Delrin® Homopolymer Acetal compared with Acetal Copolymer
Many of our clients assume that Delrin® rod and Acetal rod are the same thing. This is not true.
Yes, all Dupont Delrin® rod is Homopolymer Acetal rod, but not all Acetal rod is Delrin® rod.
Delrin® is the trade name for Homopolymer Acetal made by Dupont. Dupont™ Delrin ® is a popular acetal homopolymer brand name and the most commonly used acetal homopolymer.
This is the most recognized of all trade names for Acetal materials, but not the only available Acetal material. The Copolymer Acetal resin is produced by a wide variety of large plastic manufacturers, BASF is probably one of the largest and most well known. Some main resin names are: BASF Ultraform® H4320, Kepital® F10-02, Hostaform® M25 and many others.
While Delrin® Homopolymer Acetal is a wonderful material, in a larger cross sections Homopolymer can exhibit center line porosity, or ‘soft centers’. This can sometimes be seen with the naked eye, and is a darker white in a normally milky white natural colored material. This center line porosity can cause problems in some applications. This porosity can cause leakage of fluid if under pressure, or soft center’s of homopolymer rod and sheet.
This should not stop you from considering Delrin® Homopolymer Acetal though. Many other properties of the homopolymer resins are superior to the copolymer resins. These properties are:
General Property
ASTM Test
Typical Value Unfilled Homo-Polymer
Typical Value Unfilled Co-Polymer
Specific Gravity
D792
1.42
1.40
Tensile Strength Yield
D638
9,600 – 11,000
9,000 – 10,200
Tensile Modulus
D638
450,000
400,000
Izod Impact – Notched
D256
1.2
1.0
Hardness – Rockwell
D785
M94
M90
Deflection Temp @ 264psi
D648
257
220
Deflection Temp @ 66 psi
D648
347
335
Water Absorption @ 24 hrs
%
0.24
0.25
Co. Thermal Expansion
D696
6.83X10-5
5.4X10-5
Some key properties for homopolymer acetal are: higher tensile strength, increased Izod impact, higher deflection temperatures and it is slightly harder. The co-efficient of thermal expansion is a bit higher, and needs to be considered when designing a new part. Extruded Delrin® brand homopolymer resin material also comes in several resin variations, including: Delrin® 150 and Delrin® 507, contact us for details. Dupont™ Delrin® is a popular acetal homopolymer brand name and the most commonly used acetal homopolymer.
Many of our clients prefer the homopolymer rod and sheet for small machined parts. This is due to the increase in a few key properties, and of course brand recognition. Some of our major brand names for quality Copolymer Acetal (POM-C) sheet and Rod include: Tecaform AH®, Sustarin C®, ZL 900® and Pomalux®.
Both resins meet the standard ASTM-D-6778, and the cancelled specs, L-P-395 and ASTM-D-4181. Contact us for certification and specifications you may require.
The Acetal family of plastic resins are excellent for wear resistance, great mechanical strength, and superior machining properties. It is available in a huge range of sizes and shapes. Click here for more details on Acetal – Homopolymer Acetal Rod, and sometimes referred to as plastic dowel. We also have the capacity to supply colored Acetal Copolymer or Delrin® Homopolymer Acetal rod; click here from more details on the colored Acetal material.
Similar materials to Acetal Copolymer – Homopolymer Acetal are Nylon Rod, PET Rod and Noryl® Rod. Most materials are available as round rod, square rod, bar, strip, sheet and plate.
Please contact us for more details on these and other plastic materials. For a comparison chart of plastic materials click here: Plastic Materials Selection Guide
**Note: Delrin® is a registered Trademark of Dupont
A newly released form of Filled PEEK is now available. This PEEK is filled with PTFE and is called Unitrex Lf20, and it is filled with 20% PTFE. This new grade of PTFE Filled PEEK plastic was originally produced by Nytef Plastics. It is an extruded thermoplastic that comes in both rod and sheet form. This grade has significantly improved properties over the standard unfilled grades of PEEK. The PTFE filler provides excellent wear properties and has a very low co-efficient of friction, which makes this a great material for sliding and wear applications, and is made to last for long periods of abuse. Unitrex Lf20 has great machinability and dimensionally stability. It has a wide range of uses in such fields as medical, semi-conductor, and aerospace seals, where standard PEEK is too rigid. These properties enable this material to replace Polyimide (Vespel®) and PCTFE (formerly Kel-F) in many applications of high chemical resistance and the ductility for use in seals. This Filled PEEK works extremely well in Medical, Semi-Conductor and Aerospace Seal applications.
PTFE Filled PEEK vs. PTFE Filled Acetal
Comparable to Lf13 which is 13% PTFE filled Delrin® (Delrin® AF), which is also good for most of the same types of applications but cannot withstand the high temperatures than that of Unitrex Lf20. The PTFE Filled PEEK has a melting point of 650 degrees F while the PTFE Filled Delrin® – Unital® Lf13 has a melt point of 347 degrees F, making both materials high temperature plastics.
Because the Nytef Unitrex Lf20 is filled with PTFE (which has the lowest co-efficient of friction of any plastic), it is ideal for sliding and wear applications. It also has a kinetic and static friction resistance of 0.1 which makes it the perfect choice for jobs were heat from friction should not be generated and part longevity is critical. Unitrex Lf20 offers superior properties to many other plastics, such as high heat and chemical resistance but also great friction resistance along with improved properties to make it a great plastic for a wide spectrum of uses.
Why Change from Vespel SP-1 or PCTFE to Unitrex Lf20?
While this new PTFE Filled PEEK will not replace the Vespel SP-1 and PCTFE in all applications, it certainly will in many applications (see table for comparison). The main reason to make a change is, drum roll please, COST. The Unitrex Lf20 is up to 30% less expensive that the other materials. With similar and comparable properties, consider making the change.
Unitrex® Lf20 also exhibits a far superior chemical resistance to that of its Acetal counterpart due to PEEK having a far better range of chemical resistance to aqueous and organic environments as well as acids and alkalines. Acetal Copolymer tends to degrade when exposed to such chemicals like sulfuric acid and chlorine while PEEK only tends to be attacked by halogens and hydrocarbons such as in crude oils. For additional properties and to compare the Unitrex LF-20 to Dupont Vespel SP-1 and PCTFE see the table below. Here is a copy of the full data sheet on Nytef Unitrex Lf20.
Standard Properties Table
Properties
TestMethod
Unit
UnitrexLF20 Nominal Value
PCTFE(Kel-f) Nominal Value
VespelSP-1 Nominal Value
Specific Gravity
ASTM-D-792
1.42
2.1 – 2.14
1.43
Tensile Strength
ASTM-D-638
psi
11,500
4,800 – 5,300
12,500
Tensile Modulus
ASTM-D-638
psi
460,000
207,000
–
Flexural Modulus
ASTM-D-790
psi
500,000
180,000
450,000
Rockwell Hardness
ASTM-D-785
84-D
90-D
45 – 60 E
Melting Point
DSC
degress F
650
410 – 415
680+
Flammability
UL 94
@ 3.0mm
V-0
V-0
V-0
Kinetic Coef. of Friction
ASTM-D-1894
0.1
–
–
Static Coef. of Friction
ASTM-D-1894
0.1
–
–
For additional details on these and other materials, please contact us here or call us at 866-832-9315
Unitrex and Unital are registered trademarks of Polymer Industries Delrin and Vespel are registered trademarks of E.I. Dupont
