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Adhesives forDifficult-to-bondPlasticsA

GU

IDE

TO

@CraftechIndNY

/company/craftech-industries

info@craftechind.com

www.craftechind.com

info.craftechind.com/blog

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Many modern plastics are formulated specifically to be anti-corrosive in specific chemical and environmental conditions. As a result, these polymers also tend to be difficult to chemically bond because of their low surface energies, low porosity, and non-polar or non-functional surfaces. They feature no functional site or surface roughness onto which an adhesive can secure itself. In other words, they are extremely smooth and slippery, so there’s nothing for the glue to grab onto.

Being able to effectively bond two surfaces together can

be useful in many situations. Yet, few adhesives offer consistently

high bond strengths. In order to steer you towards the best adhesives

on the market, we’ve expanded our list of glues (and plastics!) since

our last blog post on the subject.

We tested the bonding capabilities of various glues that purport to

be compatible with some of the most difficult-to-bond polymers. We

tried sticking each sample of plastics (listed right) to itself and after a

24-hour curing time we attempted to break the pieces apart to

determine which glues worked best. Read on for our results!

Teflon (PTFE) »A synthetic fluoropolymer characterized by its excellent dielectric properties, high melting temperature, and non-reactivity. Teflon has one of the lowest coefficients of friction in the world of plastics

Polyethylene »A thermoplastic with high impact resistance, low density, and good toughness. This plastic is especially useful where moisture resistance and low cost are required.

Polypropylene »A thermoplastic polymer that is rugged and unusually resistant to many chemical solvents, bases and acids, making it useful in a wide variety of applications.

Polyurethane »An elastomeric material of exceptional physical properties including toughness, flexibility, and resistance to abrasion and temperature. It combines the toughness of metal with the elasticity of rubber.

Nylon »A commonly used synthetic polymer because of good mechanical properties, wear resistance and high melting point. Nylon is frequently used when a low cost, high mechanical strength, rigid and stable material is required.

Lexan »An amorphous polycarbonate polymer that offers a unique combination of stiffness, hardness and toughness. It exhibits excellent weathering, creep, impact, optical, electrical and thermal properties.

What makes these plastics so difficult to bond?

Objective

Materials

DISCLAIMER: The information listed here is intended as a guide only. Companies should do their own testing when using the above materials. Craftech Industries cannot be held responsible for any of the information listed here.

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LOCT

ITE®

Plastics Bonding System »

Our ResultsThe Loctite Plastics Bonding System was the easiest

glue to use. After priming and gluing the samples

together, we let them cure for 24 hours then attempted

to break the bond created. The plastic sounded like it

splintered as we broke the bonds, however we were not

able to break apart the Lexan or Polyurethane samples.

NB: This adhesive caused clouding and discoloration

on our Lexan sample, indicating a chemical reaction. If

appearance is a concern, make sure to always test any

glue on a piece of scrap material.

A two-part cyanoacrylate adhesive that sets in seconds and doesn’t require clamping. It’s quick, easy, and Loctite boasts its effectiveness on hard to bond plastics such as Plexiglass™, polycarbonate, polystyrene, PVC, polyethylene and polypropylene.[ ]

TECH

BO

ND BP Blue »

What is cyanoacrylate and how does it work?Our Results

We were excited to try out this adhesive because the

manufacturers boasted that their product was the solution to

bonding hard-to-bond plastics. For our first attempt, we left

the plastics untreated and didn’t roughen the surface with any

kind of wire scrub or sandpaper. After twenty-four hours of

curing, all of the plastics broke apart with ease. However, after

sanding, this adhesive bonded all of our samples perfectly.

Even wedging a screwdriver into slight gaps between the

pieces didn’t work!

Cyanoacrylate is more commonly referred to as superglue and hardens very quickly when trapped between two surfaces. The reaction is caused by the condensed water vapor on the surfaces, so humidity is a factor that may affect bonding capabilities. Cyanoacrylate is ideal for a tight join between two stationary parts and the bond seems to weaken if exposed repeatedly to temperature changes, so it is not ideal for outdoor or mechanical use.

A one-step cyanoacrylate solution engineered to bond with polymer strings, quickly, easily and permanently. It creates a molecular bond which provides a stronger, more durable result. [ ]

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LOCT

ITE®

J-

B W

ELD

Epoxy Plastic Bonder »

PlasticWeld »

What is epoxy and how does it work?Our Results

Our first try with this adhesive proved a failure because we missed

the crucial step of sanding the plastic with 220 grit sandpaper to

roughen the surface. However, after sanding and re-gluing the

pieces, it became quite a challenge to break them apart. We only

managed to break apart the polyurethane sample after wedging

a screwdriver into a small space between the layered pieces and

even then it was quite a bit of work to manage to break the bond.

The other samples held together well, even though the epoxy

wasn’t recommended for polyethylene, polypropylene, Teflon™

or other non-stick surfaces.

Our ResultsThis adhesrive also called for roughening the surface

with sandpaper to give the glue some added grip. The

PlasticWeld worked well on our samples. It spread

to create a gap-free bond, filling in all the available

space for strong adhesion that just wouldn’t quit,

even after we tried desperately to separate the parts.

NB: We recommend wearing a face mask when

using the PlasticWeld as the chemical smell was

quite powerful.

Epoxy is also known as polyepoxide. It is basically a thermosetting polymer created by a manual reaction of a resin and a hardener; where the resin is an epoxide and the hardener is a polyamine. Epoxy resin and epoxy hardener are mixed together to different ratios depending upon the needs of the user. The more the hardener is added, the more time it takes to set. Hardener makes the whole compound stronger. Epoxy is resistant to water and can even cure underwater.

An acrylic formula that is specially formulated to bond and repair plastic surfaces. The double syringe dispenses equal amounts of each component which produces a tough, rigid, high strength bond in 20 to 25 minutes with a full cure in twenty-four hours. ]

A hand-mixable, fast-setting epoxy putty that forms a durable bond to most major plastic types. It has a 20-25 minute work life with a functional cure in 2-3 hours. It is not recommended for polyethylene, polypropylene or some other plastics.[ ]

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PLEX

US®

3M

™MA310 Adhesive »

Scotch-Weld™ DP8010 »

What is methacrylate and how does it work?Our Results

The MA310 is not for someone on a strict budget.

This adhesive required the purchase of an applicator

gun, mixing nozzles, and the correct ratio plunger.

If you have all these materials, then applying the

MA310 is a breeze. For this adhesive, we sanded and

clamped the samples and, after the 24 hours, trying

to break the bond created proved to be extremely

difficult. We were not able to break the samples of

any of our plastics apart.

Our ResultsThis structural adhesive also requires the use of an

applicator gun, mixing nozzles, and the correct ratio

plunger. Even though the directions said we did not have

to roughen the surface, we did anyway just to improve

the chances of a strong bond. Again, we obtained perfect

results. Even Teflon, a notoriously slippery material,

bonded tightly to itself. The soft plastic even chipped

when we tried to break the bond.

Methacrylate adhesives, also referred to as acrylic adhesives, are incredibly strong and easy to use. Once the curing agent and resin are mixed, they chemically react to form chemical chains that bind with each other and certain surfaces, particularly plastics and metals. Unlike epoxies, thorough mixing is not as crucial and, once the chemical reaction initiates, the rate of reaction increases to provide more rapid strength build-up.

A two-part methacrylate adhesive designed for structural bonding of thermoplastic, metal and composite assemblies. Combined at a 1:1 ratio, it has a working time of 15 to 18 minutes and achieves a rapid fixture in 30 to 35 minutes at room temperature. Particularly well suited for bonding thermoplastic materials, the MA310 combines high strength and stiffness with the ability to adhere difficult-to-bond materials. Supplied in ready-to-use cartridges.

Two-part acrylic based adhesive with a 10:1 ratio that provides high quality bonding performance on most low surface energy plastics including polypropylene, polyethylene and thermoplastic olefins without surface treatment. [ ]

[ ]

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STA

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ZIN

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OO

PHot Glue Gun »

All Purpose Adhesive »

What is hot melt adhesive and how does it work?

Our ResultsWe used two different types of hot melt adhesives, all-purpose glue

sticks and Formula II super strength glue sticks. Both sticks had a

hit or miss success rate. After 24 hours, Teflon and polyethylene split

pretty easily. Polyurethane didn’t create a bond at all. Polypropylene

was a bit more successful. While we were still able to break the bond, it

was very difficult. The hot melt adhesive was most effective on nylon,

which we were able to break after a lot of effort and maneuvering with

a screwdriver wedged between the two pieces, and Lexan, which we

were not able to break at all. There didn’t seem to be any difference

between the all-purpose and the Formula II super strength glues, as

each yielded the same results on the samples.

Our ResultsThis adhesive created a bond that worked like elastic.

As we attempted to break the pieces apart, the glue

snapped them back into place until the bond was

completely severed. It was very difficult, but in the

end we were able to separate all the pieces.

Additionally, the Amazing Goop lived up to its name:

it is extremely goopy, making it less than ideal for

small, delicate projects.

Hot melt adhesives contain a wide range of elements, including ethylene-vinyl acetate, wax, resin and any assortment of polyamide, poly-ethylene, polyester or polypropylene. In industrial use, hot melt adhesives provide several advantages over solvent-based adhesives. Volatile organic compounds are reduced or eliminated and the drying or curing step is eliminated. Hot melt adhesives have a long shelf life and usually can be disposed of without special precautions. Some of the disadvantages involve thermal load of the polymer, limiting use to polymers not sensitive to higher temperatures, and loss of bond strength at higher temperatures, up to complete melting of the adhesive.

A form of thermoplastic adhesive that is commonly supplied in solid cylindrical sticks of various diameters. The glue squeezed out of the heated nozzle is initially hot enough to burn and blister skin, so use with caution. The glue is tacky when hot, and solidifies in a few seconds to one minute. It does not lose thickness during solidifying.[ ]

Scientifically formulated to repair, seal and stick to a wide variety of materials with superior strength to any other brand. Does not become brittle in cold weather. Good for bonding items subject to vibration. Safe for applications exposed to dilute acids and dilute caustics.[ ]

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After sticking everything togehter (even our fingers) we’ve found the best adhesives to use on those pesky plastics and the winners seem to be J-B Weld, Plexus, and 3M!*

What is the best adhesive for hard-to-bond plastics?

Lexan Teflon Nylon Polypropylene Polyurethane Polyethylene

Tech Bond BP Blue very strong very strong very strong very strong very strong very strong

Loctite Bonding System strong weak weak weak strong weak

Loctite Epoxy strong strong strong strong decent strong

J-B Weld Plasticweld very strong very strong very strong very strong very strong very strong

Plexus MA310 very strong very strong very strong very strong very strong very strong

3M Scotch-Weld DP8010 very strong very strong very strong very strong very strong very strong

Hot Glue Gun very strong weak strong relatively strong no bond created weak

Amazing Goop decent decent decent decent decent decent

Adhesive Base Curing Time Tensile Strength Temp Guidelines

Tech Bond BP Blue Modified Ethyl 24 hours 13053 to 18854 psi -65° F to 220° F

Loctite Bonding System Ethyl Cyanoacrylate 24 hours 290 to 2900 psi up to 180° F

Loctite Epoxy Methyl Methacrylate 24 hours 2903 to 3477 psi -40° F to 180° F

J-B Weld Plasticweld Epichlorohydrin & Bisphenol A 1 hour 3200 psi -67° F to 500°F

Plexus MA310 Methacrylate 30 - 35 minutes 3988 to 4496 psi -67° F to 249° F

3M Scotch-Weld DP8010 Acrylic 8 - 24 hours 2400 psi -20°F to 180°F

Hot Glue Gun Ethylene Vinyl Acetate 60 seconds 391 psi 0° F to 359° F

Amazing Goop Silicone 24 to 72 hours 3800 psi -40°F to 150°F

Technical dataBond strength

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Adhesive Comparison Chart »

THIS CHART WAS TAKEN FROM PLEXUS® GUIDE TO BONDING.*

Advantages Limitations

» Moderately priced » Good gap-filling capabilities » Rigid to flexible bonds available » Versatile formulations » Fast setting

» Usually low strength » Poor gap cure » Poor creep resistance » Many must be applied to both surfaces » Poor temperature, moisture, and solvent resistance » Attack many plastics » Flammable » Environmentally unfriendly

» Usually low priced » Good gap filling capabilities » High strength: can be filled with metals » Wide range of formulations » Versatile » Good temperature and solvent resistance

» Adhesives thin during curing cycles » Two component mixing and measuring required » Exact proportions needed for optimal strength » Slow fixturing » Short pot life creates waste » Special equipment needed to weigh, mix and dispense

» Rapid cure at room temperature » Single component adhesive » Excellent adhesion to rubber » Good adhesion to metal » High Tensile strength » No mixing required » Indefinite pot life » Dispense easily from package

» Higher priced » Limited gap cure » Low solvent resistance » Low temperature resistance » Bonds skin » Poor impact and peel resistance » No water, chemical or environmental resitance

» Moderately priced » Good gap fill » Excellent impact resistance and flexibility » Excellent peel and shear strengths » Substrate versatility » Medium/fast cure » Tolerant of dirty surfaces » Can be dispensed from most packages » Good flexibility at low temperatures

» Some odor problems » Flammable