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CAP

Propionato de Acetato de Celulosa

CAP·Cellulosics·Amorphous

CAP (Cellulose Acetate Propionate) is the premium plastic of the eyewear world and one of the few thermoplastics that feels "warm to the touch" like a natural material. It's made from wood or cotton cellulose pulp —a bio-based feedstock— esterified with acetic and propionic acid. The leading name in the sector is Eastman Tenite Propionate (USA) for injection grades, and Mazzucchelli 1849 (Italy) as the world reference for extruded sheet used in spectacle frames. Eastman launched Tenite Renew as the sustainable version with recycled/bio-based content.

CAP's identity is defined by plasticizer level (typically 9-15%): lower plasticizer gives more rigidity, surface hardness, and heat resistance; higher plasticizer gives more impact strength and flexibility. It's hygroscopic —dry it at 65°C in a desiccant dryer with dew point -30 to -40°C before molding. Melt temperatures are moderate (185-215°C), making it easy to process.

Flagship applications: optical and sunglasses frames (Tom Ford, Persol, many premium brands), face shields and safety glasses (optical clarity with 1 mm walls), toothbrush handles, tool handles, cosmetic packaging, and automotive trim. Are you running CAP? Share your experience with plasticizers and frames in the comments.

The ranges shown in these data tables were compiled by the MVPS team from various parameter sheets and literature, integrating the lower and upper limits for each material type.

This information must be carefully reviewed when developing injection molding processes. Final ranges and processing tolerances are the responsibility of the engineer in charge.

These ranges are not recommended for developing specific process tolerances. MVPS always recommends requesting and consulting the supplier's data sheet.

General Properties

Chemical StructureAmorphous
Specific Gravity (Density)1.27:1
L/D Ratio18 – 24
Compression Ratio2 – 3
Tonnage Factor3.09 – 6.18kN/cm²
Thermal Diffusivity0.1171mm²/s
Max Shear Rate20,0001/s
Shrinkage0.3 – 1%
Regrind⚠ Caution
Heat Deflection (HDT) @ 1.82 MPa75°C
Glass Transition (Tg) @ 10°C/min149°C
Vicat Softening @ 50N96°C

Drying

Drying Temperature68 – 82°C
Drying Time2 – 6h
Recommended Moisture0.15%
Recommended Dryer TypeAir
Dew Point-40°C

Temperatures

Melt185 – 196°C
Nozzle185 – 196°C
Front185 – 196°C
Middle168 – 174°C
Rear154 – 160°C
Demolding77 – 93°C
Mold (Cooling)60 – 82°C
Feed Throat10 – 49°C

Processing

Back Pressure3.4 – 13.8bar
Screw Speed50 – 100RPM
Injection SpeedMedium
Barrel Occupancy25 – 75%
Injection Pressure700 – 1,500Pbar
Holding Pressure175 – 1,200Pbar
Cushion3.2 – 6.4mm

Mold

Runner Diameter3.3 – 6.1mm
Gate Diameter0.76 – 1.52mm
Gate Area0.46 – 1.82mm²
Wall Thickness0.8 – 3mm

Venting

Depth (Vent Depth)0.0203 – 0.0305mm
Land (Vent Land)0.508 – 0.762mm
Width (Vent / Clearance)3.05 – 6.1mm
Relief (Relief Channel)0.254 – 0.381mm

Frequently asked questions

CAP (Cellulose Acetate Propionate) is a **cellulose ester** —a bio-based thermoplastic made by treating cellulose pulp (from wood or cotton) with acetic and propionic acid. The backbone is still the natural glucose polymer of cellulose, but the hydroxyl groups are replaced by acetate and propionate groups, making it thermoplastic and processable. 9-15% plasticizer is added (typically non-BPA phthalates or alternative esters) for injection molding.
It combines five things no other plastic matches: **(1)** brilliant optical clarity, **(2)** ability to be colored in mass with marble, tortoise, gradient, and other patterns impossible in synthetic plastics, **(3)** **warm touch** —feels like horn or natural antler, not plastic, **(4)** ease of polishing and mechanical finishing (frames are machined from extruded sheets), **(5)** hypoallergenic (doesn't irritate skin unlike some synthetic thermoplastics). That's why brands like Persol, Tom Ford, or premium Ray-Ban use CAP or cellulose acetate.
**Pure CA** is the traditional "acetate" used for premium frames for 100 years —maximum optical clarity, maximum warm touch. But it's **brittle**, moisture-sensitive, and hard to process. **CAP** is the industrial evolution: it adds propionate groups that improve toughness, reduce moisture absorption, and enable direct injection molding (not just machining). For artisanal premium frames, CA still dominates; for mass production by injection, CAP wins.
**CAP** has a propionate group (3 carbons), is stiffer and harder, and requires more external plasticizer. **CAB** has a butyrate group (4 carbons), with **internal plasticization** —needs less added plasticizer, is more flexible and impact-resistant, and absorbs less moisture. **CAP** is used where optical rigidity matters (optical frames, face shields). **CAB** is used where flexibility and outdoor exposure matter (handles, outdoor parts, blister).
**Critical**: CAP absorbs atmospheric moisture and, if processed wet, gives silver streaks and bubbles. Dry it at **65°C for 2-4 hours** in a desiccant dryer with dew point between **-30°C and -40°C**. Ambient hot air doesn't work. In tropical climates or if the material has been open for days, drying is mandatory with no shortcuts.
Melt: **185-215°C** (lower than ABS or PC). Mold: **30-60°C**. The window is wide and the material doesn't degrade easily at these temperatures, but **don't sustain above 220°C** —it starts losing propionic acid and developing an acid smell. Moderate injection pressures (40-100 MPa). Medium-to-high injection speed to leverage the good flow.
**Yes, under the right conditions**, unlike petroleum-based plastics. Studies show significant degradation in industrial composting in **6-12 months** and measurable degradation in soil and water in 1-3 years. The parent cellulose chain is attacked by microorganisms. **Important note**: the added plasticizer may not be biodegradable, and color additives may not either. "Biodegradability" marketing is overhyped —use CAP for its properties, don't expect miraculous disappearance in regular trash.
Shrinkage **0.3-0.7%**, low and predictable —it's an amorphous material (no crystallization), with no significant directionality. That's one of the reasons it's good for optics: frames hold dimensional tolerances. For very thin-walled parts (1 mm face shields), actual shrinkage can drop to 0.2-0.4%.
**Moderately**. Better than pure CA but worse than PMMA or PC. For indoor and semi-indoor use (eyewear, handles, packaging) no problem. For continuous outdoor use, it yellows in 1-2 years without UV stabilizers. HALS-stabilized grades exist for moderate outdoor use. Equilibrium moisture absorption: **1-2%** (higher than polyolefins, similar to dry-as-molded Nylon).
**Yes, easily**. It's weldable by ultrasonic, vibration, and solvent welding (acetone, MEK). For adhesives, use cyanoacrylates, epoxies, or adhesives specific for cellulose-based plastics. For eyewear frames, hinge-to-front assembly is typically done by hot embedding: the material softens at low temperature and is molded around the metal hinge, which makes it an exquisite material for mixed-component assembly.

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