PC Sheet Chemical Compatibility: Adhesives, Seals and Cleaners That Destroy It
The short version
A polycarbonate (PC) machine guard or vision panel that “was fine at installation, then grew hairline cracks around the bolt holes months later” is almost never a strength problem. It is usually environmental stress cracking (ESC): the sheet carries internal stress from machining and assembly, it comes into contact with an incompatible chemical, and the combination initiates micro-cracks exactly where stress concentrates.
Two main lines from Section 3.6 of the Exolon® manual will keep you out of trouble:
- Compatibility is not a simple yes/no. The actual outcome depends on four factors: concentration, temperature, duration of contact, and the internal stress level of the sheet.
- PC’s boundaries are clearly drawn. It resists mineral acids, salt solutions and most oils and waxes — but alkalis, ammonia and amines, aromatic/halogenated solvents, aldehydes, ketones, esters and methanol are off-limits.
1. Why contact can crack the sheet: three damage modes
The manual groups chemical attack on PC into three types, which can occur singly or together:
| Damage mode | Mechanism | Visible result |
|---|---|---|
| Dissolving / swelling | Low-molecular, aromatic or halogenated and polar components migrate into the plastic | From a sticky surface to complete dissolving |
| Stress cracking | Chemicals migrate into the surface, locally relaxing internal stress and producing microscopic cracks | Micro-cracks act as notches; mechanical properties drop |
| Molecular reduction | A chemical reaction shortens the polymer chains | Impact resistance and elasticity suffer; electrical properties are rarely affected |
Stress cracking is the stealthy one: the chemical only has to migrate into the surface — it does not need to corrode the sheet away. And internal stress comes mainly from processing and assembly — drilling, milling, bending, tightening — precisely the areas where adhesives and gaskets sit for years. That is why cracks start at hole edges, bend zones and clamping lines.
2. The compatibility boundaries from the manual
Section 3.6 of the Exolon® manual, condensed into two tables:
PC resists:
| Class | Manual wording |
|---|---|
| Mineral acids | Resistant up to the highest concentrations |
| Salt solutions | Neutral and acidic |
| Oxidising and reducing agents | Resistant |
| Saturated, aliphatic hydrocarbons and alcohols | With one exception: methanol |
| Oils, fats and waxes | Many are tolerated |
PC is damaged by:
| Class | Common engineering examples (representatives of the class, not individually listed in the manual) |
|---|---|
| Alkalis | Strongly alkaline cleaners, etc. |
| Ammonia and amines, incl. their solutions | Amine-containing cleaning products, some curing-agent components |
| Aromatic / halogenated solvents | Toluene, xylene, trichloroethylene, etc. |
| Aldehydes, ketones and esters | Acetone, ethyl acetate, etc. |
| Methanol | Named separately as the alcohol exception |
For substance-by-substance data the manual refers readers to request more detail — which is itself a warning: “compatible as a class” does not mean “every brand is compatible”.
3. Three assembly pitfalls (engineering practice)
On the shop floor, the class list above turns into three items. The recommendations below reflect engineering practice; verify on critical parts under real conditions:
- Be careful with threadlockers. Methacrylate-based threadlockers (Loctite 243 and similar) pose an ESC risk in contact with PC. Do not apply them onto the sheet or into its holes; prefer mechanical locking, and keep threadlocker on the metal parts only.
- Avoid PVC gaskets. Plasticizers from PVC gaskets migrate into the PC surface and are a classic ESC trigger. EPDM or neutral silicone rubber gaskets are the safer choice.
- Choose neutral-cure silicone adhesives. Neutral RTV silicone (e.g. 706-type) behaves well with PC in practice. Solvent-bearing super glues and contact cements, and unverified epoxies or polyurethanes, should be sample-tested first.
On the machining side, Section 4.1 of the manual is explicit: cutting oils and oil-based emulsions are forbidden — their additives can cause stress crack formation. Cool with water or oil-free compressed air only. The same logic applies to cleaners: solvent-based, amine-containing and strongly alkaline products are all off-limits — see our PC sheet cleaning guide.
4. Quick do / don’t table
| Area | Recommended (whitelist) | Use with care / forbidden (blacklist) |
|---|---|---|
| Fastener locking | Mechanical locking; threadlocker never touches the sheet | Methacrylate threadlocker applied directly onto PC |
| Gaskets / seals | EPDM, neutral silicone rubber | PVC and other plasticized soft plastics |
| Bonding / sealing | Neutral-cure RTV silicone | Solvent-based or acidic adhesives; unverified epoxy/PU |
| Machining coolant | Water, oil-free compressed air | Cutting oils, oil emulsions (explicit in the manual) |
| Cleaning | Water + microfibre cloth, non-abrasive detergent | Solvents, amine products, alkalis, ammonia glass cleaners |
FAQ
Q1: Can ethanol or isopropyl alcohol touch PC at all? Yes, for spot cleaning. The manual allows removing splashes of dye, grease or residual sealant with a soft cloth soaked in ethyl alcohol, isopropyl alcohol or petroleum ether (boiling point 65 °C) — prior to curing, with gentle rubbing. It is a spot-treatment guideline, not a licence to soak or scrub the whole sheet. Methanol is always forbidden.
Q2: Why does the sheet crack months after assembly, not immediately? ESC is the long-term combination of stress and chemicals: substances migrate along contact surfaces into high-stress zones (hole edges, bends, clamping lines), microscopic cracks form first — invisible to the eye — and then act as notches that amplify impact and vibration loads. Investigate both questions together: where is the stress, and what has the sheet been in contact with?
Q3: Is there an adhesive that is absolutely safe for PC? No “absolute” exists. Concentration, temperature, contact time and stress level all change the outcome. Neutral silicone and EPDM perform well in practice, but for critical structural parts, run a sample test under real conditions and observe the assembly over time — instead of trusting the words “all-purpose” on the bottle.
Closing
Wuxi Cremage Technology machines PC and acrylic equipment guards and vision windows every day. Compatibility pitfalls — gasket materials, locking schemes, cleaning rules — are part of what we screen for customers during material selection and assembly. If one of your guards has cracked “for no reason”, send us the assembly details and operating environment, and we will help you trace the stress-plus-chemical combination behind it.
Further reading: PC sheet installation, rabbets and gaskets, PC sheet CNC machining parameters (the official basis for banning cutting oils), PC and acrylic deformation control (another source of assembly stress). For product options, see acrylic equipment guards.