What is wet strength in paper?

The wet strength of paper and paperboard is a measure of how well the web of fibers holding the paper together can resist a force of rupture when the paper is wet. Wet strength is routinely expressed as the ratio of wet to dry tensile force at break.[1]

Are you interested in learning more about Wet Strength Paper? Contact us today to secure an expert consultation!

With combined board such as corrugated fiberboard or with laminations, wet strength also includes the ability to stay intact under humid or wet conditions. Wet strength adhesives are often needed.

Mechanism

[

edit

]

The cellulose fibreweb of paper is mainly held together by hydrogen bonds. These are dependent on physical contact between the fibres and can be broken by wetting of the fibres. The residual strength of a wetted paper can be less than 10% of the original strength.[1]

Various techniques, such as refining of the pulp and wet pressing on the paper machine can be used to reduce the strength loss of the paper upon wetting. To improve the wet strength it is common to use chemicals. The use of chemicals can retain as much as 10% to 30% of the original dry strength of the paper.[1] The wet strength chemicals may improve the dry strength of the paper as well.

A Japanese research team found that the effect of humidity on cardboard differs depending on how it is dispersed. Ultrasonic mist reduces the wet strength of cardboard more so than nano-mist.[2]

Wet strength chemicals

[

edit

]

Wet strength chemicals improve the tensile properties of the paper both in wet and dry state by crosslinking the cellulose fibres with covalent bonds that do not break upon wetting.

Wet strength development should not be confused with sizing, the first representing the strength of the paper once wet, the latter being the speed and amount of water absorbed by the paper. Normal wet strength resins are: urea-formaldehyde (UF), melamine-formaldehyde (MF) and polyamide-epichlorohydrin (PAE).

Neutral sizing agents are alkylketene dimers (AKD) and alkenylsuccinic anhydride (ASA).

Coatings

[

edit

]

Sometimes wet strength can be obtained by curtain coating a polymer onto a paper or paperboard. Laminating a plastic film is also a method of providing wet strength.

Contact us to discuss your requirements of Aluminized Paper Exporter. Our experienced sales team can help you identify the options that best suit your needs.

Applications

[

edit

]

A wide range of paper materials are wet strengthened:

Environmental considerations

[

edit

]

Recycling of wet strengthened paper requires higher intensity reworking conditions in the re-pulping process to break the fibre web. Some wet strength papers are not considered recyclable.

References

[

edit

]

1. a b cNeimo, Leo, ed. (1999). "13". Papermaking Chemistry. Papermaking Science and Technology. Vol. 4. Helsinki, Finland: Fapet OY. pp. 289–301. ISBN 952-5216-04-7.

2. ^Hung, Duong Van; Nakano, Yusuke; Tanaka, Fumihiko; Hamanaka, Daisuke; Uchino, Toshitaka (30 November 2010). "Preserving the strength of corrugated cardboard under high humidity condition using nano-sized mists". Composites Science and Technology. 70 (40): 2123–2127. doi:10.1016/j.compscitech.2010.08.011.

AR Metallizing use the brand name RotoFLEX® for our wet-strength paper line.  In addition to different basis weights (grammages) there are other differences in our RotoFLEX® papers that usually are related to specific requirements of the end users. Usually the end users are breweries or wineries, but we also support a variety of different beverage producers (sparkling water brands, for example). 

The term 'wet-strength' itself indicates that the base paper before metallizing has been manufactured with a chemical that improves the bonding strength of the wood fibers when they have become completely wet in water.  The wet strength chemical has little effect on properties of the paper when it is dry, but when wet the paper is stronger and resists breaking, tearing, and damage from rubbing.  The most common way to measure the wet strength of paper is to test the tensile strength on an Instron-type machine, measuring strips when dry and also after soaking in water for five minutes.

Want more information on holographic paper for printing? Feel free to contact us.