What Is A Binder?
Definition
A binder is a substance that holds or binds materials together, promoting cohesion within unassembled or loosely assembled matter. It is a material used to join or consolidate fibers, plastics, rubbers, and other materials, fabricating articles or products. Binders consist of a backbone polymer to provide strength, fillers to occupy space between particles, and additives to adjust viscosity, lubricate, disperse particles, or induce wetting.
Composition and Types of Binders
Binders can be classified into organic and inorganic types. Organic binders are derived from animal, plant, or synthetic sources. Common components include:
- Backbone polymer: Polyethylene, polypropylene, ethylene vinyl acetate, polystyrene
- Fillers: Polyacetal, paraffin wax
- Additives: Stearates, stearic acid, magnesium stearate, phosphates, sulfonates
For inkjet printing, binders contain solvents to lower viscosity for easier jetting. Binders can be single-component or multi-component systems, such as a polymeric product of a carbohydrate reactant and a polyamine or a carbohydrate reactant and a nucleophile.
Properties of Binder
Physical Properties
Key physical properties that impact binder performance include:
- Viscosity and rheological properties during mixing/compaction
- Glass transitions from glassy to rubbery state upon water absorption
- Viscoelastic vs viscous flow behavior affecting granulation
Performance Attributes
Binders are designed to provide specific performance attributes such as:
- High mechanical strength and bond strength
- Resistance to aging, moisture, and corrosion
- Low water demand and shrinkage
- Barrier properties like fatty acid and liquid water resistance
Synthesis of Binder
Thermoplastic Binder Synthesis
- Mixing poly(lactic acid) and poly(ethylene glycol) to prepare a thermoplastic binder
- Adding ceramic particles and antioxidants to the thermoplastic binder to form an ink
Polysaccharide-based Binder Synthesis
- Reacting a polysaccharide (starch, dextrin, guar gum) with an amide like acrylamide
- Adding polymerization initiators (potassium persulfate, ammonium persulfate) to obtain a grafted polymer
- Contacting the grafted polymer with fillers (inorganic clays like bentonite) to get the composite binder
Lignin-based Binder Synthesis
- Forming an aqueous lignin-alkali composition
- Mixing with a polymerizable substance, crosslinking agent, and heating with a catalyst to produce the binder
- Adding a defoamer in the aqueous lignin step and/or the polymerization step
Binder Composition Synthesis
- Mixing predetermined amounts of thickener, pigment, additives, and fluid medium
- Optionally adding adhesion promoters and wetting agents
- Simple and environment-friendly process to roughen surfaces and bond with cementitious products
Uses & Benefits of Binder
Binders are widely used in various industries for binding and adhesive purposes. Some key applications and benefits include:
- Friction-modifying coatings: Binders enable precise and uniform application of coatings by mechanically controlling and metering the binder and filler, ensuring good control over coating thickness and binder-to-filler ratios. This optimizes the coating for desired friction performance.
- Granular fertilizers: Novel dual-purpose binder formulations can agglomerate dispersed particles into granules with increased hardness, roundness, and durability, while also serving as in-situ chelating agents for micronutrients.
- Additive manufacturing: Binders play a crucial role in direct ink writing of energetic materials, enabling high particle content (>80 vol%) while maintaining printability. Tunable binder viscosity and rheology are key for consistent line width and 3D object printing.
- Foundry industry: Organic resin-based binders are used to strengthen cores and molds, resulting in significant labor and energy savings, and higher productivity.
Application Case
| Product/Project | Technical Outcomes | Application Scenarios |
|---|---|---|
| Friction-modifying Coatings | Binders enable precise and uniform application of coatings, ensuring good control over coating thickness and binder-to-filler ratios, optimising the coating for desired friction performance. | Automotive and industrial applications requiring precise friction control and wear resistance. |
| Granular Fertilisers | Novel dual-purpose binder formulations can agglomerate dispersed particles into granules with increased hardness, roundness, and durability, while also serving as in-situ chelating agents for micronutrients. | Agriculture and horticulture, enabling efficient nutrient delivery and improved fertiliser handling. |
| Direct Ink Writing for Additive Manufacturing | Binders enable high particle content (>80 vol%) while maintaining printability, with tunable viscosity and rheology for consistent line width and 3D object printing. | Additive manufacturing of energetic materials, ceramics, and composites for aerospace, defence, and advanced manufacturing applications. |
| Foundry Core and Mold Binders | Organic resin-based binders strengthen cores and molds, resulting in significant labour and energy savings, and higher productivity. | Metal casting and foundry industries, enabling efficient and cost-effective production of complex metal components. |
| Multifunctional Epoxy Resins | Multifunctional epoxy resins with tailored properties can serve as binders, adhesives, and coatings, offering high strength, chemical resistance, and thermal stability. | Aerospace, automotive, and construction industries, providing durable and high-performance composite materials and coatings. |
Latest innovations of Binder
Sustainable and Renewable Binders
There is a growing trend towards developing sustainable and renewable binders to meet environmental and sustainability goals. Some key innovations include:
- Bio-based polyester binders derived from renewable resources like vegetable oils, providing strong bonding while being environmentally friendly.
- Carbohydrate-based binders are derived from reacting carbohydrates and acids, offering a formaldehyde-free alternative to traditional phenol-formaldehyde binders.
- Lignin-based binders utilizing lignin, a byproduct of the paper industry, as a renewable raw material for binder production.
High-Performance Binders
Innovations are focused on enhancing the performance and functionality of binders:
- Epoxy-based binders offering improved fracture toughness and permeability for liquid composite molding applications in industries like aerospace and automotive.
- Conductive binders incorporating conductive materials like carbon nanotubes or graphene for applications in energy storage devices and electronics.
- Pyridine-containing energetic binders providing higher energy output and reduced combustion velocity for nanoenergetic composites.
Binder Synthesis and Modification
Advances in binder synthesis and modification techniques enable tailored properties:
- Copolymerization and grafting techniques to modify binder properties like adhesion, flexibility, and water resistance.
- Pre-polymer synthesis methods to enhance initial tack and bonding strength of binders.
- Incorporation of additives like nanoparticles, fibers, or reactive monomers to improve mechanical, thermal, or electrical properties.
Application-Specific Binders
Binders are being developed for specific applications and industries:
- Low-VOC and solvent-free binders for paper-based packaging with improved oil and grease resistance, meeting consumer demands for safe and sustainable packaging [text].
- Binders for mineral wool and fiberglass insulation products with enhanced mechanical strength, curing speed, and aging resistance.
- Binders for lithium-ion battery electrodes with improved cycling stability, rate performance, and adhesion to current collectors.
These innovations in binders aim to address various challenges, including sustainability, performance, and application-specific requirements, driving the development of more advanced and specialized binder systems.
Technical challenges
| Sustainable and Renewable Binders | Developing binders derived from renewable resources like vegetable oils, carbohydrates, and lignin, providing strong bonding while being environmentally friendly and formaldehyde-free. |
| High-Performance Binders | Enhancing the performance and functionality of binders, such as improving fracture toughness, permeability, and conductivity for applications in industries like aerospace, automotive, and energy storage. |
| Multifunctional Binders | Designing binders with active functional groups to bind intermediates, maintain structural integrity, and facilitate ion transport, particularly for lithium-sulfur battery cathodes. |
| Low-Cost and Efficient Binders | Developing binders that are economically produced, have high curing speed at low temperatures, and can be used for efficient integrated operations in applications like agriculture. |
| Binders for Composite Materials | Utilizing binders to stabilize preforms, improve fracture toughness, and enable automated laying of dry fibers in the manufacturing of composite materials by liquid composite molding techniques. |
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