High-Performance Adhesive Formulations – Improved by Ultrasonic Dispersion
High-performance adhesives are composed from epoxy, silicone, polyurethane, polysulfide, or acrylic systems containing various (nano-)fillers and additives, which give the adhesive special performance such as bond strength, light weight, durability, heat-resistance, and sustainability. Efficient and reliable mixing is required to formulate high-performance adhesives. Ultrasonic dispersion and emulsification is used combine various components uniformly into homogeneous adhesive blends. Inline sonication blends even high viscous materials and high nano-filler loadings reliably and effective producing superior adhesives.
Ultrasonic High-Shear Forces for the Dispersion of High-Performance Adhesives
High-performance adhesives offer extraordinary bonding strength, durability and light weightiness. Depending on the final application, polymers, copolymers and multiple additives are formulated following elaborated recipes.
Ultrasonic High-Shear Mixers for Demanding Dispersion and Emulsion Applications
High-performance ultrasonic processors work like high-shear mixer. The extreme high-shear forces are generated by ultrasonic / acoustic cavitation and are ideal for batch and inline emulsification, dispersion, milling, deagglomeration and homogenization applications. Low to high solid concentrations and viscosities can be easily processed using ultrasonic inline dispersers.
Ultrasonic High-Shear Mixing of Nanomaterials in Adhesives
Nanomaterials such as carbon nanotubes (CNTs), metallic nanoparticles, nano-silica, nano-clays, nanofibres, and many other nano-sized particles are used in order to produce nanoreinforced polymers (nanocomposites). Nanoparticles are well known for their ability to alter mechanical properties (e.g., stiffness, elasticity), electrical properties (e.g., conductivity), functional properties (e.g., permeability, glass transition temperature, modulus), and fracture performance of thermoset polymer adhesives. Not only give nanomaterials special high-performance properties such as bond strength, durability, conduciveness, elasticity or heat-resistance; the addition of nano-structured particles can improve the barrier properties of polymers, too.
The high-shear forces of ultrasonically generated acoustic cavitation are well known for their capability to deagglomerate and disperse nano-particles and even to break primary particles (i.e., ultrasonic milling). When these ultrasonic forces are applied to polymeric systems containing nanoparticles and other fillers, a very uniform formulation is obtained. Ultrasonic dispersion is an energy-efficient method showing less energy consumption when compared to conventional shear-mixing methods such as high-shear blade mixers, impeller mixers, or mills.
- Reliable and efficient dispersion
- Superior overall mixing performance
- Rapid blending
- Increased bond strength
- Easily capable to process high viscosities
- Batch and in-line
- Risk-free formulation testing
- Linear scale-up
Kaboori et al. (2013) demonstrated that ultrasonication is an efficacious method to disperse layered structures of montmorillonite (MMT) and develop MMT-reinforced PVA adhesives. Ultrasonication was shown as reliable and efficient in dispersing nanoclay in PVA at low (1% and 2%) and high (4%) loadings.
The research team found that the “ultrasonic technique is very efficient in dispersing nanoclay especially at high loadings, contrary to the high shear speed mixer. High-speed mixing could disperse nanoclay in the PVA only at low loadings and increased bond strength of PVA in different conditions. High-speed mixing has some disadvantages: possible damage to PVA emulsion (because of strong shear force used during the mixing), high cost, and high energy consumption. By contrast, ultrasonication technique has minimum negative impact on PVA emulsion. Moreover, ultrasonication technique is economical as ultrasonic mixing could take place before production of PVA and the solution containing nanoclay can be added to PVA during the production process. By considering the results obtained from this paper and our previous work and by considering the advantages of ultrasonication technique over high-speed mixing, adding nanoclay to PVA in an industrial scale seems feasible and can be recommended to wood adhesive manufacturers.” (Kaboori et al., 2013)
Ultrasonic Degassing Effects in Adhesive Production
An additional advantage of sonication, which improves the formulation results significantly, is the degasification effect of the ultrasonic treatment. High speed mechanical stirring (e.g., high-shear blade mixers) produces a large number of gas bubbles in the mixture, which in some cases could even noticed due to the brightened color of the mixture. Ultrasonic high-shear mixing has the huge advantge that the sonication technique does not incorporate gases into the adhesive formulation, instead the ultrasound waves force already present gas bubbles to coalesce and to float to the liquid surface, from where the gas can easily be removed. Thereby, ultrasonication promotes the degasification and de-aeration of liquids and adhesive formulations. (cp. Shadlou et al., 2014)
High-Performance Ultrasonic Dispersers for Industrial Adhesive Formulations
Hielscher Ultrasonics designs, manufactures and distributes high-performance ultrasonic dispersers for heavy-duty applications such as the manufacturing of high-performance adhesives, highly filled resins and nanocomposites. Hielscher ultrasonicators are used world-wide for dispersing nano-materials into polymers, resins, coatings, and other high-performance materials.
Hielscher ultrasonic dispersers can be fed via various feeding streams adding various materials under controlled flow conditions into the cavitational mixing zone. Ultrasonic dispersers are reliable and efficient in processing low to high viscosities. Depending on the raw materials and size reduction target, ultrasonic intensity can be precisely adjusted.
In order to process viscous polymer pastes, nano-materials and high solid concentrations, the ultrasonic disperser must be capable to produce continuously high amplitudes. Hielscher Ultrasonics’ industrial ultrasonic processors can deliver very high amplitudes in continuous operation under full load. Amplitudes of up to 200µm can be easily run in 24/7 operation. The option to operate an ultrasonic disperser at high amplitudes and to adjust the amplitude precisely is necessary to adapt the ultrasonic process conditions to the formulation of high-performance adhesives, nano-reinforced polymer mixtures and nanocomposites.
Besides the ultrasonic amplitude, pressure is another very important process parameter. Under elevated pressures, the intensity of ultrasonic cavitation and its shear forces is intensified. Hielscher’s ultrasonic reactors can be pressurized thereby obtaining intensified sonication results.
Process monitoring and data recording are important for continuous process standardization and product quality. Pluggable pressure and temperature sensors wire to the ultrasonic generator for monitoring and controlling the ultrasonic dispersion process. All important processing parameters such as ultrasonic energy (net + total), temperature, pressure and time are automatically protocolled and stored onto a built-in SD-card. By accessing the automatically recorded process data, you can revise previous sonication runs and evaluate the process results.
Another user-friendly feature is the browser remote control of our digital ultrasonic systems. Via remote browser control you can start, stop, adjust and monitor your ultrasonic processor remotely from anywhere.
Contact us now to learn more about our high-performance ultrasonic dispersers and their applications in the production of high-performance adhesives and coatings!
The table below gives you an indication of the approximate processing capacity of our ultrasonicators:
|Batch Volume||Flow Rate||Recommended Devices|
|1 to 500mL||10 to 200mL/min||UP100H|
|10 to 2000mL||20 to 400mL/min||UP200Ht, UP400St|
|0.1 to 20L||0.2 to 4L/min||UIP2000hdT|
|10 to 100L||2 to 10L/min||UIP4000hdT|
|n.a.||10 to 100L/min||UIP16000|
|n.a.||larger||cluster of UIP16000|
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Literature / References
- Kaboorani, Alireza; Riedl, Bernard; Blanchet, Pierre (2013): Ultrasonication Technique: A Method for Dispersing Nanoclay in Wood Adhesives. Journal of Nanomaterials 2013.
- Shadlou, Shahin; Ahmadi Moghadam, Babak; Taheri, Farid (2014): Nano-Enhanced Adhesives. Reviews of Adhesion and Adhesives 2, 2014. 371-412.
- Zanghellini, B.; Knaack, P.; Schörpf, S.; Semlitsch, K.-H.; Lichtenegger, H.C.; Praher, B.; Omastova, M.; Rennhofer, H. (2021): Solvent-Free Ultrasonic Dispersion of Nanofillers in Epoxy Matrix. Polymers 2021, 13, 308.
- Hielscher, Thomas (2007): Ultrasonic Production of Nano-Size Dispersions and Emulsions. European Nano Systems 2005, Paris, France, 14-16 December 2005.
Facts Worth Knowing
High-Performance Adhesives and Glues
High-performance adhesives, glues and super-glues are used in manifold industries. An important advantage of high-performance adhesives is their extraordinary bonding strength and light weight. High-performance adhesives are widely used in construction, the automotive and aerospace sector, the manufacturing of medical equipment, commodity products, and footwear amongst many other goods.
Polymers are the base material used in adhesives. Commonly used polymers include polyesters, copolyester, copolyamide elastomers, polyols, and polyurethane (PU).
For each industry and application, special adhesives with adapted properties are available. For instance, water-based laminating adhesive systems are often used for food packaging, whilst thermoplastic polyurethane-based high-performance adhesives are widely applied in footwear. Based on the formulation technology, the high-performance adhesives can be divided into the four major segments of solvent-based, water-based, hot melt, and UV-curable. Ultrasonic dispersion and emulsification are used in the production of all these for high-performance adhesive types.