Problems Bonding Plastics

Do you know that you often require a third substance, the adhesive, to link pieces in a bonded junction for normal assembly operations where you glue plastic to plastic or other material parts?

Adhesive users know that bond failures can happen, but they might not know about the causes. Often the lack of detailed instructions from adhesive manufacturers on surface preparation before bonding is a major reason of bond failures.


What are the challenges in bonding plastics?

Users can easily stop failures and form solid, long-lasting bindings by knowing about the composition of surfaces and how to prepare them properly.


1. Contamination 

The kind and degree of contamination on the bond surface can greatly influence whether or not the bonding process will be successful. The specifics of cleaning and surface preparation are essential and usually depend on the substrate.

2. Detailed knowledge

Users can easily avoid failures and form solid, long-lasting bindings by knowing about the composition of surfaces and how to prepare them properly. The specifics of cleaning and surface preparation are essential and usually depend on the substrate. They may also be particular to the source since different suppliers’ materials will often have varying levels and types of impurities, requiring various surface preparation methods to get a suitable bond surface.

3. Surface Treatments

Certain bonding applications require the usage of plastics, which are quite challenging to bind. Applying a surface preparation is required in these situations to do the adhesive work properly.

4. Roughening the plastic Surface

Most adhesive data sheets to form a good bond include instructions to “roughen the surface,” The instructions typically indicate that roughness is an important part of a bond surface.

The importance of making the surface exceptionally clean is greater than that of roughening. Additionally, cleaning must be done before any roughening steps. 


How is plastic bonded?

Here are several external factors that you should consider to properly bond plastics:

  • The adhesive must meet the primary material criteria for the planned application in terms of compliance (such as food compliance) and mechanical qualities.
  • When bonding plastic, you should consider thermal and chemical factors.
  • Finally, it is important to consider technological requirements, including surface pre-treatment and the time of adhesive application.

Please keep in mind that amorphous polymers have the risk of stress cracking. Plastics must always be pre-treated before joining.

(It is often better to have complete information from the glue provider to help select the optimum adhesive. Specific testing should be carried out for any project involving the bonding of polymers.


What you need to know about bonding plastics

Seven families of adhesives are most frequently used to join plastics. Each provides a special mix of processing and performance advantages.

  • Cyanoacrylates
  • Light-cure Acrylics 
  • Light-cure Cyanoacrylate 
  • Hot-melt glues
  • Epoxies
  • Polyurethanes
  • Two-part acrylics


What is the best to bond plastic?

Plastics may be permanently attached to one another or other materials thanks to bonding technology, which is a very effective joining technique. The best way to bind plastic is by chemical joining or bonding.


What is the importance of bonding plastics?

When compared to alternative joining techniques, chemical joining (bonding) of plastics have several advantages:

  • Even stress distribution 
  • No material damage
  • No linked parts’ warping
  • Various material combinations can be connected.
  • The joint is simultaneously sealed.
  • There are fewer parts needed.
  • They connect surfaces with uneven shapes more readily than mechanical or thermal fastening.

Guideline for bonding plastic:

  • Selecting the right mechanism, preparing the surface finish, and following a few basic guidelines are the first steps in securely bonding plastics.
  • Check the mechanical, primer, and thermal characteristics of the substrate and the plastic to ensure they are correctly prepared.
  • After cleaning the substrate, clean it one more time! Even a tiny bit of dirt or oil remaining on the surface might stop a proper bonding process.
  • Prove that the glue and the plastic are compatible. Amorphous (see-through) polymers may haze and break when exposed to certain adhesives.
  • We advise against using fast-cure adhesives since they will likely break after 24 hours of curing. Even materials specifically made to cure more quickly might result in crystallization and cracking.
  • Consider using a primer before applying the adhesive when working with materials like nylon, acetal, and polyester to increase bond strength. 
  • Bonding PTFE? All PTFE and PTFE mixes must be ready with one side etched before the bonding may start with this material.


Frequently asked questions

Does bonding stick to plastic? Or Are all plastics bondable?

Due to their partial dissolvability, some plastics, such as various amorphous polymers, such as PC, PSU, PPSU, PES, PEI, PMMA, PS, and some PI, are simpler to bind.

Certain plastics, including ABS and acrylic, are simple to stick to one another using adhesives and solvent cement. Some materials, including HDPE and PP, are more challenging to bind.

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