Painted Nylon and Moisture Absorption

One of the articles on this website that garners the most attention is Understanding Nylon and Moisture. Recently, a reader posted an interesting question that I had not thought of. The reader asked if painting a nylon part would stop the nylon from absorbing moisture and thus prevent the change in properties inherent in the moisture absorption process.

I had never thought of this before and a google search revealed no answers to this question. I have a large amount of nylon processing and technical information from DuPont and this subject is not discussed.

So, I set about running my own experiment.

I thought that the best way to test this would be to perform tensile strength testing on test bars molded from Nylon. The tensile strength of nylon drops significantly as the material absorbs moisture from the atmosphere. The tensile strength is acting as a stand-in for the moisture content because measuring the moisture content directly in parts is difficult.

I molded test specimens from an unfilled Nylon 6. I placed 3 specimens in a 4 mil plastic resealable bag right after molding. This bag was then put inside another bag. Another 3 specimens were not sealed up after molding, and yet another set of specimens was painted.

I spray painted the specimens with Krylon Fusion spray paint that is made for plastic. The can says that you can use it on any type of plastic. I coated the bars very well right after molding. I got a few runs because I wanted to get a thick coating on them.

I ended up putting the moisture conditioned bars and the painted bars in a container with water in the bottom to speed up the moisture conditioning.

I let the test specimens’ condition for 24 hours and set about testing them for tensile strength. I ran the tensiles on an Instron machine at 2 inches per minute cross-head speed. Here are the results:

Dry as molded specimens – 10,900 psi (75.4 Mpa)

Moisture Conditioned unpainted specimens – 8,660 psi (59.7 Mpa)

Painted and moisture conditioned specimens – 9100 psi (62.8 Mpa)

It does not appear that the paint coating protected the specimens from moisture absorption although it may have slowed down the moisture absorption. The moisture conditioned bars show a 20.6% reduction in tensile strength but the painted bars show a 16.5% reduction.

My theory is that the paint is permeable to moisture and allows some moisture to penetrate the nylon through the paint.

It is also possible that the coating itself is artificially adding tensile strength to the test specimens but it is a pretty thin coating. The paint added 0.0035 inches to the thickness of the test specimens on average. This additional thickness was accounted for in the calculations. If the additional 440 psi of tensile strength was the strength of the paint coating that would mean that the paint tensile strength is 251,000 psi which is unlikely.

Based on this study, I would suggest that the idea of painting nylon in order to keep it from absorbing moisture is plausible. There may be some paints that would be much more impermeable to moisture than what I used. I am not a paint expert by any means. It might also be possible to achieve this by over-molding another material over a nylon part or coating a nylon part with some type of ceramic coating like Ceracote.

The key would be to coat these parts quickly after molding. Nylon absorbs moisture so fast that if you waited for 12 hours to coat the parts, it would be too late. You could however dry the parts and then coat them.

The results of this experiment were not as open and shut as I had hoped but I hope that it gives you a little insight.

Weekly News Digest: November 21, 2022

Resin Price Report: Relative stability expected through end of year

The Plastics Exchange Market Update: November 11, 2022

Resin prices still dropping

Shell begins PE production at new PA plant

CP Chem and QatarEnergy to proceed with PE plant in Orange TX

Evonik working with 2 new distributors in Europe

SABIC launches new PC copolymer aimed at solar panel connectors

Lyten develops new graphene infused LLDPE

Weekly News Digest November 14, 2022

Resin Price Report: Market turns slightly bullish

The Plastics Exchange Market Update: November 4, 2022

PS prices drop in US

Nexeo to distribute Teknor Apex TPE grades

Celanese completes acquisition of DuPont materials business

Hexpol to acquire McCann Plastics

Kraiburg develops new TPE series that is bondable to PC, ABS and PETG for medical applications

Ascend to purchase majority of California carpet recycler Circular Polymers

This Week in History

November 17, 2014: Styrolution becomes wholly owned by INEOS and changes name to INEOS Styrolution

November 18, 1998: Hoechst AG announces that it is spinning off its Hoechst Celanese division. The new company will be called Celanese AG

November 19, 1872: The injection molding machine was patented by John Wesley Hyatt

Weekly News Digest: November 7, 2022

Resin Price Report: October scares up highest trading tally since May

The Plastics Exchange Market Update: October 28, 2022

DuPont pulls out of Rogers Corp acquisition

FDA seeks increase for color additive certification

Avient launches new density modified materials that feel and look more like metal

HIG Capital acquires distribution arm of Avient, will change name to Formerra

LyondellBasell to reduce output in US to match lower demand

Celanese closes acquisition of Dupont’s materials business

Weekly News Digest October 31, 2022

Resin Price Report: Demand improves, supply tightens in spot PP, PE markets

The Plastics Exchange Market Update: October 21, 2022

Borealis introduces new PP catalyst technology

Kraiburg introduces new TPE grades for hiking equipment

Ascend develops new FR materials for EV applications

European polymer demand restrained by worries over economy

K2022 trade show attendance slips 21%

Plastics Technology magazine hosting Extrusion 2022 conference December 6-8 in Charlotte NC

This Week in History

November 1, 1984: The 1985 Chevrolet Cavalier becomes the first vehicle to have front and rear bumper fascia’s made from injection molded TPO. The material wat Himont ETA3041.

November 4, 1986: Hoechst AG of West Germany acquires Celanese Corporation of America to form the world’s largest chemical company which will be called Hoechst Celanese.

Weekly News Digest October 24, 2022

Resin Price Report: Prime PE, PP resin prices slip some more

The Plastics Exchange Market Update: October 14, 2022

E-bike company shows prototype airless tires made from Hytrel

New VW van uses largest ever thermoplastic tailgate

Ascend develops new FR nylon grades for EV applications

EU approves Celanese’s acquisition of DuPont’s materials businesses

Ascend launches new nylon 66 grades for medical applications

This Week in History

October 24, 1911: Nathanial C Wyeth who patented the PET bottle in 1973 was born.

October 25, 2013: Celanese announces that the Ticona company name will be removed from its polymer products, such as Celcon brand acetal, and replaced with the Celanese company name. Ticona was formed in 1963 as a joint venture between Celanese Corporation of America and Hoechst AG.

October 27, 1938: DuPont officially unveils a new product called “Nylon” to the public.

October 30, 1956: Neal MacDonald Robert at DuPont is granted a patent for acetal homopolymer.

Weekly News Digest: October 17, 2022

Resin Price Report: Downward pricing pressure still a factor

The Plastics Exchange Market Update October 7, 2022

Ascend launches a new line of PA66 grades for medical applications

M Holland to distribute LyondellBasell Purell materials for medical applications

Toray to increase carbon fiber capacity at Alabama plant

UBE develops new PC based TPU grades

Teknor Apex develops new FR PVC grades for wire and cable applications

Milliken develops colorant line designed for demanding applications

France’s Benvic now offering TPE’s in addition to PVC compounds

Weekly News Digest-October 10, 2022

Resin Price Report: PP resin prices drop for seventh straight week

The Plastics Exchange Market Update 9/30/2022

Aurora Plastics and Enviroplas to merge

The 1987 VW Golf sported the first molded on color weatherable grill

Ampacet invests in clean rooms for production of medical grade masterbatches

Kraiburg introduces new TPE series for cosmetics packaging

Asahi unveils new PPE grades for 5g applications

Trinseo mulling closure of its styrene monomer plant in Bohlen Germany

Weekly Resin Report October 3, 2022

Resin Price Report: Ian batters Florida but spares petrochemical industry

The Plastics Exchange Market Update: 9/23/22

Solvay to increase PPA capacity at Augusta Georgia plant

Arkema to increase capacity for its Pebax PEBA TPEs at Serquigny, France plant

SABIC to introduce several new materials for railway components at InnoTrans trade show

Lanxess develops new PBT grades for electronics applications

Alphagary launches new PVC compounds with recycled content

HammerTek develops new elbows for silo piping that reduce wear

ExxonMobil expands line of polyolefins for medical applications

Tolsa launching new FR masterbatch line

Conventus Polymers to distribute SABIC high performance product line

We can look forward to visits from sustainability auditors

Weekly News Digest August 26, 2022

Resin Price Report: Producer efforts to reduce PE output start to bear fruit

The Plastics Exchange Market Update September 16, 2022

DSM completes expansion of Evansville IN plant

BMW and Mini sub-brand to get vegan interiors (I suggested this years ago)

Sinochem/Elix open new compounding plant in China

LyondellBasell licenses its high pressure PE technology to Hanwha

RadiciGroup acquires engineering materials business of the Indian company Ester Industries Ltd

Avient develops new laser weldable PC grades

SABIC develops new PEI grades that are near infrared transparent

Dow looking to increase PE prices

Pemex PE plant in Mexico is down after pipeline explosion

Ukraine boondoggle puts EU circular economy goals at risk

FRX develops new FR additives for PC and PC alloys

SABIC develops new extrusion grade PC copolymers for passenger train interior parts