Amino resins in paper treatment: which performance attributes are improved by amino (urea/melamine) resin additives?

Introduction / Context:
Amino resins such as urea–formaldehyde (UF) and melamine–formaldehyde (MF) are used in paper and board to enhance wet strength and surface durability. The resins form crosslinks with cellulose or act as wet-strength agents within the fibre network, boosting performance in packaging and tissue grades.

Given Data / Assumptions:

• Additives are amino resins added during wet end or applied at the size press.
• Desired properties include wet tear/burst strength, folding endurance, and wet rub resistance.
• Application conditions allow adequate cure/retention.

Concept / Approach:
Under acidic conditions and appropriate cure, UF/MF resins form a network that resists fibre–fibre debonding when re-wetted. This increases wet tensile/burst metrics and helps maintain integrity under folding and rubbing. Melamine-modified systems can further improve moisture and chemical resistance.

Step-by-Step Solution:
Identify property targets relevant to wet-strength chemistry.Recognise amino resins as standard wet-strength agents.Conclude that all listed properties improve.

Verification / Alternative check:
Paper testing (e.g., wet tensile, Mullen burst, MIT folding) shows clear gains after amino resin treatment compared to untreated controls.

Why Other Options Are Wrong:
Each single-property option is incomplete; amino resins improve the full set when properly formulated.

Common Pitfalls:
Confusing internal wet-strength agents with surface sizes; both can be used, but internal addition is key for through-thickness wet strength.

Final Answer:
All (a), (b) & (c)