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water. Therefore, water immersion time is a critically important parameter in testing the wet strength of such paper grades. T456 om-3 details the specimen preparation, process of examination, and method of data collection and calculation. The suggested immersion time ranges from 5 to 40 s for easily saturated paper products, such as tissue, and from 2 to 24 h for other grades, such as paperboard, which can be difficult to saturate. These suggested periods of time are intended to make sure that the paper samples are fully saturated by water so that the variation in strength is less than 10%. On the other hand, the varying conditions of sample immersion time in water in the T456 om-3 method can lead to inconsistency in the wet strength results. We have reviewed relevant published literature regarding the wet strength of paper and found that the immersion time in water for wet strength examination of paper varied greatly, namely, 2 s, 5 s, 1 min, 100 s, 5 min, 10 min, 30 min, 1 h, 2 h, 12 h, 24 h, and overnight (Yang HWDO 1996; Yang and Xu 1998; Lund and Felby 2001; Xu HWDO 2004; Vander Wielen HWDO 2005; Khampan HWDO 2010; Sun HWDO 2010; Aracri HWDO . 2011; Chen HWDO 2013; Su HWDO 2014; Ichiura HWDO 2017). Another important factor affecting the paper wet strength, which has been neglected in the literature, is the dryness of paper specimens just before testing. It is well known that the initial dryness determines the paper strength of not only wet web but also rewetting phenomena (Hamzeh HWDO 2013). A Suggestion to Improve the Determination of Wet Strength of Paper Based on the above discussion, we suggest to report the wet strength of paper as functions of the immersion time and initial dryness of paper. As an option, the wet strength may be expressed as a function of immersion time and the dryness of paper specimens. For instance, there could be a 3 D plot, in which the X-axis corresponds to the immersion time, the Y-axis is for the initial dryness of the paper specimen, and the Z-axis is for the measured wet strength. In this way, the temporary wet strength of paper may fully convey the specific information, which can also have direct comparisons with other results in the literature. Different immersion times in water for the sample can bring about undesired experimental errors. The inclusion of dryness of the paper specimen in the reported results also can give important information related to how the dryness of the sample affects the measured wet strength. Acknowledgements The authors would like to acknowledge support from Science and Research Programs of Education Department of Jilin Provence of P.R.C. (No. 201684). References Cited Aracri, E., Vidal, T., and Ragauskas, A. J. (2011). “Wet strength development in sisal cellulose fibers by effect of a laccase –TEMPO treatment,” &DUERK\GUDWH3RO\PHUV 84(4), 1384-1390. DOI: 10.1016/j.carbpol.2011.01.046 Chen, Z., Zhang, H., Song, Z., and Qian, X. (2013). “Combination of glyoxal and chitosan as the crosslinking system to improve paper wet strengt h,” %LR5HVRXUFHV 8(4), 6087-6096. DOI: 10.15376/biores.8.4.6087-6096 Hamzeh, Y., Sabbaghi, S., Ashori, A., Abdulkhani, A., and Soltani, F. (2013). “Improving wet and dry strength properties of recycled old corrugated carton (OCC)
Chen et al. (2018 ). “ Rethinking determination wet strength ,” B io R esources 13(2), 2184-2186. 2185
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