chemistry

Surface chemistry of paper

Surface chemistry of paper is a chemistry topic covered in the lgStudy science library. This page brings together a partial reference excerpt, illustrations, worked examples, real-world applications and a short study plan, so you can understand Surface chemistry of paper rather than just read about it. In short: The surface chemistry of paper is responsible for many important paper properties, such as gloss, waterproofing, and printability. Many components are used in the paper-making process that affect the surface.

Key takeaways

Surface chemistry of paper belongs to chemistry; place it in that map before memorising details.
Learn the definition first, then one example that makes the definition concrete.
Connect Surface chemistry of paper to a quantity you can measure, compute or draw — that is where exam questions come from.
Reproduce the core statement of Surface chemistry of paper from memory before moving on to harder problems.

Reference excerpt

The surface chemistry of paper is responsible for many important paper properties, such as gloss, waterproofing, and printability. Many components are used in the paper-making process that affect the surface.

Pigment and dispersion medium Coating components are subject to particle-particle, particle-solvent, and particle-polymer interactions. Van der Waals forces, electrostatic repulsions, and steric stabilization are the reasons for these interactions. Importantly, the characteristics of adhesion and cohesion between the components form the base coating structure. Calcium carbonate and kaolin are commonly used pigments. 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. 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. The equation for determining the isoelectric point is as follows:

p I = p K a + p K b 2 {\displaystyle pI={{pKa}+{pKb} \over 2}}

In the papermaking process, the pigment dispersions are generally kept at a pH above 8.0.

Pigments, binders, and co-binders

Binders promote the binding of pigment particles between themselves and the coating layer of the paper. Binders are spherical particles less than 1 µm in diameterr. Common binders are styrene maleic anhydride copolymer or styrene-acrylate copolymer. The surface chemical composition is differentiated by the adsorption of acrylic acid or an anionic surfactant, both of which are used for stabilization of the dispersion in water. Co-binders, or thickeners, are generally water-soluble polymers that influence the paper's color viscosity, water retention, sizing, and gloss. Some common examples are carboxymethyl cellulose (CMC), cationic and anionic hydroxyethyl cellulose (EHEC), modified starch, and dextrin.

Sizing

In sizing, the strength and printability of paper is increased. Sizing also improves the hydrophilic character, liquid spreading, and affinity for ink. Starch is the most common sizing agent. Cationic starch and hydrophilic agents are also applied, including alkenyl succinic anhydride (ASA) and alkyl ketene dimers (AKD). Cationic starch increases strength because it binds to the anionic paper fibers. The amount added is usually between ten and thirty pounds per ton. When starch exceeds the amount the fibers can bind to, it causes foaming in the production process as well as decreased retention and drainage.

Surface modification

Plasma surface modification Surface modification makes paper hydrophobic and oleophilic. This combination allows ink oil to penetrate the paper, but prevents dampening water absorption, which increases papers printability. Three different plasma-solid interactions are used: etching/ablation, plasma activation, and plasma coating. Etching or ablation is when material is removed from the surface of the solid. Plasma activation is where species in the plasma like ions, electrons, or radicals are used to chemically or physically modify the surface. Lastly, plasma coating is where material is coated to the surface in the form of a thin film. Plasma coating can be used to add hydrocarbons to surfaces which can make a surface non-polar or hydrophobic. The specific type of plasma coating used to add hydrocarbons is called plasma enhanced chemical vapor deposition process or PCVD.

Contact angle An ideal hydrophobic surface would have a contact angle of 180 degrees to water. This means that the hydrocarbons lie flat against the surface creating a thin layer and preventing dampening water absorption. However, in practice it is fine or even preferred to have a low level of dampening water absorption because of a phenomenon that occurs when water settles at the surface of paper. This phenomenon is when ink is unable to transfer to the paper because of the water layer at the surface. The contact angle value for hydrocarbons on a rough pigment-coated paper can be found to be approximately 110° through a contact angle meter. The Young's equation can be used to calculate the surface energy of a liquid on paper. Young's equation is:

γ S L + γ L G cos ⁡ θ c = γ S G {\displaystyle \gamma _{\mathrm {SL} }+\gamma _{\mathrm {LG} }\cos {\theta _{\mathrm {c} }}=\gamma _{\mathrm {SG} }\,}

… excerpt ends here. Continue reading the full article.

Illustrations

Surface chemistry of paper: The molecular structure of cationic starch. The repeating unit of starch is derived from glucose interconnected with glycosidic bonds. — The molecular structure of cationic starch. The repeating unit of starch is derived from glucose interconnected with glycosidic bonds.

Worked examples

Example 1 — a first encounter with Surface chemistry of paper

Start with the simplest possible case. Write down what Surface chemistry of paper claims or describes in one sentence, then invent the smallest concrete situation in which that sentence is true. In chemistry, the smallest case is usually a single object, a single equation or a single measurement. Check that every symbol or term in your sentence has a meaning in that case.

Example 2 — changing one variable

Take the situation from Example 1 and change exactly one quantity: double it, halve it, or set it to zero. Predict what should happen to Surface chemistry of paper before you calculate. Comparing your prediction with the result is the fastest way to find out whether you understand the idea or only the words.

Example 3 — an exam-style question

Typical questions about Surface chemistry of paper ask you to (a) state it precisely, (b) apply it to given data, and (c) explain a limitation. Practise writing all three answers in under five minutes; the third part is what separates a full-mark answer from an average one.

Applications of Surface chemistry of paper

In research: Surface chemistry of paper appears in chemistry research whenever the underlying quantities have to be modelled precisely. Papers usually cite it as a starting assumption and then explore where it breaks down.
In technology and industry: Engineering practice reuses Surface chemistry of paper in design rules, simulations and safety margins. Knowing the idea lets you read a specification sheet and understand why the numbers look the way they do.
In the classroom: Surface chemistry of paper is common in secondary-school and first-year university syllabi. It links to neighbouring topics Paper, Surface science, so understanding it makes those chapters shorter.
In everyday life: Look for Surface chemistry of paper outside the textbook — in sport, cooking, traffic, electronics or the sky above you. An example you found yourself is remembered far longer than one you were given.

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How to study Surface chemistry of paper in 20 minutes

Read the reference excerpt below once, without taking notes.
Close the page and write down what Surface chemistry of paper means in your own words.
Compare your version with the excerpt and mark what you missed.
Work through the three examples above with pen and paper.
Explain Surface chemistry of paper out loud to somebody else — or to Teacher Smith in the lgStudy chat.

Frequently asked questions

What is Surface chemistry of paper in simple terms?

Why does Surface chemistry of paper matter?

Because it connects several chemistry ideas at once: it gives you a definition you can apply, a quantity you can calculate, and a way to check whether a result is plausible.

How should I study Surface chemistry of paper?

Read the excerpt, restate it from memory, then work through the examples and applications listed on this page. The five-step study plan above takes about twenty minutes.

What does this page cover?

It gives you a compact reference excerpt plus original lgStudy explanations, examples, applications and study material on Surface chemistry of paper.