PX521 · flame-retardant grade
PX521-FR
Properties of the FR condition, compared with the other PX521 grades.
Specify for transport interiors, building panels and enclosures needing low flame spread/smoke from an acrylic casting.
What is PX521-FR?
PX521-FR is PX521 in the FR grade — specify for transport interiors, building panels and enclosures needing low flame spread/smoke from an acrylic casting. PX521-FR has a tensile strength of 34 MPa (4.93 ksi), weaker than 59% of polymer grades. Elongation at break is 0.6% and the elastic modulus is 3.2 GPa (0.464 Msi). PX521-FR has a density of 1.78 g/cm³ (0.0643 lb/in³), heavier than 94% of polymer grades. Its glass-transition temperature is 110°C (230 °F). UV Resistant is the default condition FabDigit quotes; FR is available on request or by drawing note.
Advantages
- Polishes to a fine finish — 95/100, better than 98% of polymer grades
- Good UV / weathering resistance — 92/100, better than 93% of polymer grades
- Stiff — 3.2 GPa (0.464 Msi), better than 76% of polymer grades
Limitations
- Limited ductility — 0.6%, worse than 99% of polymer grades
- Heavy — 1.78 g/cm³ (0.0643 lb/in³), worse than 94% of polymer grades
- Low fracture toughness — 1.1 MPa·√m (1 ksi·√in), worse than 80% of polymer grades
- Needs corrosion protection — 70/100, worse than 80% of polymer grades
PX521-FR properties
Typical room-temperature values for PX521-FR — 9 properties are specific to this condition; the rest are grade-level values shared by every PX521 grade. Each bar shows where the value sits among the polymer grades in FabDigit's library — further right is higher.
Physical6
PX521-FR has a density of 1.78 g/cm³ (0.0643 lb/in³), heavier than 94% of polymer grades. Its glass-transition temperature is 110°C (230 °F).
Mechanical15
PX521-FR has a tensile strength of 34 MPa (4.93 ksi), weaker than 59% of polymer grades. Elongation at break is 0.6% and the elastic modulus is 3.2 GPa (0.464 Msi).
Thermal11
PX521-FR is rated for continuous service to 95°C (203 °F). It conducts heat at 0.19 W/m·K (0.11 BTU/hr·ft·°F), worse than 69% of polymer grades. Thermal expansion is 70 µm/m·K (38.9 µin/in·°F).
Electrical7
PX521-FR is an electrical insulator with a dielectric strength of 30 kV/mm (762 V/mil) and a resistivity of 1×10¹³ Ω·m.
Chemical & Environmental3
Corrosion resistance is very good (70/100), worse than 80% of polymer grades. UV resistance is excellent.
Sustainability4
Producing a kilogram of PX521-FR takes about 100 MJ of energy and emits 6.5 kg of CO₂ — less than 61% of polymer grades. Typical recycled content is 5%.
Manufacturability4
PX521-FR's machinability is good (65/100, better than 66% of polymer grades); weldability poor (30/100); formability good (60/100).
Values are nominal handbook figures for design screening. Certified mill or lot data ships with every FabDigit order on request.
Other PX521 grades and fills
PX521 is also supplied in 6 other conditions. The full side-by-side table is on the PX521 overview.
- UV ResistantDefaultDefault choice for outdoor signage, glazing, lenses and displays needing long-term non-yellowing clarity.72 MPa tensile
- OPTPick for lenses, light guides and precision optics where haze and internal stress must be minimal.74 MPa tensile
- EMBPick for thick-section embedments (specimens, trophies, decorative inclusions) where cure exotherm and shrink cracking must be controlled.62 MPa tensile
- IMUse where edge chipping, drilling near edges or vandal/impact loads would crack standard cast acrylic.52 MPa tensile
- MFChoose for cast worktops, sinks and sanitary ware where thickness, stiffness, thermal stability and repairable matte surfaces matter more than clarity.40 MPa tensile
- FRSpecify for transport interiors, building panels and enclosures needing low flame spread/smoke from an acrylic casting.34 MPa tensile
Working with PX521-FR
Is PX521 easy to machine?
Machines cleanly with sharp carbide, high speed/low feed, 0° to slightly positive rake and air or mist cooling; anneal 2–4 h at 75–80 °C before and after heavy cuts to avoid crazing, and avoid coolant with alcohols.
Can PX521 be welded?
Not thermally welded in practice — join with MMA/solvent cement (acrylic dichloromethane or two-part methacrylate adhesive) for optically clear, near-parent-strength bonds; UV-cure acrylic adhesives for clear glazing joints.
Can PX521 be formed, bent or molded?
Cast between silicone/glass tooling at 40–70 °C with post-cure to 90–110 °C; thick sections need slow ramped cure to control exotherm and shrink voids, and finished plate thermoforms at 150–170 °C.
What surface finishes work on PX521?
Sand progressively then flame-, diamond- or buff-polish to optical clarity; accepts hard-coat/anti-scratch and anti-reflective coatings, screen printing and acrylic-compatible paints — mask edges from solvent-based cleaners.
PX521 chemical composition (wt %)
Limits by weight percent from the governing specification, written the way the spec states them — a single maximum for impurities, a range for alloying elements, and the base element as balance. Nominal is the typical mid-range value.
| Element | Spec limit (wt %) | Nominal |
|---|---|---|
| crosslinker (glycol dimethacrylate type)raises solvent and heat resistance of the casting | 0 – 2 | 0.5 |
| peroxide initiator (e.g. dibenzoyl/peroxcure package; sometimes with amine/redox accelerator | 0.05 – 0.6 | 0.25 |
| UV absorber / HALS stabilizerbenzotriazole-type; source of the UV-Resistant designation | 0.1 – 1 | 0.4 |
| release / flow / defoaming additives | 0 – 0.5 | 0.15 |
| alumina trihydrate (ATH) filleronly in MF / FR solid-surface variants (typ. 55–62 wt %) | 0 – 65 | 0 |
| methyl methacrylate (MMA) monomer + PMMAbulk-polymerized in mould; residual monomer typically <1 % after full cure | ≥ 92 (balance) | — |
PX521-FR — frequently asked
What is PX521-FR used for?
PX521-FR is typically used for vacuum casting prototypes, clear industrial prototypes, lenses, light pipes and lighting covers, display and instrument windows, outdoor signage and glazing panels and flow-visualisation and fluid-path models. In short: UV-stable outdoor resin.
What is the tensile strength of PX521-FR?
PX521-FR has a typical tensile strength of 34 MPa (4.93 ksi) — weaker than 59% of polymer grades. Strength varies by condition: see the 7 listed tempers.
Is PX521-FR easy to machine?
Reasonably — machinability is rated good (65/100, better than 66% of polymer grades). Machines cleanly with sharp carbide, high speed/low feed, 0° to slightly positive rake and air or mist cooling; anneal 2–4 h at 75–80 °C before and after heavy cuts to avoid crazing, and avoid coolant with alcohols.
Can PX521-FR be welded?
Not readily — weldability is rated poor (30/100). Not thermally welded in practice — join with MMA/solvent cement (acrylic dichloromethane or two-part methacrylate adhesive) for optically clear, near-parent-strength bonds; UV-cure acrylic adhesives for clear glazing joints.
What surface finishes work on PX521-FR?
Sand progressively then flame-, diamond- or buff-polish to optical clarity; accepts hard-coat/anti-scratch and anti-reflective coatings, screen printing and acrylic-compatible paints — mask edges from solvent-based cleaners.
Can PX521-FR be formed, bent or molded?
Cast between silicone/glass tooling at 40–70 °C with post-cure to 90–110 °C; thick sections need slow ramped cure to control exotherm and shrink voids, and finished plate thermoforms at 150–170 °C.
What is the maximum service temperature of PX521-FR?
PX521-FR is rated for continuous use to about 95°C (203 °F), and briefly to 95°C. Strength falls off well before that limit — check the elevated-temperature data for load-bearing parts.
Can FabDigit make parts in PX521-FR?
Yes — PX521-FR is available for injection molding and 3D printing with instant online pricing. Upload a STEP file to get a price and a DFM check.
Sources
- Engineered Materials Handbook Vol. 2: Engineering Plastics (PMMA section) — ASM International (1988)
- CAMPUS plastics database — PMMA cast/moulding grades typical values — CWFG / CAMPUS consortium (2024)
- ISO 7823-1 Cast poly(methyl methacrylate) sheets — requirements and test methods — ISO (2003)
- ASTM D4802 Poly(methyl methacrylate) Acrylic Plastic Sheet — ASTM International (2021)
- Cast acrylic sheet & casting-resin technical data (clear, impact-modified, mineral-filled solid surface) — Acrylic sheet/resin producers (2023)
Property data is compiled from published supplier and standards handbooks and normalised for comparison. Nothing on this page is a certification — request mill certs, CoC or material test reports with your order.