Issue 49/2014 - Research status and trend of modification of waterborne polyurethanes

Research status and trend of modification of waterborne polyurethane

□ Shanghai Heshibi Chemical Co.
, Ltd.
Ji Yanjie

Waterborne polyurethane (WPU), or polyurethane emulsion, is usually a dispersion of ionic polyurethane in water, so it is very closely
related to ionic polyurethane.
In order to improve some deficiencies in the performance of the resin itself and improve the comprehensive performance of the resin to expand its scope of use, it is often necessary to modify
waterborne polyurethane.
There are many ways to modify waterborne polyurethanes, including blending modification, copolymerization modification, polyacrylate modification, epoxy resin modification, silicone modification, nano modification, etc
.

1.
Modification research

1.
Blended modified
waterborne polyurethane can be blended with emulsions with similar ionic and acid-alkaline properties to obtain the modification effect
conveniently.
Studies have shown that waterborne polyurethanes can be blended with emulsions of polyvinyl alcohol, polyvinyl acetate, epoxy resin, polysiloxane and other resins to obtain functional products
.

2.
Copolymerization modified polyurethane chemical properties are more active, under the action of catalyst, the -NH- group in carbamate can copolymerize with acrylate monomers to form
polyurethane.

Waterborne polyurethanes can also be copolymerized with epoxy resins, vinyl ester resins (VER), polysiloxanes and other resins
.
Epoxy resin has excellent strength, modulus and adhesion properties, and its modification of polyurethane systems can obtain good toughness
.
There have been reports of
VER modified polyurethane elastomers for high-impact materials abroad.

3.
Polyacrylate modified
polyacrylate (PA) resin has excellent light fastness, weather resistance, is not easy to yellowing when exposed to ultraviolet radiation, resists acid, alkali and salt corrosion, has high flexibility and low
price.
The use of polyacrylate modified waterborne polyurethane can combine the excellent properties of waterborne polyurethane with the good adhesion and weather resistance of polyacrylate resin, so as to prepare a high-solids, low-cost waterborne resin, which improves the comprehensive performance of waterborne polyurethane resin and reduces the cost of the product, which has broad application prospects
.

Chen Jinlian et al.
prepared acrylic modified waterborne polyurethane emulsion by equilibrium swelling method, and found that the content of methyl methacrylate (MMA) could be greatly improved, and the performance of modified waterborne polyurethane emulsion and coating film
could be significantly improved.
Wu Dongmei et al.
used butyl acrylate (BA) and MMA to prepare waterborne polyurethane/polyacrylate composite emulsion by copolymerizing with waterborne polyurethane emulsion, and the results showed that the prepared composite emulsion had good storage stability and film-forming performance
at room temperature.
Compared with waterborne polyurethane emulsion, the particle size of the composite emulsion is increased, the substrate wetting is better, and the water resistance of the adhesive film is significantly improved
.
Wang Zhiqiang et al.
synthesized MMA modified waterborne polyurethane emulsion, scanning electron microscopy showed that the surface of the modified waterborne polyurethane film was relatively flat, because the degree of microphase separation of polyurethane and acrylate was small, the compatibility was good, and the comprehensive performance of acrylate waterborne polyurethane obtained when m(PU):m(PA)=8:2 was better
.

4.
The structure of epoxy resin modified epoxy resin has hydroxyl ether bonds and epoxy end groups, strong polarity and not easy to hydrolyze, the modification of polyurethane with epoxy resin can greatly improve the adhesion of
the coating film to the substrate, improve the water resistance, heat resistance, solvent resistance and chemical resistance of the coating
.

5.
Silicone modified
silicone compounds have low surface energy, low temperature resistance, aging resistance, hydrophobicity, organic solvent resistance, radiation resistance and good air permeability, and can also give the coating outstanding flexibility and smooth silk feel
.
As a result, silicones can be used to improve the heat resistance and moisture rubbing resistance
of waterborne polyurethanes.
Polyurethane-organosilanes are often combined by chemical synthesis to bring out the benefits of
both polyurethanes and silicones.

Researchers have synthesized waterborne polyurethane prepolymers with isophorone diisocyanate, polytetrahydrofuranediol, dihydroxymethylpropionic acid and trimethylolpropane as raw materials, and used 3-aminopropyltriethoxysilane (KH550) for end-capping modification, and further hydrolyzed condensation and crosslinking after emulsification to obtain waterborne polyurethane
with high crosslinking.
The FTIR characterization results showed that -NH2 on KH550 underwent a heavy bond addition reaction
with the end-NCO of polyurethane.
After KH550 modification, the mechanical properties, heat resistance, water resistance and solvent resistance of the adhesive film are significantly improved; With the increase of KH550 content, the crystallinity of the film is small
.

6.
Nano-modified
nanoparticles have special surface effect, volume effect, quantum size effect and macroscopic quantum tunneling effect, and can produce strong physical and chemical effects with polymers, which are widely used in the strengthening and toughening modification of polymer materials, and have also been reported
in polyurethane modification.

Experts have prepared nano-HA/PU composites by prepolymerization method using H12MDI, polyethylene glycol, castor oil, 1,4-butanediol and bioactive nano-hydroxyapatite (n-HA) as raw materials, and studied their mechanical and thermal properties
.
It is found that with the increase of n-HA content, the tensile strength and elongation at break of the film increase, the energy storage modulus is significantly improved, the thermal stability is also improved, and when the dosage is 30%, the comprehensive mechanical properties of the composite material reach the best
.

Nano-modification of waterborne polyurethane can improve mechanical strength, thermal stability, corrosion resistance and aging resistance
.
The nano-modified waterborne polyurethane composite material can be widely used in textile, construction, automotive, aviation and other fields
.

Second, the application field

The application of waterborne polyurethane is mainly in the two major fields of coatings and adhesives, such as wood paint and wood floor paint, paper layer, architectural coating, leather finishing agent, of which the most used is architectural coating.

At present, waterborne polyurethane adhesives have been applied
in the footwear industry, composite flexible packaging industry, fabric laminates, glass bundles, ink adhesives, automotive interiors and other industries.
Waterborne polyurethane is also widely used in petroleum demulsifier, low cost, good demulsification effect, fast speed, non-toxic, easy to
use.
In addition, polyfluoroalkyl groups are grafted on the polyurethane backbone to make excellent waterproof, oil-proof and antifouling agents; Grafting halogens, phosphorus and other elements on its main chain can also be made into excellent flame retardant finishing agents
.

At present, waterborne polyurethane is more and more widely used in textile and printing and dyeing auxiliaries, such as as dyeing auxiliaries, coating printing binders, soft and anti-wrinkle finishing agents, antistatic and hydrophilic finishing agents, etc.
, which can improve its dyeing depth, fastness and other properties
of textiles.

Third, the development trend

According to preliminary statistics, there are hundreds of domestic waterborne polyurethane scientific research and production, manufacturers are mainly distributed in Zhejiang and Guangdong and other regions, relatively large include Beijing Linshi, Wenzhou Huanyu, Zibo Aodemei, Huangshan Meibang glue, Hefei Anda Kezhao fine chemical factory, etc
.
At present, the annual production capacity of domestic waterborne polyurethane is more than 30,000 tons, and the output exceeds 10,000 tons
.
Product quality has steadily improved
.

Over the years, in-depth and extensive research on waterborne polyurethane has been carried out at home and abroad, and the current development direction mainly includes the following aspects: the latest research methods are used to further explore the relationship between the structure and properties of ionic polyurethane; Using the latest electron microscopy technology, the structure and size of dispersed particles in waterborne polyurethane are studied; Develop new waterborne polyurethane varieties with excellent performance and high solid content to meet the application requirements of coatings and adhesives; Development of dispensing additives that meet the requirements of different applications
.

Waterborne polyurethanes are relative to solventborne polyurethanes
.
Because of the special properties of polyurethane, the variety of solvents that can dissolve polyurethane is very limited
.
From the perspective of environmental protection, waterborne polymer coatings are the most promising polymer application form in the 21st century, and will be more widely used
in industry and daily life.