Epi-halohydrin modified polyamines as mordant agents for alkaline rosin sizing.

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Hartong, Bradley H.
Deng, Yulin
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Many grades of paper have shifted from acid to alkaline production conditions. This change excludes the usage of traditional alum-rosin sizing chemistry. In some cases however, rosin sizing could prove beneficial if it could be used under neutral to alkaline paper making conditions. One effort toward this goal has been the use of epi-halohydrin modified polyamine/polyaminoamide in place of alum. The optimum sizing conditions, as well as the mechanism that modified polyamines/polyaminoamides use to size rosin, is investigated. Polyethyleneimine modified with epi-chlorohydrin was used in these studies. Rosin dosage was found to be the main variable that controlled the degree of sizing achieved. As the only hydrophobic material added, this was expected. In addition to rosin dosage, the polymer and pH had significant impacts on this sizing chemistry. Laboratory data shows that the synthesis procedure for and structure of polyethyleneimine-epi-cholohydrin (PEI-epi) impacts the degree of sizing achieved. Use of different modification techniques and degrees of modification illustrated several key factory regarding the polymer as a rosin sizing mordant. Prevention or removal of by-products from epi-chlorohydrin imporves the sizing efficiency of PEI-epi with rosin. A critical molecular weight of the PEI-epi was found to be important to sizing. Higher charge density on PEI-epi provides better the sizing efficiency. In addition to the polymer, other important factors where examined. The pH of the stock impacted the degree of sizing and permanency of the sizing achieved. Varying stock pH showed changes in sizing that are consistent with effects seen for rosin retention and of PAE as a wet strength agent. Low and high pH levels also caused reversion of the sizing effect. A pilot trial of the PEI-epi-rosin sizing chemistry was conducted at the Herty Foundation. The pilot trial shows that PEI-epi-rosin can reach the required level of sizing for linerboard. Trial results showed that calcium carbonate filled sheets could be sized by this chemistry. No significant impact on strength is seen from the sizing chemistry at the required dosage levels. As would be expected, addition of filler diminishes sheet strength. No sizing reversion was seen from any samples of this trial. Size reversion at low stock pH indicated that acid catalytic cleavage of an ester bond could have been occurring. Addition of acid or base to permanently sized sheets showed significant levels of reversion, similar to that seen for low stock pH sheets. This provides further supporting eviden ce for the formation and importance of an ester bond between rosin and PEI-epi. FTIR spectra were collected for model compounds to further examine the presence and importance of ester bonds. An ester bond was found to form at room temperature with aging or immediately with drying. Further, the ester bonds were found to decrease when the sample was subjected to acidic or basic environments. Solid state NMR was run to demonstrate the presence and importance of ester bonds to sizing in handsheets. Use of a [superscript 13]C labeled fatty acid showed that the ester bond peak dominated when sizing was present. After treatment with sodium hydroxide, the sizing disappeared and much of the ester bond signal shifted to a carboxylic acid or salt. Further solid state NMR of a non-reactive cationic polymer or a fully pre-reacted PEI-epi polymer shows retention of the fatty acid, but no ester bond and no sizing. The sizing mechanism of PEI-epi-rosin sizing appears to be connected to an ester bond formed during drying or with aging. While the amount of rosin retained controls the degree of sizing, retention alone is not enough to give sizing. The most effective pH for this sizing chemistry is near neutral, pH 6-8. FTIR and solid state NMR shows that an epichlorohydrin modified polyamine can form ester bonds with fatty acids in handsheets under conditions comparable to papermaking. The presence of residual acid or base in handsheets destroys the sizing effect achieved. Destruction of the sizing by addition of sodium hydroxide parallels the cleavage of many of the ester bonds present. PEI-epi appears to function as a mordant for rosin by creating an ester bond to anchor and help orient the hydrophobic portion of rosin.
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