Glyoxal and glutaraldehyde behave very differently for improving wet strength of paper. It is found that glyoxal is very efficient for improving temporary wet strength of paper without the presence of a catalyst and exposure to elevated temperatures. When a metal salt, such as Zn(NO 3 ) 2 , is used as a catalyst and the curing temperature is increased, the durable wet strength of glyoxal-treated paper increases at the expense of its flexibility, as shown by reduced stretch and folding endurance. Glutaraldehyde is not able to provide any improvement in wet strength to paper, even under high curing temperatures, provided no catalyst is used. With the aid of a metal salt catalyst, glutaraldehyde imparts excellent durable wet strength to paper without significantly sacrificing folding endurance, and the wet strength of glutaraldehydetreated paper increases steadily as curing temperature increases. The different behavior of glyoxal and glutaraldehyde may be attributed to their different reactivity toward cellulose.

Two bifunctional aldehydes (i.e., glyoxal and glutaraldehyde) are used as the crosslinking agents to improve paper wet strength in the presence of fully hydrolyzed poly(vinyl alcohol) (PVA) as a co-reactant. These bifunctional aldehydes alone improve paper wet strength but diminish its folding endurance. The use of PVA as a coreactant not only improves paper wet strength but also increases its dry strength and folding endurance. Glutaraldehyde is able to impart much higher levels of wet strength to the treated paper than glyoxal when a catalyst is present. The wet strength of the treated paper increases as the amount of PVA added is increased, and it also increases as the molecular weight (M w ) of the PVA increases. The data suggest that the reaction between glutaraldehyde and PVA promotes the formation of interfiber crosslinking, thus improving the wet strength without diminishing the flexibility of the treated paper. The use of a catalyst is critical to achieve high levels of durable wet strength of the treated paper. We studied the effects of different Lewis acids as the catalysts for crosslinking of pulp cellulose by glutaraldehyde and found that Zn(NO 3 ) 2 is the most effective one.

Polycarboxylic acids have been used as crosslinking agents for wood pulp cellulose for improving paper wet strength. Our previous research showed that lowmolecular-weight polymeric carboxylic acids are effective in improving paper wet strength retention and reducing its flexibility. In this research, we compared two polymeric carboxylic acids, that is, poly(maleic acid) (PMA) with M n of 800 and poly-(methyl vinyl ether-co-maleic acid) (PMMA) with M n of 1,130,000 for improving paper wet strength. The kraft paper sheets were treated at a 2% acid level and cured at different temperatures. The dry strength, wet strength, and folding endurance of the treated sheets were measured. We found that PMA and PMMA have comparable effectiveness in improving paper wet strength and wet stiffness. However, the treatment with PMA increases paper brittleness and severely diminishes paper folding endurance, whereas the treatment with PMMA increases both the dry strength and folding endurance by enhancing the paper's toughness. This striking difference in the performance of the treated paper is attributed to the different nature of the crosslinkages formed on the sheets.

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A compact MIMO antenna using a decoupling network for 4G USB dongle application is proposed. The proposed MIMO antenna consists of two parallel folded monopole antennas with the length of 100 mm and a decoupling network. To improve the isolation characteristic at the LTE band 13, a decoupling network was added between the two antennas placed close to each other. The decoupling network is simple and compact and consists of two sections of transmission line, a shunt reactive component and quarter‐wavelength jointed shorting structure. The proposed MIMO antenna has the isolation less than −15 dB at the LTE band 13 and the ECC is lower than 0.4 over the whole LTE band. © 2010 Wiley Periodicals, Inc. Microwave Opt Technol Lett 52:2551–2554, 2010; View this article online at wileyonlinelibrary.com. DOI 10.1002/mop.25551