Other Curing Characteristics

Cure characteristics of one-component systems categorise adhesives as moisture curable, UV curable, powder blocked isocyanates, etc., and for two-components systems as either polyol-isocyanate reactive curable or polyol-amine reactive curable. 

The curing principle for moisture-curing CASE poljmrethane is described by the reaction of isocyanate groups with water. Polyisocyanate/polyol combinations 

Some of the advantages of moisture curable CASE polyurethanes are that there are no solvent emissions, and an improvement in properties due to the formation of urea groups. 

Silane polyurethane hybrids are urethane-based polymers which have been end-capped with reactive silane groups. Urethane-based and silicone-based sealants are two major, single component sealant technologies useful in many applications. For instance, they are used for sealing and bonding cement-containing compounds, metals, plastics, and glass. 

Urethane-based sealants improve rheological and mechanical properties, and adhere well to a variety of substrates as do silicone-based sealants. However, urethane-based sealants tend not to accumulate dirt and dust and are easier to compound than silicone-based sealants. For this reason, hybrid sealants based on moisture-curable hydrolysable urethane prepolymers have been proposed [43]. Silane polyurethane hybrid sealants are systems that maximise the beneficial features of each of the urethane-based and silicone-based technologies, whilst minimising the undesirable characteristics. 

---

Cure characteristics are shown in Figure 14.15 the antireversion agent has no effect on scorch resistance and time to optimum cure. The beneficial effect becomes apparent when reversion occurs, as observed in the control compound. The compound containing the antireversion agent on the other hand maintains a torque level close to the maximum. 

The primary and secondary amines are discussed in this section. The secondary amines are derived from the reaction product of primary amines and epoxies. They have rates of reactivity and crosslinking characteristics that are different from those of primary amines. The secondary amines are generally more reactive toward the epoxy group than are the primary amines, because they are stronger bases. They do not always react first, however, due to steric hindrance. If they do react, they form tertiary amines. Tertiary amines are primarily used as catalysts for homopolymerization of epoxy resins and as accelerators with other curing agents. 

The total assembly time, from the applieation of the adhesive to entry into the hot press, ranges from 20 to 40 minutes. For part of that time the glue is exposed and can lose moisture rapidly. The viseosity of the glue and other adhesive characteristics change over time and the bonding strength after curing in the hot press is influenced by sueh factors. Automated layup minimizes open assembly and total assembly times. 

Other laboratory instruments able to measure the curing characteristics, the so-called curemeters, are widely used for the routine control of fully compounded rubbers. 

The maximum exothermic temperature reached, the time required for the reaction to attain peak exothermic temperature, and the time of gelation are important factors to be considered when selecting a resin. Reactivity tests provide a method for determining the behavior, uniformity, and curing characteristics of a resin. The use of a resin for a specific application often depends on the reactivity of the resin. Measurements of reactivity are helpful in the evaluation of accelerator, catalysts, and other materials that must be considered for the correct use of the resin. 

The polymerization of acrylic adhesives via free radicals (chain reaction) allows acrylic adhesives to be dispensed and cured using unique techniques. Other types of adhesive products often cure by condensation polymerization reactions which dictate certain cure characteristics and handling techniques. 

Various other tests may be specified to characterize performance and curing characteristics of concrete mix. 

Other types of adhesive may be used with some of the combinations of the above systems the major points for consideration to be taken into account are the curing characteristics of the product, the rheology and the speed of flow required. Figures 1-5 show some typical production applications. 

DSC is a fast, sensitive, screening technique for the selection of photopolymer constituents and optimisation of formulations. Resins can be tested for degree of cure and curing characteristics time-heat flow curves for each photoinitiator. The relative concentration of the photoinitiator or other active components of a resin can be optimised by preparing photospeed curves, i.e., time-percentage conversion plots for a range of concentrations of photoinitiator. 

This has been reported in many other cases also. " The particle size of the rubber phase showed an increase with increase in the curing temperature and ENR content. Other studies also proved this. The effect of ENR on the curing characteristics becomes more significant in the system with more... 

A water borne, heat reactive, liquid phenolic resole with unique flow and cure characteristics for use in a variety of prepreg/composite, honeycomb and other binder applications. 

---