T2727-95.

1.3.8 Surface carboxyl group content and distribution

The distribution of surface carboxyl groups was diluted according to the method described in [3]. The emulsion was diluted to 1-2% of solid content. After sufficient amount of anion-cation exchange resin was exchanged and filtered, the pH was adjusted to approximately 11.0±0 with 0.5N NaOH. 2, titration with 0.1256 NH2SO4 under electromagnetic stirring, while monitoring the conductance and pH of the system, determine the volume of acid consumed, the titration end point is 2.5 ± 0.2, the typical conductivity titration curve shown in Figure 2, Figure 3 . Finally, the data is processed according to [3].

(to be continued)