What is the difference in chemical resistance between nylon and PU?

Comparison of Chemical Resistance between Nylon and PU

Nylon (PA) and polyurethane (PU) differ significantly in their chemical resistance:

Acid and Alkali Resistance:

Nylon: Has short-term resistance to dilute acids and alkalis. However, in highly concentrated acids (such as concentrated hydrochloric acid) or alkalis, or in prolonged contact, it undergoes hydrolysis, leading to molecular chain breakage, performance degradation, and swelling and discoloration.

PU: Resistant to weak acids and alkalis (such as acetic acid and ammonia). However, it is extremely unstable to strong acids (concentrated sulfuric acid and nitric acid) and strong alkalis (high-concentration sodium hydroxide), which rapidly destroy its molecular structure, causing dissolution, cracking, and loss of performance.

Organic Solvent Resistance:

Nylon: Has some resistance to alcohols and esters (such as ethanol and ethyl acetate). However, highly polar solvents (phenol and formic acid) disrupt intermolecular hydrogen bonds, causing swelling or even dissolution.

PU: Generally, its solvent resistance is poor. Common solvents such as aromatic hydrocarbons (toluene, xylene) and ketones (acetone, butanone) easily cause them to swell, increase in volume, soften, and significantly degrade their mechanical properties.

Salt Solution Resistance:

Nylon: It exhibits good resistance to common inorganic salt solutions (such as sodium chloride and calcium chloride). However, it may oxidize and electrochemically corrode in high-temperature, highly concentrated salt solutions containing dissolved oxygen.

PU: It is relatively stable in salt solutions of normal concentrations. However, the presence of corrosive impurities (such as iron and copper ions) may catalyze oxidation reactions, accelerating material aging and damage.

To summarize the core differences: Nylon is relatively more stable to dilute acids and bases and some solvents, but is easily dissolved and hydrolyzed by highly polar solvents. PU has reasonable resistance to weak acids and bases, but is very weak to strong acids and bases and most organic solvents, and is prone to swelling and degradation. Both perform well in conventional salt solutions, but special conditions and the influence of impurities should be taken into consideration.