4 DISCUSSION

The combination of many kinds of variables was necessary because of the natural demands of solving the problem of conserving documents from attack by fungi. Also to be taken into consideration is the added complexity of considering the inks, dyes, and pigments that form part of the documents.

Sterilization of the samples after applying the polymers was necessary to ensure that only test organisms and no other contaminants interacted with the paper.

To evaluate the protective effect of the sizes after the fungal attack, it was necessary to submit the samples to an aseptic step, though one not equal to fumigation. This procedure helped us to handle the attacked material with some confidence and served as a precaution against dispersal of spores that could enter researchers' respiratory tract. These aseptic steps influenced the results of zero-span tensile strength, having a tendency to reinforce this property of the paper. This had little effect on the final results.

Results of zero-span tensile strength were analyzed with Statgraphics Version 7. The ANOVA results summarized in table 3 show that the factors of strain and coating have significant differences in effect on zero-span tensile strength in the different variations. There is also an interaction between the two factors because the protective effect of each treatment depends on the strain that is being tested.

Figure 4, in which the “x” axis represents the kind of coating and each group of points shows a different kind of strain, demonstrates clearly that chitosan salt coatings offer more protection than cellulose ether coatings do. But important deterioration occurred in both, probably as a consequence of uneven coating. The graph also shows that the reference samples sized with cellulose ethers have higher zero-span tensile strength than reference samples sized with chitosan salts.

We do not know the protection mechanism of chitosan on paper. To help clarify this mechanism, future testing to evaluate the toxicity of chitosan on specific strains of fungi is needed. It is possible that protection is created by the formation of a barrier shielding the fibers against degradation, and we cannot discard the possibility of a true inhibition.

Chitosan salts AQ, BQ, and PQ reacted so similarly that it is not possible to distinguish the margin of difference.

Cellulose ethers also reacted very similarly, although HPMC and MC have more similarity in their properties and reaction than they do with CMC, even though the three products function almost equally.

However, the cellulose ether coatings exhibited little protection. Apparently CMC was more resistant to fungal attack than MC and HPMC were (see figs. 2, 4).

Dobroussina et al. (1996) mention that in papers coated with some types of cellulose ethers, micro-organism damage can occur. Although the development time is much slower than in the uncoated paper, it is thought that the attack occurs only when there are microscopic holes on the coated surface, which generally happens when one polymer is applied in solution or melted. Maybe if there were more viscosity (see Ponce-Jim�nez et al. 2002), cellulose ethers would be more likely than the chitosan salts to form an irregular film with large pores.

However, it is enormously important to consider the differences between fungi strains. Obviously none of the materials examined have the capacity to inhibit all kinds of fungi. And there is a common association between fungi and bacteria in the deterioration of materials like paper with a low nutrient content (Mandels and Reese 1960). Also, the additives often increase the nutritive value of the material, reinforcing the fungal attack. Even though short-term protective effects can be gained, there is no guarantee of long-term effectiveness for chitosan, for which it will be necessary to design new investigations.

It was observed that the strains with higher cellulolytic activity were, from high to low, Chaetomium britannicum, Chaetomium globosum, and Aspergillus terreus.

The analysis of figure 4 led to the following conclusions: the Alternaria alternata strain shows notable variables according to the type of chitosan salt or cellulose ether applied, being more aggressive to the control, HPMC, MC, and CMC than to chitosan salts. The strain that caused the most damage was Chaetomium globosum.