White Paper Brief: Nylon and Moisture Absorption
NYCOA TOPICS IN ENGINEERED PLASTICS: MOISTURE ABSORPTION AND NYLON
Nylon materials used in many industries, such as sporting equipment and sports accessories, must sometimes function through wild fluctuations in ambient temperature and moisture.
Nylon is often analyzed in both its “conditioned” and “dry” or “dry as molded” forms, but why? This practice touches on one of the most fundamental ways that polymers are analyzed for different applications - moisture absorption.
All Nylon is hygroscopic, meaning that it can absorb and hold onto water. Because it has oxygen atoms incorporated into its structure, Nylon has a high affinity for hydrogen bonds, which is why it attracts water from its environment. Nylon molecules are polar, and as the Nylon’s oxygen bonds well with the hydrogen in water, so too does the oxygen in water bond to hydrogens in Nylon, as it actively draws atmospheric water out of the air.
Nylon will also absorb water more quickly when submerged. Once it has become saturated with water, it will show different performance characteristics, and will display a physical change. Like a sponge, once it’s absorbed water to what it can hold, it will stop. Also like a sponge, you can always dry Nylon to extract the moisture back out, and return the nylon polymer to its “dry” state and performance characteristics. This process can be repeated without damaging the nylon itself.
When Nylon absorbs water it “plasticises”. Plasticizing occurs when the water molecules bond to the chains of nylon molecules and make them more likely to slide among each other at the molecular level. When plasticization occurs in this way, the strength of nylon parts decreases, nylon that is being molded may smoke or emit water in response to the heat and pressure of molding, and already-molded parts will change in size and flexibility.
Some primary effects of plasticization:
Increased impact resistance
Increased flexibility
Increased toughness
Increased part size
Decreased strength
Decreased stiffness
Decreased glass transition temperature
What can be done to prevent the events of moisture on Nylon? Drying the Nylon is always an option, and can take as few as 2-3 hours (or as long as a full day for some grades of nylon and when moisture is very deeply incorporated). Reinforcing parts with fillers can reduce this effect, but even highly filled parts can change by .01%. And an unfilled Nylon 6 part can change in size by .05% at room temperature. Temperature increases will also allow more water to be absorbed into the part. Yield stress and modulus of elongation also increases.
However it’s not all bad news. Nylon parts increase in flexibility, elongation and impact strength when they have absorbed water. For this reason some manufacturers will ship Nylon parts in water, to increase their impact resistance during transit and to allow them to flex or bend when installing them once they’ve arrived. And once the Nylon dries it will regain its normal properties.
While all Nylons are hygroscopic the difference in absorption between grades of Nylon is substantial. In one test Nylon 6 saturated at 9.4% while Nylon 12 saturated at 1.4%. This is especially important when your parts will be working in high humidity environments and their strength is critical. Knowing which properties of your parts are the most important, will help you find the right Nylon grade for your material needs.
NYCOA has spent decades working with Nylon-6 based chemistries, but we have developed into so much more; we offer low-moisture absorption engineered Nylon materials such as our NXTamid long-chain polyamide, Nylon 6.10 and 6.12, and even grades of Super-Tough nylon with especially low moisture absorption.
About NYCOA
NYCOA (the Nylon Corporation of America) commercially manufactures many grades of nylon, including NXTamid, a unique long-chain polyamide with low moisture update and effective as an alternative to nylon 11 and nylon 12. NYCOA has also developed the custom flexible PEBA NY-FLEX, which has shown excellent processability and cold temperature impact strength in rotational molding applications.
All NYCOA products are made in the USA, manufactured in our ISO certified plant located in Manchester, NH. NYCOA is dedicated to plastics engineering, plastics innovation, and a consistent quality earned through operational excellence. NYCOA is dedicated to its customers, and produces specialty engineered polymers for industries and partners around the world, and has plastics compounding capabilities to produce a variety of reinforced and modified grades.
NYCOA manufactures specialty engineered polyamide (nylon) plastics for many industries and applications, including fasteners, hook and loop, extruded parts, injection molding, foamed components, monofilament, powders, and wire and cable jacketing.
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