Tech Talk Blog

For removing excess adhesive during the bonding process we do NOT recommend using any solvents. Some of the solvent can migrate under the Rulon and destroy the bond on the edges – may cause a lifting up of the material when under load in the application. We recommend instead waiting until the adhesive dries and then scraping off the excess, or in some cases we use a belt sander if enough space is available to use it effectively. Alternatively, if we do not want to generate that kind of dust, and to keep the finished parts clean, we will mask off any areas where the excess adhesive can be a problem, and then just peel the masking material off after the glue has dried.

For removing old Rulon, or other similar PTFE material, so that new material and adhesive can be applied, heat the part up to approximately 250 degrees F. That breaks the adhesive bond and you then can peel off the Rulon that is remaining. Then you can scrape off the remaining old adhesive or sandblast it. Sandblasting leaves a good surface for rebonding new material to. If there is very little Rulon left, and the flatness of the metal is critical, then we suggest milling off the old material. Again, the swirls from the milling operation provide an excellent surface to bond new material to.

Acrylic or poly(methyl 2-methylpropenoate) is a specific group of thermoplastics. Methyl methacrylate is polymerized in bulk or suspension methods using free-radical initiators.

PMMA - polymer chain

The presence of the pendant methyl (CH₃) groups prevents the polymer chains from packing closely in a crystalline fashion and from rotating freely around the carbon-carbon bonds. As a result, PMMA is strong, transparent and somewhat inert.

Bonding untreated PMMA to itself is limited to either cyanoacrylate, dichloromethane (CH₂Cl₂), or trichloromethane (CHCl₃). The bond strength using these methods is strong and can exceed the strength of the acrylic substrates. Unfortunately, these adhesive may not be effective when bonding acrylic to other materials. When acrylic is to be bonded to materials other than itself, plasma treatment can assist in enhancing the bond strength.

A plasma is a quasineutral cloud of ion, electrons, and radicals. The diffuse cloud is capable of doing chemistry on the surface of materials that is unique, providing wettable or adherent surfaces on materials that are otherwise inert.

The PMMA samples in this study were subjected to a specific plasma gas mixture to induce and adherent surface for a structural epoxy adhesive. The results are as follows:

In summary, PMMA can be bonded using mechanical or solvent chemical methods. Yet, it has been proven that plasma surface modification is a viable, environmentally friendly, invisible treatment that can enhance the bonding performance significantly. For more informtion about this process please contact us at our Tristar Plasitics Corp. website.

Using simple plasma surface modification techniques, we are able to manipulate the surface of most plastic devices to contain fluids or direct flow.

Surface treatment zone

the surface treatment zone shown in the picture above is 0.9mm. The wet zones are hydrophilic drawing water into the narrow zone while the other areas are hydrophobic to the natural polystyrene material.

If you would like more information about this process, please vist our website.

There are two primary reasons that dye fades:

1.) The dye is loosely attached into a device and “falls out”. A good analogy to visualize this effect is water on a screen door. Visualize the dye as the water and the screen as the polymer.The dye will remain in place until the polymer is stressed; like snapping the wet screen.

2.) The dye molecules are ‘excited” by UV and combine on contact with the oxygen in the air. In other words they are pulled out of the material by a chemical reaction that occurs normally.

Dyes can also fade to some extent due to the heating of the polymer in hot weather conditions, perspiration and cleaning. Most customers are instructed to wash polymers in warm, soapy water. When the lenses are cleaned the top most layer of the dye molecules is wiped away. You can reduce the effect of the first, but can do nothing to prevent the second. Unless a clear top coat from TriStar Plastic’s product line is used. To discuss your particular needs, please visit our website Tristar Plastics.

The expansion due to applied heat under ideal circumstances will occur in three dimensions, but with thin film flexible substrates, a mismatch in the coefficient of thermal expansion will result in interfacial stress causing curl.

Case 1.  The coating has a higher coefficient of thermal expansion vs. the substrate:

Case 2.  The coating has a lower coefficient of thermal expansion vs. the substrate:

Case 3. Coatings of relatively higher modulus may respond to interfacial stress to the extent that any substrate thermal expansion will cause cracking, crazing, and loss of adhesion.  Such failure may not occur until the system has been repeatedly cycled through extremes of temperature.

Benzene ring Structures

• The benzene ring acts as a electron bank loaning and accepting electrons
• Polymers with benzene rings include PS, PET, PU, PC and PSU
• Polystyrene is stable

 Amorphous Polymers

• Highly amorphous materials (non crystalline) are generally resistant to radiation since the chain structure is capable of great ductility and they can tolerate many scissions without breaking up

 Polyamides (Nylons)

• Nylons especially aromatics 12, 11, 6/12, 6/10 are highly resistant to irradiation
• Nylon 6 is least radiation resistant

 Butyl Rubber

• Natural rubber survives irradiation very well but butyl rubber crosslinks to become stiffer, loses elongation and turns friable and powdery
• For this reason butylene -containing polymers such as ABS and PBT loses impact strength on irradiation

 Stress Cracking

• A polymer under stress is attacked more by radiation than unstressed material is.
• Scissioning and oxidation effects are concentrated in the stressed zones
• Therefore plastic parts must have reproducible molded-in stresses

 Key Messages

• Aromatic polymers (e.g. with benzene rings) are more stables than aliphatic chains
• Look at ratio of scissioning to crosslinking
• Most natural PP and PTFE are unstable with irradiation

Survey Exposure

• If it is difficult to predict how a polymer system will resist irradiation (e.g. by accelerated ageing) then the use of an exaggerated dosing at 100 kGy should highlight problems and marginal materials

If you are unsure if your material will hold up to this sterilization technique, please visit the TriStar Plastics Corp. website for contact information.

Gamma Radiation is commonly used to sterilize polymer devices. But some polymers do not hold up well to this form of sterilization.

The following plastics cannot be sterilized by radiation:

• Polyacetals (turns to dust)
• Polyacetals(turns to dust)
• Polypropylene (unstabilized)
• Teflon (turns to wax)
• PVDF

Polypropylene Syndrome

• Natural unstabilized PP undergoes a slow degradation process after irradiation where over two years the elongation may drop from 600% to zero and parts will shatter
• PP is both crosslinked and scissioned
• Embrittlement and discoloration can occur
• Radiation stable PP is available

 Polyethylene

• Polyethylene is predominantly crosslinked but acceptable to irradiation
• LDPE < LLDPE < HDPE < UHMWHDPE
• PE can be stabilized to make it gamma stable

If you are unsure if your material will hold up to this sterilization technique, please visit the TriStar Plastics Corp. website for contact information.