Rosin is acidic type sizing agent. In paper mill usually it is used as internal sizing agent. Rosin and its derivatives are cheap to produce and produced from regenerative raw materials. Hence these sizing agents are still a good number widely used of all wet-end sizing agents. Another source of “rosin” is ‘tall oil’ that is produced during kraft pulp manufacturing from softwood species. This rosin is a series of chemicals and one of the most important components of this type rosin is abietic acid, which is a partially unsaturated compound with one carboxyl group and three fused six-membered rings.
In the case of these sizing agents the degree of sizing can be controlled very easily. It has another advantage that the sizing effect is fully cured when the paper leaves the paper machine. Gum rosin is a natural product of pine trees.
The following rosin derivatives are used as sizing agent:
Fortified rosin size: Fortified rosin sizing agent is produced by the reaction with gum rosin and fumaric acid or maleic anhydride under suitable conditions. This is Diels-alder adduct which acts as a very effective sizing agent. The Diels-Alder adduct contains extra carboxyl groups and produces more proficient sizing response than the unreacted resin acids. It is common that the rosin which is extract from tall oil is fortified with fumaric acid. In this case some of the abietic acid and related compounds are converted into tricarboxylic species.
Cationic rosin size: Cationic rosin sizing agent is a effective sizing agent for paper. It decreases the consumption of additives as like alum, reduce environmental pollution by reducing discharge of acidic sewage, improve the paper quality as minimal acid is uses. Rosin soap size is a one kind of cationic rosin sizing agent.
Rosin soap size: It is sodium salts of resin acids. This rosin size is formed by neutralizing (saponifying) resin acids with NaOH or other sodium base, as like Sodium carbonate. There are different types rosin soap size are available such as extended size, paste size and dry size.
Free rosin: The carboxyl groups of resin acids are totally protonated form.
Extended size: A 50% neutralize solid product.
Dry size: A 100% neutralized dry rosin size product that dissolves easily in water.
Paste size: A 80% neutralized rosin size product.
Neutral Size Rosin: Neutral Size Rosin can be used in neutral conditions and this type rosin is suitable for the use of calcium carbonate as filler materials thus improving optical properties.
Function of rosin sizing agent: Aluminium resinate is the active component for rosin sizing agent. Aluminium sulphate or polyaluminium chloride is used after rosin sizing agent to obtain this reagent. Aluminium resinate oppose penetration the water into paper. Sizing effect can be attained by the electrostatic interactions with cellulosic surface.