Flexible cyanoacrylates

Polymeric materials are commonly used for bonding materials. Impact or contact adhesives are mainly based on highly crystalline polychloroprene (Neoprene), NR latex is used as a flexible adhesive very suitable for use with fabrics. Rigid adhesives based on materials such as polystyrene cement, epoxy resin or cyanoacrylates are suitable for bonding of rigid materials. The bond is provided by intramolecular forces between the adhesive and the adherend. Adiabatic... 

Polycyanocrylate - 2-Octyl-cyanoacrylate plasticized and self-stabilized is the slower, but slightly more flexible (octyl- vs. ethyl-substituent group) ionically curing adhesive that is catalyzed by weak bases including water. The liquid and nonsolvated DermabondR product forms a continuous film in -3-5 min that is continuous and very adherent to tissue. 

The modification of cyanoacrylate with other polymers and/or plasticizers provided more flexible adhesives, but the lack of bond and disbondment from excessive moisture continued to float off the adhesive without making firm contact with the tissue. 

The value of Fn was determined by 1H NMR spectroscopy and found to be close to unity. By essentially the same method, bifunctional and trifunctional cyanoacrylate functional PIBs have also been prepared. Anionic polymerization of CA-PIB with N,N-dimethyl-p-toluidine as initiator in solution resulted in high MW product (Mn 35,000 gmol ) [107]. Anionic copolymerization of difunctional and trifunctional PIB yielded clear flexible films with low sol fraction. The... 

Many cyanoacrylates give rather rigid bonds which may in consequence be brittle and not able to resist peeling forces. However, in recent years more flexible toughened grades have been developed for applications in which resistance to peeling is required. 

Reversion is usually much faster in flexible materials because water permeates them more easily. Hydrolysis has been seen in certain epoxy, polyurethane, and cyanoacrylate adhesives. The reversion rate also depends on the type and amount of catalyst used in the formulations and the degree of crosslinking. Best hydrolytic properties are obtained when the proper stoichiometric ratio of base material to catalyst is used. 

Tissue adhesives are formulated from cyanoacrylate compounds such as bucrylate, enbucrilate, or mecry-late which polymerize in an exothermic reaction on contact with a fluid or basic substance to form a strong, flexible, and waterproof bond. They are synthesized by reacting formaldehyde with alkyl cyanoacetate to obtain a prepolymer, which may be depolarized to a liquid monomer by heat. This monomer may then be modified by altering the alkoxycarbonyl (-COOR) group of the molecule to give compounds of different chain lengths. 

A cyanoacrylate with a flexible side chain to yield a more pliable polymer than those of alkyl cyanoacrylate without compromising adhesive joint strength — for Ihis, alkoxyalkyl cyanoacrylates were selected to meet the minimum compliance required for the resulting polymer. 

VI. IMPROVED COMMERCIAL CYANOACRYLATE COMPOUNDS A. New Flexible Cyanoacrylates... 

New cyanoacrylate compounds exhibit good adhesion to various plastics and elastomeric surfaces, such as Mylar, copper foil, and vinyl films. These products show better impact resistance and good flexibility compared to standard cyanoacrylates, good resistance to cracking under flexing or bending, and a longer open time than that of standard products. 

Assemblies joined with cyanoacrylate adhesives exhibit good long-term durability, particularly when the materials are somewhat flexible, such as rubbers and most plastics (see Fig. 7). Bonded lap shear specimens have been aged outdoors for 7 years with good retention of strength (see Table 8). 

Cyanoacrylates have shown themselves well in permanent outdoor assemblies as well as in temporary manufacturing aids. They are safe, convenient materials to incorporate in plant operations. New developments in technology have improved moisture resistance, setting times, gap filling, clarity, high-temperature resistance, and flexibility, and most recently, cyanoacrylates have become less surface sensitive. 

The main reason for the use of plasticizers in formulations is to increase flexibility. More extensive stu has been conducted with dioctyl phthalate, DOP, where appearance, curing time, film formation, flexibility and durability have been evaluated for n-butyl cyanoacrylates containing from 15 to 50 wt% plasticizer. When DOP was at a 35 wt% or above, no film was formed. With the plasticizer at 15 wt%, flexibility and durabihty suffered. A 20-25 wt% range has produced the best overall performance. 

Rigid polyvinyl chloride can be easily bonded with epoxies, urethanes, cyanoacrylates, and thermosetting acrylics. Flexible polyvinyl chloride parts present a problem because of plasticizer migration over time. Nitrile adhesives are recommended for bonding flexible polyvinyl chloride because of compatibility with the plasticizers used. Adhesives that are found to be compatible with one particular polyvinyl chloride plasticizer may not work with another formulation. Solvent cementing and thermal welding methods are also commonly used to bond both rigid and flexible polyvinyl chloride parts. 

A new primer (see Primers for adhesive bonding) has been developed that enables a cyanoacrylate to be used to bond polyolefins. The primer is applied to one surface, adhesive to the other - the bond is virtually instantaneous. This will allow the designers flexibility in choice of plastics, enabling less costly polyolefins to be selected. 

NOR HALS also improve the outdoor weathering of flexible PVC and are used as light stabilisers in PVC products like patio furniture, window and door trim, fencing and pond liners. Ciba has compared the performance of NOR HALS in PVC favourably with benzophenone and cyanoacrylate stabilisers, as well as with a benzotriazole and a conventional HALS. 

Designs deliberately incorporating flexible rubbery inserts between two stiff adherends are well known. For example, cyanoacrylate adhesives are successfully used to bond spectacle lenses to frames through an intermediate rubber layer. Without the rubber to dissipate peel and cleavage loads, the joint between the lens and the metal frame would be readily over-stressed, resulting in premature failure. 

Both rigid and flexible PVC may be bonded with toughened acrylics, cyanoacrylates and the solvent-based adhesives. However, although not as convenient as the cyanoacrylates, the toughened acrylics give the best overall performance particularly in severe environments. 

Cyanoacrylate adhesives will bond most substrates to themselves and to each other. The few adherends which do not bond well with standard adhesives are polyethylene, polypropylene, EPDM rubber, plasticized PVC, teflon, and acidic surfaces. A few manufacturers sell modified adhesives which will bond some of these materials, such as EPDM and flexible PVC. Adhesion to low surface energy plastics like polyolefins and Teflon can be improved by an etching or oxidizing treatment. 

Cyanoacrylates have wide appeal as industrial product assembly adhesives because they rapidly form strong bonds on so many dissimilar materials. They are particularly useful in joining rigid, impervious substrates which will not be subjected to high heat, high impact, outdoor use, or long-term moisture exposure. They are also useful for bonding flexible adherends to... 

Recent introductions in cyanoacrylate technology include a modified ethyl monomer with considerably improved flexibility over the standard product. These cyanoacrylates were developed for the loudspeaker industry where a degree of flexibility in the bonded joint is desirable. 

Rigid polyvinyl chloride can be easily bonded with epoxies, urethanes, cyanoacrylates, and thermosetting acrylics. Flexible polyvinyl chloride parts present a problem because of... 

Flexible linear macromolecules make up, as mentioned before, the newest class of molecules and are the molecules most important to man. Their number is practically unlimited. For examples, almost all textile fibers are flexible macromolecules, from cotton, silk, wool, hair, and rayon to nylon, polyesters, and aramid. Many structural materials are also flexible macromolecules, such as lumber, compmsites, polyoxyethylene, poly(vinyl chloride), and nylon. Because of the ease of melting, many flexible macromolecules have earned the name plastics, such as polyethylene, polypropylene, polytetra-fluoroethylene, and polyoxides. Many adhesives such as glues, epoxides, poly-(vinyl alcohol), cyanoacrylic polyesters, and ethylene-vinyl alcohol copolymers are based on flexible macromolecules. The unique combination of viscosity and elasticity in the liquid state makes many flexible macromolecules useful as elastomers, of which natural and synthetic robbers and segmented polyurethanes are best known. Class 2 also includes the biolo cal macromolecules carbohydrates, proteins, and DNA. The biological macromolecules alone are practically unlimited in number, as documented by the variety of forms of life. 

Manufecturers Comments Flexible filled cyanoacrylate. High viscosity. Slow cure. Meets the requirements of (USA) MIL-A-46050B. 

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