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Surface chemistry of paper

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Surface chemistry of paper

The surface chemistry of paper is responsible for many important paper properties, such as gloss, waterproofing, and printability. There are many components that are used in the paper-making process. The interactions between these components are responsible for creating the properties of the paper. The types and quantities of ingredients used can be adjusted to reach the desired properties. In order to understand why paper has certain properties, one must first understand the chemistry of the paper.

Paper Components and Their Interactions

Pigment and Dispersion Medium

Coating components are subject to particle-particle, particle-solvent, and particle-polymer interactions.[1] Van der Waals forces, electrostatic repulsions, and steric stabilization are the reasons for these interactions.[2] It is important to point out the characteristics of adhesion and cohesion between the components that form the base coating structure. Calcium carbonate and kaolin are commonly used pigments in paper production.[1][2] Pigments support a structure of fine porosity and form a light scattering surface. The surface charge of the pigment plays an important role in dispersion consistency. The surface charge of calcium carbonate is negative and not dependent on pH, however it can decompose under acidic conditions.[3] Kaolin has negatively charged faces while the charge of its laterals depend on pH, being positive in acidic conditions and negative in basic conditions with an isoelectric point at 7.5.[1] The equation for determining the isoelectric point is as follows:

                                            pI = +\gamma_{\mathrm{LG}}\cos{\theta_\mathrm{c}}=\gamma_{\mathrm{SG}}\, 

where \gamma_{\mathrm{SL}} is the interfacial tension between the solid and the liquid, \gamma_{\mathrm{LG}} is the interfacial tension between the liquid and the vapor, and \gamma_{\mathrm{SG}} is the interfacial tension between the solid and the vapor.

An ideal oleophilic surface would have a contact angle of 0° with oil, therefore allowing the ink to transfer to the paper and be absorbed. The hydrocarbon plasma coating provides an oleophilic surface to the paper by lowering the contact angle of the paper with the oil in the ink. The hydrocarbon plasma coating increases the non-polar interactions while decreasing polar interactions which allow paper to absorb ink while preventing dampening water absorption.[7]

Applications

Printing quality is highly influenced by the various treatments and methods used in creating paper and enhancing the paper surface. Consumers are most concerned with the paper-ink interactions which vary for certain types of paper due to different chemical properties of the surface.[8] Inkjet paper is the most commercially used type of paper. Filter paper is another key type of paper whose surface chemistry affects its various forms and uses.

Inkjet Printing Paper

Co-styrene-maleic anhydride and co-styrene acrylate are common binders associated with a cationic starch pigment in Inkjet printing paper.[8] Table 1 shows their surface tension under given conditions.

Compound Monomer Proportion pH Surface Tension (mN/m)
Cationic Starch - 5.0 32.9
Co-styrene-maleic anhydride 3:1 7.6 38.51
Co-styrene acrylate 3:4 4.3 49.99

There have been several studies that have focused on how the paper printing quality is dependent on the concentration of these binders and ink pigment. Data from the experiments are congruent and stated in Table 2 as the corrected contact angle of water,[9] the corrected contact angle of black ink,[8] and the total surface energy.[10]

Sample Sizing Formulation (% w/w) Contact Angle of Water (˚) Contact Angle of Black Ink (˚) Total Surface Energy (mN/m)
1 no surface treatment 103.1 81.7 39.5
2 100% cationic starch 39.2 36.1 51.25
3 80% cationic starch/ 20% co-styrene-maleic anhydride 80.5 65.2 38.39
4 80% cationic starch/ 20% co-styrene acrylate 60.2 60.5 42.39

The contact angle measurement has proven to be a very useful tool to evaluate the influence of the sizing formulation on the printing properties. Surface free energy has also shown to be very valuable in explaining the differences in sample behavior.[8]

Filter Paper

Various composite coatings were analyzed on filter paper in an experiment done by Wang et al.[11] The ability to separate homogenous liquid solutions based on varying surface tensions has great practical use. Creating superhydrophobic and superoleophilic filter paper was achieved by treating the surface of commercially available filter paper with hydrophobic silica nanoparticles and polystyrene solution in toluene.[11] Oil and water were successfully separated through the use of the filter paper created with an efficiency greater than 96%. In a homogenous solution the filter paper was also successful in separating the liquids through differentiating for surface tensions. Although with a lower efficiency, aqueous ethanol was also extraced from the solution when tested on the filter paper.[11]

See also

References

  1. ^ a b c d e Fardim, Pedro (2000). "Paper and Surface Chemistry Part 2- Coating and Printability". Institute of Quimica: 1–13. 
  2. ^ a b c Fardim, Pedro (2000). "Paper and Surface Chemistry Part 1- Fiber Surface and Wet End Chemistry". Institute of Quimica: 1–14. 
  3. ^ Gaudreault, Rodger; Weitz (September 2009). "The Structure and Strength of Flocs of Precipitated Calcium Carbonate Induced By Various Polymers Used in Paper-making". Fundamental Research Symposium 14: 1193–1219. 
  4. ^ Granier (1994). "Adhesion of latex particles on inorganic surfaces". Tappi J 77 (5): 419. 
  5. ^ a b c Hubbe, Martin. "Cationic Starch". 
  6. ^ a b Hubbe, Martin. "R&D Chemicals: How they Impact Papermaking". 
  7. ^ a b c d e Pykonen, M; Johansson, K., Dubreuil, M., Strom, G., (2010). "Evaluation of Plasma-Deposited Hydrophobic Coatings on Pigment-Coated Paper for Reduced Dampening Water Absorption". Adhesion Science and Technology 24: 511–537.  
  8. ^ a b c d Moutinho, Isabel (15 July 2007). "Impact of Surface Sizing on Inkjet Printing Quality". Industrial and Engineering Chemistry Research 46: 6183–6188.  
  9. ^ Gruyter, Walter (16 December 2009). "Effect of surface sizing on the surface chemistry of paper containing eucalyptus pulp". Holzforschung 63: 282–289.  
  10. ^ Moutinho, Isabel (27 September 2011). "Paper Surface Chemistry as a Tool to Improve Inkjet Printing Quality". BioResources 6 (4): 4259–4270. 
  11. ^ a b c Wang; Li (March 2010). "Filter paper with selective absorption and separation of liquids that differ in surface tension". Applied Material Interfaces 2 (3): 677–683.  
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