Consumers often choose plastic fasteners for their good chemical and acid resistance, non-conductivity, and tolerance of water exposure.  Although popular, plastic fasteners are generally not known for their strength.

Despite this reputation, there are plastic materials that have all of the better-known characteristics of plastics and yet rival the strength of metals. 

Does your application require strength as well as non-corrosive and non-conductive properties?   Check out the top three strongest plastic fastener materials.

1.       FR-4/G10

FR-4/G10  is a composite material made up of woven fiberglass cloth and an epoxy resin.  This combination gives the laminate good strength to weight ratios.  Typical physical and electrical properties of FR-4 are expressed by LW (length wise, wrap yarn direction), and CW (cross wise, fill yarn direction).   LW and CW refer  to fiber orientations that are perpendicular to each other. With a tensile strength of 45,000 psi  (310MPa), FR-4 plastic fasteners compare favorably to brass and aluminum.  Aluminum (Grade 6463-T6) has an ultimate tensile strength of 35,000 psi (241 MPA) and the number for free machining brass (Grade C3600)  is 50,000 psi (345 MPA). 

FR-4 plastic fasteners are flame resistant.  Flame resistant means that the parts are self- extinguishing according to the UL 94 test.  G10 plastic fasteners are not flame resistant and are no longer commonly used, although they are still used in applications where thermal destruction of the material is desirable.  FR-4 epoxy resin typically uses bromine, a halogen, to give the material a UL 94 V-0 flammability ratingFlame retardant and with near zero water absorption, FR-4 plastic fasteners retain their high mechanical strength and electrical insulating qualities in both dry and humid conditions.  FR-4 is not available in injection molding grades but rather in sheets, plates and rods.

FR-4 is the insulating backbone of printed circuit boards (PCBs) and is also used for bushings, washers, screws, bolts, nuts, switches, standoffs, threaded rod and transformers.

2 .     Polyarylamide (PARA)

Polyarylamide (PARA) contains a base resin that has lower and slower water absorption than typical polyamides.  This resistance to water absorption is attributable to PARA’s semi-aromtic structure.  Polyarylamide compounds reinforced with  glass fiber result in plastic fasteners that have very high rigidity, excellent surface quality, extremely low creep*  and high dimensionally stability.  PARA 50% glass reinforced material is resistant to a variety of chemicals including those used in the automotive industry.

With an ultimate tensile strength of 34,000 psi (230MPa), PARA 50% glass-filled plastic fasteners are often used to replace metal.  Available in a wide variety of colors, PARA is often used in the covers for cell phones and other electronic devices as well as aircraft and automotive applications, furniture, small appliances, power tools, camera components, bushings, gears, handles, hinges and knobs.

PARA 50% glass-filled is sold under the brand name of IXEF®, among others. 

3.      Thermoplastics Polyurethane (TPU)

Thermoplastic Polyurethane is an impact modified amorphous polymer*** with the chemical resistance of crystalline resins.  TPU has a low uniform shrink rate which allows to minimal creep*.  TPU 40% glass filled plastic fasteners are significantly lighter than metal fasteners.  With an ultimate tensile strength of 27,000 psi (186 MPa), TPU 40% glass-filled is comparable to aluminum.   With strength, moisture and chemical resistance, low creep and UV resistance, TPU 40% glass fiber is an ideal material for plastic fasteners used in applications such as internal scaffolding products, beam clamps, pipe hangers , post bases, bolts, hex nuts, pipe clamps, clevis hangers, channel nuts, U-bolts, and more.

TPU 40% glass filled is sold under the brand name Isoplast®, among others.

Ultimate Tensile Strength

Material Mpa PSI
FR-4/G-10 310 44,960
PARA (50% glass-filled) 230 33,358
TPU (40% glass-filled) 186 29,977
Magnesium (Grade HK31A-T6) 225 32,633
Brass (Grade C3600) 345 50,000
Zinc Alloy 280 40,610
Aluminum (Grade 6463-T6) 241 35,000
Steel 330 47,862

 

*Creep is the tendency of a solid material to move slowly or deform permanently under the influence of stresses.

**An impact modified polymer is one whose impact resistance and toughness has been increased by the incorporation of the phase microdomains of a rubbery material.

*** An amorphous polymer has a molecular structure that lacks a definite repeating form.

Looking for more material property information?  Check out our full Guide to High Strength Engineering Plastics!  Click the button below.

 

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