General Purpose
Standard optical grade PMMA for typical applications. Light transmission 92%, good flow, moderate impact.
Acrylic Overview
Poly(methyl methacrylate) (PMMA), commonly known as acrylic or acrylic glass, is a transparent thermoplastic known for exceptional optical clarity, weatherability, and surface hardness. First developed in the 1930s, PMMA has become the material of choice for applications requiring glass-like transparency combined with lighter weight and better impact resistance than mineral glass.
As an acrylic resin distributor, Formerra provides access to multiple acrylic grades including general purpose, high flow, impact-modified, and specialty optical formulations for automotive, lighting, medical, and consumer applications.
PMMA is produced through free radical polymerization of methyl methacrylate monomer. The resulting polymer features excellent light transmission, UV resistance, and surface gloss. The amorphous structure delivers optical clarity without the haze or yellowing common in other transparent polymers.
Acrylic pellets are available in various grades including optical, injection molding, extrusion, medical, and impact-modified formulations.
Optical clarity is the defining property of PMMA. The material transmits up to 92% of visible light, exceeding polycarbonate and approaching the performance of optical glass. Light transmission remains stable over years of outdoor exposure when UV-stabilized grades are selected. This clarity supports applications in automotive lighting, light guides, lenses, and display components.
UV and weatherability resistance is another key strength. PMMA demonstrates minimal yellowing or property degradation after years of outdoor exposure. The material maintains gloss, color stability, and mechanical properties under sunlight far better than polycarbonate or polystyrene. This outdoor durability makes acrylic resin ideal for signage, architectural glazing, automotive tail lights, and exterior trim.
Surface hardness exceeds most thermoplastics. PMMA resists scratching and marring during handling, assembly, and use. The hard surface accepts polishing to restore optical quality after minor damage. This scratch resistance supports applications in automotive instrument clusters, protective covers, and consumer products.
PMMA offers excellent dimensional stability. The material exhibits low moisture absorption (0.2-0.3% at equilibrium) compared to polycarbonate or nylon. Lower water uptake means more predictable dimensions and fewer processing challenges in humid environments.
Colorability and aesthetics distinguish acrylic from other transparent polymers. PMMA accepts transparent, translucent, and opaque colorants while maintaining superior clarity and brilliance. The material delivers vivid colors and special effects including metallics, pearls, and fluorescents.
Processing versatility enables multiple manufacturing methods. Acrylic pellets process through injection molding, extrusion, blow molding, and thermoforming. The material flows well at moderate temperatures and releases cleanly from mold surfaces.
Performance Characteristics
Mechanical Properties
Tensile strength
60-75 MPa (unfilled),
80-110 MPa (glass-filled)
Tensile modulus
2,800-3,300 MPa (unfilled),
5,000-8,000 MPa (glass-filled)
Flexural strength
90-130 MPa (unfilled),
140-200 MPa (glass-filled)
Flexural modulus
2,900-3,400 MPa (unfilled),
5,500-8,500 MPa (glass-filled)
Elongation at break
2-6% (unfilled),
1-3% (glass-filled)
Notched Izod impact
15-25 J/m (unfilled),
100-400 J/m (impact modified)
Hardness
Rockwell M85-105,
Shore D85
Thermal Properties
Continuous use temperature
70-90 °C (unfilled)
Heat deflection temperature
85-105 °C at 0.46 MPa (unfilled),
90-110 °C at 1.8 MPa
Glass transition temperature (Tg)
105-115 °C
Melting point
None (amorphous)
Processing temperature range
200-260 °C
Thermal conductivity
0.17-0.19 W/m·K
Coefficient of linear thermal expansion
70-80 × 10⁻⁶ /°C
Operating Environment
Water absorption
0.2-0.3% in 24 h at 23 °C. Moisture absorption at saturation reaches 0.3-0.4%. The low hygroscopic nature of acrylic resin reduces pre-drying requirements compared to polycarbonate or polyamide. Lower moisture sensitivity delivers more stable dimensions and fewer processing issues in humid environments. Parts maintain dimensional stability across varying humidity conditions.
UV/weatherability rating
Excellent. PMMA demonstrates superior outdoor durability among transparent thermoplastics. UV-stabilized acrylic pellets maintain clarity, gloss, and mechanical properties after years of outdoor exposure. Yellowing and property degradation remain minimal compared to polycarbonate, which requires UV coatings for outdoor applications. This inherent UV resistance makes acrylic resin the preferred choice for automotive exterior lighting, outdoor signage, and architectural glazing.
Hydrolysis resistance
Excellent. PMMA resists hydrolysis across a wide pH range and temperature spectrum. The polymer backbone lacks hydrolyzable groups present in polycarbonate and polyester. Acrylic resin maintains properties in hot water, steam, and humid environments where PC would degrade. This stability supports applications in plumbing fixtures, aquarium components, and outdoor products.
Stress cracking sensitivity
Moderate susceptibility to environmental stress cracking when exposed to certain solvents under load. Alcohols, ketones, aromatics, and chlorinated solvents cause crazing or cracking in stressed parts. Careful material selection and stress relief through annealing reduce ESC risk. PMMA shows better stress crack resistance than polystyrene but inferior performance to polycarbonate under mechanical stress.
Electrical Properties
Dielectric strength
18-20 kV/mm
Dielectric constant
2.6-3.2 at 1 MHz
Dissipation factor
0.04-0.06 at 1 MHz
Volume resistivity
10¹⁴-10¹⁵ Ω·cm
Surface resistivity
10¹⁴-10¹⁵ Ω
Optical Properties
Light transmission
90-92% (visible light, 3 mm thickness)
Refractive index
1.49-1.492
Haze
<1% (clear grades)
Yellowness index
<1.5 (natural, unweathered)
Birefringence
Low (amorphous structure)
Physical Properties
Density
1.17-1.20 g/cm³ (unfilled),
1.25-1.40 g/cm³ (glass-filled)
Melt flow index (MFI)
2-15 g/10 min at 230 °C/3.8 kg (varies by grade)
Mold shrinkage
0.3-0.7% (flow direction)
Water absorption at equilibrium
0.3-0.4%
Flammability rating
UL94 HB (typical),
V-0 available with flame retardants
Chemical Resistance
Excellent resistance
Dilute acids (pH 3-6), dilute bases (pH 8-11), aliphatic hydrocarbons (hexane, heptane), mineral oils, water, salt solutions
Good resistance
Weak alcohols (ethanol at <50%), glycols, household detergents, dilute alkaline cleaners
Limited resistance
Strong acids (concentrated sulfuric, nitric), strong bases (>10% NaOH), oxidizing agents
Poor resistance
Ketones (acetone, MEK), esters (ethyl acetate), chlorinated solvents (methylene chloride), aromatic hydrocarbons (benzene, toluene), strong alcohols (methanol, isopropanol at >50%)
PMMA offers better chemical resistance to dilute acids and bases compared to polycarbonate but shows greater sensitivity to alcohols and solvents.
Strengths, Weaknesses & Operating Limits
Key Strengths
- Optical Clarity: Light transmission of 90-92% exceeds polycarbonate (87-89%) and approaches optical glass performance. PMMA maintains clarity over extended periods without the yellowing common in PC or other transparent polymers. The material delivers consistent optical performance across varying thicknesses and processing conditions. This superior transparency supports demanding applications in automotive lighting, medical optics, and display components where clarity directly impacts performance.
- UV and Weatherability: PMMA demonstrates exceptional outdoor durability without protective coatings. The material resists UV degradation, maintains surface gloss, and shows minimal yellowing after years of outdoor exposure. Acrylic resin outperforms polycarbonate for exterior applications, eliminating the need for UV coatings that add cost and complexity. This inherent weather resistance makes PMMA the preferred choice for automotive tail lights, outdoor signage, architectural glazing, and solar applications.
- Surface Hardness and Scratch Resistance: Rockwell M85-105 hardness exceeds most thermoplastics including polycarbonate, polystyrene, and polyethylene. The hard surface resists scratching during handling, assembly, and use. Parts accept polishing to restore optical quality after minor surface damage. This scratch resistance reduces maintenance requirements and extends service life for automotive instrument clusters, protective covers, and consumer products.
- Low Moisture Absorption: Water absorption of 0.2-0.3% in 24 hours ranks among the lowest of engineering thermoplastics. Lower moisture sensitivity compared to polycarbonate (0.12-0.35%) or nylon (1.5-3.0%) delivers more stable dimensions and fewer processing challenges. Parts maintain tight tolerances across varying humidity conditions. Reduced drying requirements simplify processing and lower manufacturing costs.
- Colorability and Aesthetics: PMMA accepts transparent, translucent, and opaque colorants while maintaining superior clarity and color brilliance. The material delivers vivid colors and special effects including metallics, pearls, and fluorescents with better depth and richness than polycarbonate. Excellent dye compatibility supports custom color matching for automotive, appliance, and consumer applications. The material maintains color stability during processing and extended UV exposure.
- Processing Versatility: Acrylic pellets process through injection molding, extrusion, blow molding, and thermoforming. Good melt flow enables thin walls, complex geometries, and tight tolerances. The material releases cleanly from mold surfaces with minimal sticking or tool buildup. Lower processing temperatures than polycarbonate reduce energy costs and cycle times. Secondary operations including machining, polishing, and bonding proceed without specialized equipment.
- Cost Effectiveness: PMMA typically costs 30-50% less than polycarbonate per pound while delivering superior optical performance. The material enables part consolidation and weight reduction compared to glass alternatives. Lower processing temperatures reduce energy consumption and equipment wear. The combination of material cost, processing efficiency, and performance delivers favorable total cost of ownership for high-volume applications.
Known Weaknesses
- Limited Impact Resistance: Notched Izod impact of 15-25 J/m falls significantly below polycarbonate (600-850 J/m). The material fractures under impact that PC would withstand. Brittle behavior at low temperatures restricts applications requiring high toughness. Impact-modified grades improve toughness to 100-400 J/m but sacrifice optical clarity. Applications involving potential impact require careful evaluation or specification of impact-modified grades.
- Heat Resistance Limitations: Continuous use temperature of 70-90 °C and heat deflection temperature of 85-105 °C limit high-temperature applications. The material softens and deforms at temperatures where polycarbonate (115-130 °C continuous use) maintains properties. Hot water contact above 80 °C causes distortion. Automotive under-hood, appliance, and industrial applications requiring sustained heat exposure exceed PMMA capabilities.
- Solvent Sensitivity: PMMA shows poor resistance to ketones, esters, chlorinated solvents, and aromatic hydrocarbons. Contact with acetone, MEK, methylene chloride, or toluene causes immediate softening, crazing, or dissolution. Alcohols at concentrations above 50% cause stress cracking. This chemical sensitivity complicates bonding, cleaning, and use in chemical environments. Applications must avoid these solvents throughout manufacturing and service life.
- Stress Cracking Tendency: Parts under load show susceptibility to environmental stress cracking when exposed to aggressive cleaning agents, alcohols, or marginal solvents. Internal stresses from molding or assembly accelerate cracking. Annealing reduces but does not eliminate ESC risk. Design must minimize sharp corners, stress concentrations, and press-fit assemblies. Applications requiring chemical cleaning or solvent exposure need careful material evaluation.
- Flammability: Standard PMMA burns readily with UL94 HB rating. The material requires flame retardant additives for applications demanding V-2 or V-0 ratings. Flame retardants reduce optical clarity and increase cost. Fire performance lags behind inherently flame-resistant polymers including polycarbonate, which achieves V-0 at lower additive loadings. Building codes and safety applications often require alternative materials or protective coatings.
- Processing Brittleness: The material exhibits notch sensitivity during molding, requiring generous radii and uniform wall thickness. Sharp corners or abrupt thickness changes cause stress concentrations and part failure. Ejection systems require careful design to prevent breakage. Post-molding operations including machining or drilling risk cracking without proper technique. These processing constraints increase tooling complexity and manufacturing costs compared to tougher polymers.
Operating Limits
- Temperature Range: Continuous use temperature of 70-90 °C represents the upper limit for sustained loading. Short-term excursions to 100-110 °C cause gradual property loss. Heat deflection at 85-105 °C defines the maximum temperature for dimensional stability under load. Applications requiring higher heat resistance should consider polycarbonate or heat-stabilized grades. Low temperature performance extends to -40 °C, though impact resistance decreases significantly below 0 °C.
- Chemical Environment: Avoid exposure to ketones, esters, aromatics, chlorinated solvents, and concentrated alcohols throughout the product lifecycle. These chemicals cause immediate softening, crazing, or stress cracking. Restrict alkaline cleaners to pH 8-11 and acidic cleaners to pH 3-6. Strong acids or bases above these limits attack the polymer backbone. Outdoor applications require UV-stabilized grades for long-term property retention.
- Mechanical Stress: Design stress limits remain below 20-25 MPa for long-term static loading. Higher stresses risk creep deformation over time. Impact loading requires 50-100% safety factors due to brittle fracture behavior. Avoid sharp corners, notches, and stress concentrations in part geometry. Press fits and interference assemblies need careful evaluation to prevent stress cracking. Applications involving repeated impact should specify impact-modified grades or consider alternative materials.
Typical Applications
- Automotive exterior lighting lenses and reflectors requiring optical clarity and UV resistance
- Automotive interior instrument clusters and center console displays using optical grade PMMA
- LED light guides and diffusers for backlighting applications
- Medical device housings and diagnostic component covers using USP Class VI acrylic resin
- Point-of-purchase displays and retail signage requiring outdoor durability
- Architectural glazing and skylights using UV-stabilized acrylic pellets
- Protective covers and safety shields for machinery and equipment
- Bathroom and plumbing fixtures requiring water resistance and clarity
- Consumer electronics housings and display covers
- Optical lenses and prisms for lighting and imaging systems
Niche Applications
- Aircraft canopies and windows using specialty high molecular weight grades
- Aquarium viewing panels and marine applications requiring long-term water contact
- Fiber optic light pipes and waveguides for telecommunications
- Solar panel covers and concentrators using UV-stable formulations
- Museum display cases requiring long-term clarity and UV filtering
- Dental prosthetics and orthodontic appliances using medical grade PMMA
- Refrigerator shelves and bins requiring food contact approval
- Traffic signal lenses and reflectors demanding outdoor weatherability
Design, Assembly & Aesthetics
Surface finish capability
PMMA accepts SPI A-1 to A-3 finishes delivering optical quality surfaces directly from the mold. The material reproduces fine textures, patterns, and gloss levels with high fidelity. Polished surfaces achieve mirror-like clarity without secondary operations. Textured finishes reduce visible defects and fingerprints while maintaining transparency. Lower surface energy compared to polycarbonate improves mold release and reduces cycle times.
Sink, warpage, and visible defect tendency
Amorphous structure and low shrinkage (0.3-0.7%) minimize sink marks and warpage compared to semi-crystalline polymers. Uniform cooling produces predictable part dimensions. Transparent grades show flow lines, weld lines, and air traps more readily than opaque materials. Gate location and runner design significantly impact optical quality. Proper mold temperature control and packing pressure reduce visible defects.
Colorability
Excellent acceptance of transparent, translucent, and opaque colorants. PMMA delivers vivid colors and depth superior to polycarbonate or polystyrene. The material accepts special effects including metallics, pearls, and fluorescents with exceptional brilliance. Transparent colors maintain clarity and lightness. Color matching proceeds reliably using standard masterbatch technology. UV exposure causes minimal color shift in stabilized grades.
Color stability
UV-stabilized acrylic pellets maintain color and clarity after years of outdoor exposure. Yellowing resistance exceeds polycarbonate by factors of 5-10. Transparent colors retain saturation and brilliance without fading. Heat exposure during processing or service causes minimal color shift. This color stability eliminates protective coatings for outdoor applications.
Optical properties and clarity
Light transmission of 90-92% and low haze (<1%) deliver glass-like clarity. Low birefringence in the amorphous structure prevents stress-induced optical distortion. Refractive index of 1.49 matches many adhesives and coatings for seamless optical joints. The material maintains clarity across varying wall thicknesses and part geometries. Optical grade PMMA meets specifications for precision lenses and light guides.
Scratch and chemical mar resistance
Surface hardness of Rockwell M85-105 resists scratching during handling and use. Hard coatings further improve abrasion resistance for demanding applications. Polishing restores clarity after minor surface damage. Chemical mar resistance depends on cleaner selection. Avoid alkaline cleaners above pH 11 and solvents including alcohols, ketones, and aromatics. Mild soap and water solutions provide safe cleaning.
Marking methods
Laser marking delivers permanent identification with excellent contrast. Pad printing and screen printing accept standard inks with proper surface preparation. Hot stamping produces decorative metallic finishes. Ink adhesion benefits from corona or flame treatment. In-mold decorating integrates graphics during molding. Avoid solvent-based inks containing ketones or aromatics that cause stress cracking.
Coating, painting, and plating suitability
Surface accepts coatings after proper preparation including sanding, chemical treatment, or plasma activation. Hard coatings improve scratch resistance. UV coatings provide additional weathering protection where required. Painting requires primers formulated for acrylic substrates. Vacuum metallization produces mirror-like finishes for reflectors and decorative applications. Chrome plating follows standard electroplating procedures with adhesion promoters.
Joining methods
Solvent bonding using methylene chloride, ethylene dichloride, or commercial acrylic cements produces strong, optically clear joints. Ultrasonic welding delivers fast assembly for simple geometries. Adhesive bonding using cyanoacrylates, epoxies, or urethanes supports complex assemblies. Mechanical fastening requires generous boss design and controlled torque to prevent stress cracking. Avoid press fits and interference joints in stressed areas.
Frequently Asked Questions
PMMA delivers superior optical clarity (90-92% light transmission vs 87-89% for PC) and better UV resistance without protective coatings. The material costs 30-50% less per pound and processes at lower temperatures. Polycarbonate offers significantly higher impact resistance (600-850 J/m vs 15-25 J/m for standard PMMA) and better heat resistance (115-130 °C continuous use vs 70-90 °C for PMMA). PMMA shows better scratch resistance and maintains outdoor clarity longer than PC.
Choose PMMA for applications prioritizing optical quality, weatherability, and cost effectiveness where impact requirements remain moderate. Select polycarbonate when impact resistance, heat resistance, and toughness outweigh optical performance and cost considerations.
Melt temperatures of 200-260 °C suit most PMMA grades. Lower temperatures (200-220 °C) reduce degradation risk and work well for thin-wall parts with good flow characteristics. Higher temperatures (240-260 °C) improve flow for thick sections and complex geometries requiring extended flow paths. Avoid melt temperatures above 270 °C to prevent degradation, yellowing, and monomer evolution.
Mold temperatures of 40-80 °C balance cycle time and part quality. Lower temperatures (40-50 °C) reduce cycles but increase internal stress. Higher temperatures (60-80 °C) improve surface finish, reduce stress, and deliver better optical quality. Optical applications requiring maximum clarity benefit from mold temperatures above 60 °C combined with controlled cooling rates.
Yes, despite lower moisture absorption (0.2-0.3% vs 0.12-0.35% for PC), PMMA requires pre-drying to prevent processing defects. Dry acrylic pellets at 70-85 °C for 2-4 hours in a desiccant dryer to achieve 0.02-0.04% moisture content. Higher drying temperatures above 90 °C risk monomer evolution and yellowing.
Insufficient drying causes splay marks, bubbles, surface blemishes, and reduced mechanical properties. Visible defects appear more readily in transparent PMMA than opaque polymers. Hopper dryers maintain dryness during processing in humid environments. The relatively low drying temperature and shorter time compared to polycarbonate (120 °C for 4-6 hours) simplify processing requirements.
Avoid contact with ketones (acetone, MEK), esters (ethyl acetate), chlorinated solvents (methylene chloride, trichloroethylene), aromatic hydrocarbons (benzene, toluene), and concentrated alcohols (methanol, isopropanol above 50%). These chemicals cause immediate softening, crazing, stress cracking, or dissolution.
Use mild soap and water solutions for cleaning. Isopropyl alcohol at concentrations below 30% provides safe cleaning for light contamination. Avoid alkaline cleaners above pH 11 and acidic cleaners below pH 3. Parts under mechanical stress show increased susceptibility to environmental stress cracking. Test any new cleaning agent on representative samples under actual stress and environmental conditions before production use.
Automotive lighting manufacturers benefit from superior optical clarity, UV resistance, and cost savings compared to polycarbonate. PMMA eliminates protective coatings for exterior lenses while delivering better light transmission. LED lighting companies leverage excellent light transmission and color stability for diffusers, light guides, and lens applications. Medical device manufacturers use USP Class VI acrylic resin for diagnostic equipment housings and fluid handling components where optical clarity and sterilization resistance matter.
Signage and display industries make use of acrylic’s outstanding weatherability for outdoor applications requiring years of exposure without yellowing or degradation. Architectural glazing projects use acrylic resin for skylights, windows, and panels requiring glass-like clarity at lower weight and cost. Consumer electronics manufacturers adopt PMMA for display covers and housings needing optical quality at competitive pricing. Each industry leverages the combination of optical performance, weather resistance, and cost effectiveness that distinguishes PMMA from alternative transparent polymers.
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