Thermoplastic/thermoset adhesive

Even in cases where one cannot unambiguously identify the components of a complex blend by its individual degradation pattern, it stiU may be possible to use the blend s TGA degradation curve as a quality control tool. For example, a commercial blend of an acrylonitrile-butadiene (ACN/BD) copolymer and a phenolic resin yields a tough thermoplastic/thermoset adhesive when cured that can hold brake linings in place and meet other demanding industrial applications. Isothermal cure of this adhesive was described in Section 3.4.3. 

Figure 3.40. TGA mass loss and derivative DTG curves of a thermoplastic/thermoset adhesive. Sample was predried prior to the first run. Heating rate was 15 °C/min in nitrogen. [From Tabaddor et al. (2000) with kind permission from Springer Science and Business Media.l...

Differential scanning calorimetry (DSC), DMA and TG were used by Tabaddor and co-workersl l to investigate the cure kinetics and the development of mechanical properties of a commercial thermoplastic/ thermoset adhesive, which is part of a reinforced tape system for industrial applications. From the results, the authors concluded that thermal studies indicate that the adhesive was composed of a thermoplastic elastomeric copolymer of acrylonitrile and butadiene phase and a phenolic thermosetting resin phase. From the DSC phase transition studies, they were able to determine the composition of the blend. The kinetics of conversion of the thermosetting can be monitored by TG. Dynamic mechanical analysis measurements and time-temperature superposition can be utilized to... 

Tabaddor PL, Aloisio CJ, Bair HE, Plagianis CH, Taylor CR. Thermal analysis characterization of a commercial thermoplastic/thermoset adhesive. J Therm Anal Calorim 2000 59 559-70. 

An early study by Rudkin (1950) showed that substitution of OH groups with acetyl resulted in a significant decrease in bond strength between the wood and a UF resin in lap-joint tests. Vick and Rowell (1990) studied the adhesive bonding of acetylated yellow poplar, with 18 different thermoplastic and thermosetting adhesives. The effectiveness of the adhesives was examined by determination of bond shear strength (and wood failure) of 6 mm thick, bonded wood strips after conditioning at 27 °C and... 

Thermoplastic Adhesives. The polymer adhesives described in the following sections are not used as extensively with wood as the thermosetting adhesives discussed earlier. However, they do illustrate many interesting principles of the chemistry of adhesion through organic polymers. 

Heat resistant Intractable thermoset polylmides (Vespel, Kinel, Kapton) have been supplemented by injection moldable polyamlde-lmides (Torlon) and modified polylmides (Kanox, Toramid).( Thermoplastic polyimide adhesives were cited as one of the top 100 Inventions in 1981. Polyimide foam does not Ignite at temperatures below 4300C and is being considered as a cushioning material in public conveyances. 

The information is limited to the most important materials, metals, plastics, (thermoplastics, thermoset materials, foams), ceramics, glass and their possible combinations. For papers, cardboards, wood, rubber polymers, usually physically setting systems (solvent-based, dispersion, hot-melt adhesives) are utilized. In these cases, the adhesive selection with regard to the manufacturing conditions and demands is of less problematic nature. 

Thermal stress Regarding the thermal resistance of the bonded joints, thermosetting adhesives are to be preferred to thermoplastically curing adhesives. The following information is useful for the determination of thermal stress ... 

One class of such materials is the fluorinated alkyl esters of acrylic and methacrylic acid, a number of which have been prepared [1]. One of these esters, poly(l,l-dihydropentadecafluoro-octyl methacrylate), has a 11 dynes per cm.—less than Teflon TFE or even FEP [4]. Such materials, and others within the general class of unsaturated, appropriately fluorinated, polyesters warrant investigation for use either as thermoplastic hot-melt adhesives, or for cross linking in situ to form rigid thermoset adhesives. The saturated, appropriately fluorinated polyesters also warrant investigation as thermoplastic hot-melt adhesives. 

Figure 4.21 Relative strengths of thermoplastic and thermosetting adhesives T is the melt temperature of the thermoplastic adhesive Tg is the glass-transition temperature of the thermosetting adhesive).

A polymer is composed of repeating units (i.e., monomers) that are linked together into long chains that can be linear, branched, or cross-linked. If a polymer contains two different types of monomers, it is a copolymer. A linear polymer is a thermoplastic. At elevated temperatures it melts and flows as a liquid. In a cross-linked polymer, the repeat units are actually linked into a three-dimensional network of macroscopic size. It is a thermoset. Once the polymerization is completed, the cross-linked polymer cannot be softened or melted. It is hard, infusible, and insoluble. Hence a thermoset adhesive is the most durable but is also difficult to characterize as compared to a thermoplastic one. 

Part VI is totally new. It is an introduction into polymer technology and thus discusses thermoplasts, thermosets, elastomers, fibers, coatings, and adhesives with respect to their end-use properties. It also contains chapters on additives, blends and composites. 

Uses Coupling agent for mosf thermoset and thermoplastic resins adhesion promoter for solv., water-based, solventless, and powd. coating systems pigment treatment tood-contact coatings Features Esp. effective in PS, polyolefin, epoxy systems Regulatory FDA 21 CFR 175.300, when coupled with silica, as adjunct to epoxy resins in contact with nonacidic, aq. or dry solid foods at temps, below 88 C... 

---