Moisture for nylon

Figure 3-74. Izod Impact Strengths vs Moisture for Nylons 6, 6/6, and 6/10 (Ref. 24)...

Use the molecular weight ratio to calculate the apparent extent of reaction of the caprolactam in these systems. Is the variation in p qualitatively consistent with your expectations of the effect of increased water content in the system Plot p versus moisture content and estimate by extrapolation the equilibrium moisture content of nylon-6 at 255 C. Does the apparent equilibrium moisture content of this polymer seem consistent with the value given in Sec. 5.6 for nylon-6,6 at 290°C ... 

The packaging (qv) requirements for shipping and storage of thermoplastic resins depend on the moisture that can be absorbed by the resin and its effect when the material is heated to processing temperatures. Excess moisture may result in undesirable degradation during melt processing and inferior properties. Condensation polymers such as nylons and polyesters need to be specially predried to very low moisture levels (3,4), ie, less than 0.2% for nylon-6,6 and as low as 0.005% for poly(ethylene terephthalate) which hydrolyzes faster. 

The pelargonic acid by-product is already a useful item of commerce, making the overall process a commercial possibiUty. The 13-carbon polyamides appear to have many of the properties of nylon-11, nylon-12, or nylon-12,12 toughness, moisture resistance, dimensional stabiUty, increased resistance to hydrolysis, moderate melt point, and melt processibiUty. Thus, these nylons could be useful in similar markets, eg, automotive parts, coatings, fibers, or films. Properties for nylon-13,13 are = 56 (7 and = 183 (7 (179). 

Compared with nylon 66 fibres, the polyurethane fibres (known as Perlon U) have a tensile strength at the higher end of the range quoted for nylon 66, they are less prone to discolouration in air, are more resistant to acid conditions and they have a lower moisture absorption. On the debit side they are less easy to dye, are hard, wiry and harsh to handle and have too low a softening point for many applications. They are currently of little importance but have found some use in bristles, filler cloths, sieves and a few other miscellaneous applications. 

Typical applications for nylon include small gears, bearings, bushes, sprockets, housings for power tools, terminal blocks and slide rollers. An important design consideration is that nylon absorbs moisture which can affect its properties and dimensional stability. Glass reinforcement reduces this problem and produces an extremely strong, impact resistant material. Another major application of nylon is in fibres which are notoriously strong. The density of nylon is about 1100 kg/m. ... 

Wet winding lubricant for nylon and polyester carpet yarns. Enhances moisture regain after heatsetting. 

The effect of moisture on nylon 6 resins is well-known and well-documented. (15) Because of this, the susceptibility of nylon block copolymers to moisture absorption was expected. Evaluation of requirements for exterior automotive body panels and other applications requiring dimensional stability indicated that early nylon block copolymer formulations would not meet specifications... 

Figure 2. Crack growth rate V5. stress intensity factor range for nylon 66 (Series B) containing various levels of moisture...

However, it is moisture absorption that gives nylon its toughness. Upon initial injection molding manufactured nylon profiles are typically very hard and brittle. After they left to cure, they absorb moisture from the air and become very impact resistant. The curing (or softening ) period for nylon profiles takes 2-3 weeks. Clearly, at outdoors conditions it usually takes much less time. 

Nearly every polymeric system absorbs some moisture under normal atmospheric conditions from the air. This can be a difficult to detect, very small amount as for polyethylene or a few percent as measured for nylons. The sensitivity for moisture increases if a polymer is used in a composite system i.e. as a polymeric matrix with filler particles or fibres dispersed in it. Hater absorption can occur then into the interfacial regions of filler/fibre and matrix [19]. Certain polymeric systems, like coatings and cable insulation, are for longer or shorter periods immersed in water during application. After water absorption, the dielectric constant of polymers will increase due to the relative high dielectric constant of water (80). The dielectric losses will also increase while the volume resistivity decreases due to absorbed moisture. Thus, the water sensitivity of a polymer is an important product parameter in connection with the polymer s electrical properties. The mechanical properties of polymers are like the electrical properties influenced by absorption of moisture. The water sensitivity of a polymer is therefore in Chapter 7 indicated as one of the key-parameters of a polymeric system. 

A comparison of the commercial moisture-regain values for several fibers is shown in Table 11.5 [58]. In general, cellulose acetate occupies an intermediate position, indicating a good balance. Its value of 6.5% is close to the value of 7.0% for natural cotton yarn. The values of 3.5% for triacetate and 4.5% for nylon indicate that these fibers are not nearly as hydrophobic as acrylics at 1.5% and polyester at 0.4% commercial moisture-regain. 

Uses Urethane for coatings for nylon and polyester fabric Features Water-based provides high hydrostatic resist, and moisture vapor props. 

Chem. Desetip Water-based PU coating Uses Urethane for breathable coatings for nylon and polyester fabrics Features Provides high mullens and moisture vapor transfer props. Properties Tens. str. 1200 psi 100% tens. mod. 400 psi elong. 300% hydrostatic resist. (Mullens) 90-100 psi 40 2% solids Solucote 1073 [SoluoQ... 

Chem. Desaip. PU base coat in toluene/IPA Uses Base coat for nylon and polyester fabrics Features Breathable durable provides high hydrostatic resist., moisture vapor transfer, and tapeability to be used with Solucote Top 920 Properties Vise. 40,000 2000 cps tens. str. 2500 psi 100% tens. mod. 2100 psi elong. 110% hydrostatic resist. (Mullens) 100-200 psi 44 2% solids... 

Let us calculate for nylon 6,6 at 276°C (and low moisture levels) from Ka = 53.78 for nylon 6,12 [38] and Equation 7.39. First, assume that both polymers have the same thermodynamic equilibrium constant Keq and the same ratio of activity coefficients for the functional groups yaYb)Iyz so that, rearranging Equation 7.39 gives ... 

Nylon 6,12 (7 = 209°C) absorbs less moisture than nylon 6,10 because of the strong aliphatic character of the polymer, and this gives the polymer greater rigidity in the wet state. Consequently, as with nylon 12, nylon 6,12 is used for injection-molded parts. 

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