This is why nylon drools and flashes if it is injection molded wet. Moisture absorbed onto the surface of the nylon resin or part can generally be removed by drying for 3 or 4 hours. However, for moisture that has absorbed more deeply, a much longer drying time is needed, sometimes up to 24 hours or more.
How does nylon absorb moisture?
Nylons absorb moisture in equilibrium with the relative humidity of their immediate surroundings. Figure 1 compares the equilibrium moisture content for several grades of nylon. Intech Power-Core™ PA12GC (Gravity Cast), when fully submerged in water, absorbs a maximum of 1.4% while nylon 6 has an absoption rate of over 10%.
How long does it take for nylon to dry?
Under normal conditions, say 20-80% RH, nylon will reach saturation in about 24 hours. This means that the same amount of drying time will be required to dry material that has sat open for 24 hours or 24 years.
What happens if nylon is wet after melting?
If nylon is molded too wet it will drool, flash, or foam as the bonded water molecules are released when the nylon is melted as all the hydrogen bonding is broken. Moisture absorbed onto the surface can generally be removed by drying for 3-4 hours.
What is the shelf life of nylon?
Nylon does not have a shelf life; there is not a “point of no return” in which the material cannot be dried. Under normal conditions, say 20-80% RH, nylon will reach saturation in about 24 hours. This means that the same amount of drying time will be required to dry material that has sat open for 24 hours or 24 years.
How does nylon absorb moisture?
Nylon is hygroscopic, meaning that it absorbs moisture right out of the air surrounding the material or directly from water if it is submersed. The higher the humidity, the faster it will absorb moisture. Immersing nylon in water will cause it to absorb moisture extremely fast. However, it only absorbs moisture until it is saturated. At that point no amount of humidity will make it absorb more. Similar to a sponge, once the sponge has been soaked in water to saturation, it will not hold more water. Also like a sponge, when nylon is exposed to dryer air, it will give that moisture up and dry out. Nylon does not have a shelf life; there is not a “point of no return” in which the material cannot be dried.
How long does nylon last?
Under normal conditions, say 20-80% RH, nylon will reach saturation in about 24 hours. This means that the same amount of drying time will be required to dry material that has sat open for 24 hours or 24 years.
What happens when nylon is run wet?
Trouble Shooting Defective Nylon Parts. Once the material has been run wet, the moisture has burned away. It will come out of the barrel as steam. The part molded from wet nylon will be dry; therefore you cannot check the moisture content of the part to determine if it was run from wet material.
What is the moisture content of nylon?
The moisture content cannot be controlled well enough to insure anything resembling accuracy. Most nylon manufacturers will recommend drying nylon to below 0.2% moisture content.
Why do you put nylon in water?
Many processors will pack nylon parts in water to improve the impact strength or flexibility. Nylon parts are dry coming out of the molding machine so adding moisture will change the properties. There is confusion about how this works. The property changes that are caused by the moisture absorption are not permanent.
How does a nylon 66 affect the physical properties of the part?
First, it will affect the physical properties of the part. The part will get less brittle and more flexible. These properties will change dramatically . Looking at a typical unfilled Nylon 66, here are some properties for Dry as molded specimens and after the specimens have been conditioned at room temperature and 50% relative humidity:
Why is it important to have a hose fitting on a dryer?
It is also very important that all hose fittings on the dryer be secure. A loose fitting can draw in moist air from the shop and ruin the dry material . It should also be noted that moisture in nylon acts as a lubricant which increases the flow of the material. The higher the moisture content, the higher the flow.
How does nylon absorb moisture?
Nylons absorb moisture in equilibrium with the relative humidity of their immediate surroundings. Figure 1 compares the equilibrium moisture content for several grades of nylon. Intech Power-Core™ PA12GC (Gravity Cast), when fully submerged in water, absorbs a maximum of 1.4% while nylon 6 has an absoption rate of over 10%.
How much does nylon 6.6 drop?
In the case of nylon 6, the drop in tensile strength from dry (100 %) to the saturated state is over 80 %. For nylon 6.6, the drop is over 60 %.
How to prevent moisture on nylon?
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.
What happens to nylon when it is saturated?
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 ...
How saturated is nylon 6?
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.
How does plasticization affect nylon?
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.
What is the name of the company that makes nylon?
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.
Why does nylon attract water?
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.
How much does nylon 6 change in size?
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.
How long does it take for nylon to reach saturation point?
PLA will swell up to 40 microns over a 150-hour exposure period, whereas Nylon, which is much more Hygroscopic, can reach it’s saturation point after only 24 hours of exposure.
What type of filament absorbs moisture?
Filaments that absorb moisture are labeled as hygroscopic, and below is a list of the different filament types placed in order from the most hygroscopic to the least.
What happens when you heat up a filament?
Moisture saturated filament will be more brittle on the spool and have less flex. You will hear cracking and popping sounds when the filament is being heated up in the extruder and you may even notice a bit of steam and bubbles at times.
Why does my filament keep coming out of the nozzle?
Not only can Filament swell when exposed to moisture and increase in diameter of 20-40 microns which can upset the print, but moisture saturated filament will cause extrusion delays, and then when extrusion is stopped, the filament will keep coming out of the nozzle. It may also cause the extruder to jam.
Why is filament storage important?
Filament storage instructions should be taken seriously because if the filament you are using has absorbed any moisture, it will be visible in your prints. Moisture creates bubbling at the extrusion nozzle that results in uneven layers and eventually a print surface that resembles a teenagers’ pimple ridden face.
How long can you keep filament in the over?
If you forgot to store your filament and it got exposed to a lot of moisture, don’t fret! It can still be dried and reused without any issues, but you should try and keep it away from moisture as much as possible since sticking the filament spool in the over for 4-8 hours isn’t that fun.
How to store 3D printed filament?
Moisture can, and will affect both filament and 3D printed parts, which is why it’s so important to store the filament properly in either vacuum sealed bags or in sealed airtight containers with silica gel packets.
What happens when water molecules are absorbed into nylon?
When water molecules become absorbed into the nylon matrix, they attach themselves to the amide groups in the nylon chains. This forces the nylon chains farther apart, reducing the attractive forces between the chains and lowering a property known as the glass transition temperature.
How much water does nylon 6/6 hold?
It will be higher in extremely hot, humid environments or in situations where the part is immersed in water or used in close proximity to water, but in most cases a part molded in unfilled nylon 6/6 can only hold about 1.5% water by weight.
Why is nylon 6/6 so brittle?
Parts produced in an unfilled nylon 6/6 were received from the molder that appeared to be more brittle than usual. The explanation was that the parts had been molded just a few days earlier. It was winter in a northern state where the indoor humidity was very low and therefore moisture uptake was slow.
What is MFR in nylon?
Analysts who use MFR tests to evaluate nylons run into some significant problems. While MFR is used as an indicator of relative average molecular weight in many materials like polycarbonate and polypropylene, few nylon suppliers list MFR values for their materials.
How to moisture condition a polybag?
The moisture conditioning process takes many forms. Some simply pour a prescribed amount of water into molded parts contained in a moisture-proof package such as a polybag. Others prefer placing saturated paper towels into the package with the nylon parts and allowing the water to migrate out of the paper and into the nylon. Some go as far as boiling the parts. This not only increases the moisture uptake rate, but also ensures that the moisture is absorbed more uniformly throughout the wall of the part.
How is the molecular weight of nylon measured?
Therefore, in many cases the average molecular weight of nylon is measured using a property known as relative viscosity. This removes the need to control and measure moisture content because the sample is tested at room temperature where no breakdown of the polymer can occur due to the presence of water.
Why do nonpolar polymers absorb water?
Nonpolar polymers such as polyethylene and polypropylene absorb only about .01% of their weight in water because the polar water molecule has no affinity for these polymers. These materials have a chemistry that resembles a hydrocarbon oil or gasoline and it is well known that oil and gasoline do not mix with water.
How much moisture does nylon 6 hold?
Put another way, PPA generally will not absorb more than 1.5% of its weight in moisture, while nylon 6 can hold up to 7% . Yet PPA resins are still considered hygroscopic and require proper drying prior to processing. It is important to emphasize that there is more at stake here than simply getting unwanted moisture out.
Why is it important to keep moisture levels constant in resin?
Once a resin has been adequately dried, it is important to maintain relatively constant moisture levels throughout the molding run to ensure process and part uniformity. Melt viscosity is influenced by the amount of moisture in resin. More moisture equates with a lower melt viscosity (see Fig. 2).
How to dry hygroscopic resin?
The first step toward optimal drying of hygroscopic resins is to prevent moisture absorption in the first place. Amodel PPA, for example, is shipped with less than 0.15% moisture in vacuum- sealed, aluminum-lined containers that prevent moisture ingress. Once opened, it is critical to reseal packaging containers as quickly and as tightly as possible. Many suppliers provide tools to help molders gauge how long they should dry a resin based on how long its container has been open.
What is the difference between nylon 6 and PPA?
Put another way, PPA generally will not absorb more than 1.5% of its weight in moisture, while nylon 6 can hold up to 7%. Yet PPA resins are still considered hygroscopic and require proper drying prior to processing.
What is a gravity moisture analyzer?
These devices comprise a sensitive weigh scale embedded within a benchtop drying oven to measure how much weight the resin loses during drying.
What happens if you use 0.15% moisture?
Moisture levels upwards of 0.15% can cause cosmetic problems such as splay or silver streaking on the surface of a molded part. Higher levels can lead to hydrolysis, and result in a significant reduction in mechanical properties. This is clearly an issue for any molder. But it underscores the importance of proper drying techniques when specifying specialty resins like PPA, which are often selected for the most demanding applications.
Why is it important to dry PPA?
Proper drying of PPA is critical to maintain mechanical and aesthetic performance in demanding applications , such as this automotive exhaust-gas recirculation valve.
What is the moisture content of nylon?
At room temperature in a “normal” environment where the relative humidity is in the range of 35-65%, the equilibrium moisture content for an unfilled nylon will hover around 1.5-2% by weight. If continually immersed this can increase to 5-8%.
What is the dimensional growth that occurs when parts molded in nylon absorb moisture from the atmosphere?
Many polymers are hygroscopic; they absorb water. Since water vapor is always present in the atmosphere, this is the usual source of the water that becomes absorbed into the polymer.
What percentage of water does acetal absorb?
At room temperature and 50% relative humidity an unfilled acetal will absorb only about 0.2% moisture and will expand by approximately 0.2%, effects that are much less problematic than those encountered in nylon. But acetal is a polar polymer and is capable of taking on larger amounts of water under the right conditions.
How much moisture can polyetherimide absorb?
Materials such as polyethersulfone and polyetherimide can absorb as much as 2% by weight over time. However, because these polymers are amorphous and have extremely high glass-transition temperatures, the effect of this moisture absorption on dimensions and properties is much smaller than it is in nylon.
How does moisture absorption affect polymer expansion?
When the water molecule becomes positioned in this way, it forces the spacing between the polymer chains to increase. The greater the amount of moisture absorption the greater the volumetric expansion. Someone measuring parts will view this as an increase in the size of the part. Typically the increase in size can equal 0.5-0.6% in an unfilled nylon 6 or nylon 6/6 if the exposure occurs at room temperature. If the temperature increases, the moisture absorption levels will increase and the corresponding dimensional changes will become larger. Fillers and reinforcements will reduce this dimensional change, however even a highly filled nylon molded under optimal conditions will still expand by approximately 0.1% or 0.001 in. for every inch of part dimension. This makes it important that the processor and the end user define the conditions under which parts are to be measured for first-article approval.
What is the water bonding in nylon?
For workhorse polymers nylon 6 and nylon 6/6, this takes the glass transition from 65-70 C down to about 10 C. Water has the same hydrogen bonding as nylon; when water enters a nylon part it has the same opportunity to become loosely attached to the nylon chain as does another nylon chain.
Is acetal a nylon?
Acetal is often considered as an alternative to nylon that avoids the difficulties associated with moisture absorption. The fact that acetal is rarely dried prior to processing reinforces this notion that moisture uptake is not a concern. At room temperature and 50% relative humidity an unfilled acetal will absorb only about 0.2% moisture and will expand by approximately 0.2%, effects that are much less problematic than those encountered in nylon.
