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10 examples of formulations of polyvinyl acetate emulsion adhesives

 Last Update: 2021-07-28
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(1) Monomer

The monomer is vinyl acetate, also known as vinyl acetate (VAC), the structural formula is CH3C0OCH=CH2

Emulsion polymerization is the same as free radical addition polymerization.

It requires very high monomer purity.

(2) Emulsifier

The reaction generally uses two non-ionic emulsifiers, namely nonylphenol polyoxyethylene ether (OP-10) and polyvinyl alcohol

(3) Initiator

Persulfates, such as ammonium persulfate and potassium persulfate can be used as initiators

(4) Other additives

Plasticizer dibutyl phthalate

Preservatives sodium nitrite, sodium benzoate

Defoamer octanol

Dispersant methanol

Antifreeze Glycol

(5) Water

Use deionized water, because tap water contains metal ions, which can inhibit the polymerization reaction.

If tap water is used as a raw material, ethylenediaminetetraacetic acid must be added as a integrator
.

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The initiation reaction of emulsion polymerization takes place in the micelles, and the polymerization reaction is mainly carried out in the micelles after the initiation and the polymer particles formed therefrom.
The monomer droplets mainly play the role of monomer storage
.
Because the number of micelles is very large, almost only one free radical can be contained in a micelle, so the chain termination speed is significantly reduced, resulting in a faster emulsion polymerization rate and a high molecular weight of the obtained polymer
.
Vinyl acetate emulsion polymerization is a type of free radical polymerization.
It follows the general law of free radical polymerization and needs to go through three main stages: chain initiation, chain growth, and chain termination
.
The mechanism of the polymerization reaction is described below
.

(1) Chain initiation of polymerization reaction

The monomer, water, emulsifier, initiator and other materials are added to the reactor and stirred to form an emulsion

.
Vinyl acetate emulsion polymerization usually uses persulfate as the initiator, such as potassium persulfate or ammonium persulfate.

(2) Chain growth of polymerization reaction

The monomer free radicals are combined with the monomers to initiate polymerization to form chain free radicals, and the consumed monomers are continuously replenished by the monomer droplets through the water phase diffused into the micelles, and so on, the monomer molecules are initiated to start the polymerization reaction.

The polymer chain continues to grow, thereby obtaining high molecular weight polymers
.

As the initiator continues to decompose, the initiation reactions in the micelles continue to occur, and the number of active particles increases rapidly.

At this time, the chain termination rate is still relatively small, so the overall polymerization reaction rate is on the rise

The polymerization reaction proceeds at a constant rate, and at the same time, the surface tension of the water phase increases significantly
.
When the monomer conversion rate reaches 60%-70%, the monomer droplets gradually become smaller and all disappear
.

(3) Chain termination of polymerization reaction

At this time, the monomer droplets no longer exist, and the remaining monomer is present in the polymer particles and is adsorbed or swollen by the polymer
.

3 Synthetic process of polyvinyl acetate emulsion

(1) Reaction temperature

The reaction temperature is 75-85°C, and the reaction temperature affects the polymerization rate and the average molecular weight of the emulsion
.
Increasing the reaction temperature speeds up the generation of free radicals.
The monomer activity increases, the chain growth rate constant increases, and thus the polymerization reaction rate increases
.
As the reaction temperature rises.
The decomposition rate constant of the initiator increases.
When the concentration of the initiator is constant, the generation rate of free radicals increases, which causes the chain termination rate in the latex to increase, and the average relative molecular weight of the emulsion decreases
.

Increasing the reaction temperature will also increase the number of latex particles.
The average diameter decreases; the reaction temperature increases, causing collisions between the latex particles, increasing the coalescence rate, and the thinning of the hydration layer on the surface of the latex particles, which will cause the stability of the emulsion to decrease
.
If the reaction temperature is equal to or higher than the cloud point of the emulsifier, the emulsifier loses its stabilizing effect, causing demulsification
.

(2) Response time

The reaction time is 8-9h
.
The reaction time is also an important factor affecting the quality of polyvinyl acetate emulsion
.
The reaction time is mainly reflected in the length of the vinyl acetate dripping time.
The longer the vinyl acetate dripping time, the smaller the emulsion particles, the more uniform the particle size, the greater the strength of the emulsion, the better the stability, the better the transparency of the film, and the better the water resistance.
Improve
.

(3) Feeding method

Even with the same emulsion polymerization formula.
Due to the different methods of operation, resulting in an emulsion particle size distribution, and other aspects of molecular weight sizes not differ
.
There are three feeding methods as follows
.

①One-time addition method

All the components are added into the reactor at the same time for polymerization
.
Since vinyl monomers have a greater thermal effect during polymerization, and the emulsion polymerization reaction speed is faster, for industrial-scale devices, this feeding method brings greater difficulties to temperature control.
Therefore, this method is only used when the water and oil are relatively large
.
Sometimes in order to control the rate of heat release to maintain a certain polymerization temperature, the initiator is added in batches
.
The one-time addition method is less used in actual production
.

②Monomer dropping method

That is, the monomer is slowly and continuously added to the aqueous solution of the emulsifier, and the aqueous solution of the initiator is often dropped at the same time, and the temperature of the polymerization reaction is controlled at the rate of dropping
.
Since this method is convenient to operate and easy to control the polymerization reaction, it is widely used
.

③Emulsion dripping method

That is, the materials are mixed in advance to form an emulsion, and then gradually added dropwise to the reaction system for polymerization
.
The polymerization temperature is relatively easy to control, but this method requires pre-emulsification.
Generally, under the conditions of the emulsion polymerization formula, the monomer emulsion has poor stability and is easy to layer.
Therefore, pre-emulsification equipment must be equipped, which increases equipment investment And power consumption, so it is rarely used
.

(4) Synthetic operation method of polyvinyl acetate emulsion

The preparation of polyvinyl acetate emulsion can be synthesized by chemical method and short irradiation method.
The particle size of the emulsion prepared by irradiation method is not uniform and requires high equipment, so this method is generally not used.
Only the chemical method is introduced here
.
The chemical method has two modes: batch operation and continuous operation.
The specific preparation process is introduced below
.

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Continuous emulsion polymerization

a.
Put an amount of deionized water and polyvinyl alcohol (PVA) into the dissolving kettle, pass steam into the jacket of the dissolving kettle, raise the temperature to 80~85℃, stir and dissolve for 4~6h, so that the PVA is completely dissolved.
Into 10% (mass) PVA solution
.

b.
After filtering the prepared 10% (mass) PVA solution, put it into the polymerization kettle together with OP-10
.
Start the stirring to fully mix, and then put the vinyl acetate (about 1/7 of the total amount) and 10% (mass) potassium persulfate solution (about 2/5 of the total amount) in the metering tank into the polymerization kettle.
, Stir and emulsify for 30min
.

c.
Pour steam into the jacket of the polymerization kettle, raise the temperature of the materials in the kettle to 60-65°C, and stop heating
.
At this time, the polymerization reaction starts.
Because it is an exothermic reaction, the temperature in the kettle automatically rises to 75~85°C.
At this time, reflux will appear in the reflux condenser.
When the reflux is reduced, start to drip into the polymerizer through the metering tank.
Add vinyl acetate, and drip potassium persulfate solution through the metering tank [add 4% to 5% (mass) of potassium persulfate per hour]
.
Control the dripping rate to keep the polymerization temperature at 78~80℃, and the dripping is completed in about 8 hours
.

d.
After the monomer has been added, add all the remaining potassium persulfate solution to terminate the reaction chain
.
After all the materials have been added, the temperature will automatically rise to 90~95℃ and keep for 30min
.

e.
Pour cold water into the jacket of the polymerizer to cool the product to 50°C, add the specified amount of sodium bicarbonate solution and DBP and other additives through the metering tank, stir thoroughly to make it evenly mixed, and discharge after filtering
.

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Batch emulsion polymerization

a.
Add PVA and water to the dissolving kettle and raise the temperature to 80~85℃.
Stir and dissolve for 2h, and prepare a 10% (mass) PvA solution
.

b.
After filtering the PVA aqueous solution, put it into the polymerization kettle, add OP-10 and the primer monomer vinyl acetate, close the feeding hole, and open the cooling water
.
The temperature is raised to about 65°C within 30mm.
When liquid drops appear in the sight glass, the heating is stopped and the temperature can rise to 75-85°C by itself
.

c.
When the reflux is normal, start to add vinyl acetate monomer dropwise
.
Add 4% to 5% ammonium persulfate every hour, and control the uniform polymerization by adjusting the addition rate
.
The reaction temperature is controlled at 75-80°C, which can be adjusted by the amount of monomer added
.

d.
After the monomer is added, add the remaining ammonium persulfate, the temperature of the liquid material rises to 90~95°C by itself, and the temperature is kept for 30 minutes
.
Cool to below 50°C and add 10% sodium bicarbonate solution
.

4 Formulation example of polyvinyl acetate emulsion adhesive

[Recipe] 1

Component	Mass parts
Vinyl acetate	100
Polyvinyl alcohol 1788	5. 4
OP-10	1. 1
Dibutyl phthalate	10. 9
Potassium persulfate	0. 2
Sodium bicarbonate	0. 3
Deionized water	100

Uses: Synthesize polyvinyl acetate emulsion
.
It can be used for wood, paper, packaging and construction
.

[Recipe] 2

Component	Mass parts
Vinyl acetate	355
Polyvinyl alcohol	31. 5
OP-10	4
Ammonium persulfate	0. 72
Sodium bicarbonate	1. 1
Dibutyl phthalate	4
water	318

Uses: Synthesize polyvinyl acetate emulsion
.
It can be used for wood, paper, packaging and construction
.

[Recipe] 3

Component	Mass parts
Polyvinyl acetate emulsion	40~100
cement	100
Fine sand	100
Calcium chloride	1
water	Right amount

Uses: Used for bonding concrete and repairing docks
.

[Recipe] 4

Component	Mass parts
Vinyl acetate	50
Polyvinyl alcohol 1788 and 1799	8
OP-10	0. 6
Ammonium persulfate	0. 1
Sodium bicarbonate	Right amount
Dibutyl phthalate	12. 5
Octanol	0. 3
Ethylene glycol	1
Aluminum Nitrate	0. 4
water	65

Uses: Synthesize polyvinyl acetate emulsion
.
It can be used for wood, paper, packaging and construction
.

[Recipe] 5

Component	Mass parts
Vinyl acetate	100
Sodium Oleate	0. 1~0. 5
hydrogen peroxide	0. 5~1. 5
water	100~120

Uses: for wood, paper, packaging and the like
.

[Recipe] 6

Component	Mass parts
Vinyl acetate (initial charge)	150
Vinyl acetate (total)	1047
5% (mass) polyvinyl alcohol solution	1047
Hydrogen peroxide [40% (mass)]	3. 3
Methanol	1. 04

Uses: for wood, paper, packaging and the like
.

[Recipe] 7

Component	Mass parts
Polyvinyl acetate emulsion	55
Polyvinyl alcohol 1799	3
Trichloroethylene	9
Dibutyl phthalate	5. 5
preservative	0. 3
Defoamer	0. 2

Uses: can be used for wood, paper, packaging and construction, etc.

[Recipe] 8

Component	Mass parts
Polyvinyl acetate emulsion	31
Polyvinyl alcohol 1799	5
Clay	10
Dibutyl phthalate	3. 5
water	50
preservative	0. 5
Defoamer	0. 2

Uses: can be used for wood, paper, packaging and construction, etc.

[Recipe] 9

Component	Mass parts
Polyvinyl acetate emulsion	97
Dibutyl phthalate	3. 0~7. 0

Uses: can be used for wood, paper, packaging and construction, etc.

[Recipe] 10

Component	Mass parts
Vinyl acetate	44
Polyvinyl alcohol 1788	4
Ethanol	0. 2
Ammonium persulfate	Right amount
Dibutyl phthalate	6
water	55

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