Polyamine is a general term for a class of organic polymers that contain multiple amine groups (-NH₂, -NH-, or -N⁺<) along their molecular chain. These amine groups give polyamines their characteristic properties, primarily their positive charge (cationic nature) and reactivity.
Here's a comprehensive overview:
Backbone: Can be aliphatic (straight or branched carbon chains) or sometimes aromatic.
Functional Groups: Contain numerous amine functionalities. These can be:
Primary amines (-NH₂)
Secondary amines (-NH-)
Tertiary amines (-N<)
Quaternary ammonium groups (-N⁺<), which carry a permanent positive charge regardless of pH.
Charge: Most polyamines used industrially are cationic (positively charged). The charge density depends on the type and number of amine groups and the pH of the solution (except for quaternary amines, which are always charged).
Molecular Weight: Can range from relatively low (oligomers) to very high.
Polyamines can be categorized based on their origin and chemistry:
Synthetic Polyamines:
Condensation Polymers: Made by reacting epichlorohydrin with diamines (like ethylenediamine). These are the most common type in water treatment and papermaking. They often have a backbone with secondary and tertiary amines, and some quaternary groups.
Poly(aminoamide-epichlorohydrin): A specific, highly important subclass known for its wet-strength properties in paper.
Polyethyleneimine (PEI): A well-known, highly branched polymer with a very high density of primary, secondary, and tertiary amines. Available in linear and branched forms.
PolyDADMAC: While technically a polyquaternary amine, it's often discussed alongside other cationic polymers like polyamines.
Natural Polyamines:
Small molecule polyamines exist in living cells (e.g., spermine, spermidine, putrescine), playing roles in cell growth and nucleic acid stabilization. However, when discussing industrial applications, "polyamine" usually refers to the synthetic polymers.
Cationic Charge: Attracts and binds to negatively charged surfaces (anionic materials).
Water Solubility: Generally soluble in water, especially in their salt forms (e.g., hydrochloride).
Reactivity: Amine groups can react with various chemicals (epoxides, aldehydes, acids).
Water and Wastewater Treatment:
Coagulant/Flocculant: Used to remove suspended solids, turbidity, color, and organic matter by neutralizing negative charges on particles and forming flocs. Often used as an alternative to metal coagulants or PolyDADMAC.
Sludge Dewatering Aid: Improves the dewatering characteristics of sludge.
Paper Manufacturing:
Wet-Strength Agent: Poly(aminoamide-epichlorohydrin) resins form covalent bonds with cellulose fibers, significantly increasing the paper's strength when wet.
Dry-Strength Agent: Improves tensile and tear strength of dry paper.
Retention Aid: Helps retain fine particles and fillers in the paper sheet.
Pitch Control: Binds to sticky wood resins (pitch) to prevent deposits.
Textile Industry: Used as dyeing assistants, fabric softeners, and antistatic agents.
Oilfield Chemicals: Used in drilling fluids and as demulsifiers.
Personal Care Products: Found in hair conditioners and skin care products for their conditioning and film-forming properties.
Chelating Agents: Some polyamines can bind metal ions.
Charge Stability: Many synthetic polyamines (especially epichlorohydrin-diamine types) have tertiary amines whose charge depends on pH (more cationic at lower pH). PolyDADMAC has quaternary ammonium groups, giving it a permanent, pH-independent positive charge.
Structure: Polyamines often have more complex structures with secondary/tertiary amines, while PolyDADMAC has a simpler, regular structure with only quaternary groups.
Performance: PolyDADMAC generally has higher charge density. Polyamines might offer different floc characteristics or be preferred for specific applications like wet-strength in paper.
In essence, polyamine is a broad category of positively charged polymers valued for their ability to interact with negatively charged materials, making them indispensable in industries like water treatment and paper production.
