Manufacturing process

Porous fiber uses heat and pressure in the bonding process similar to sintered porous plastics, but instead of bonding particles, it bonds fibrous strands.  A sheath is wrapped around customized fibers and the fibers are bonded in various configurations.  This does not involve knitting or weaving, but rather forming fibrous components including sheets, rods, tubes, blocks, and 3D geometrics.

Material options

The material used in bonded fibers is thoroughly evaluated based on product needs.  Here are the four main materials and some of their traits:

Polyolefins (LDPE, LLDPE, HDPE, PP)
This is the most commonly used material with the simplest molecular structure.  There are limitations on temperatures for many applications.

Polyesters (PET, PTT, PBT)
For versatility, and almost all fiber technology platforms

Polyamides (Nylon 6, Nylon 6,6)
For heat resistance and chemical compatibility.  Used in hydroscopic to hydrophilic applications.

Other Suitable Materials

• Cellulose acetate (CA) when you are wanting biodegradable materials
• Polylactic acid (PLA) which is a renewable raw material
• Polyphenylene Sulphide (PPS) for high temperature resistance applications
• Co-polymers in many configurations

While these are the most common materials used to design porous fiber components, there are many more that are possible and can be used based on your end product’s needs. Work closely with your application engineer to define your specifications, and they can help select the best material(s).

Physical properties

When designing a porous fiber component, it’s critical to understand three key physical properties desired as they impact the materials and functionality of the part: 

• Pore size: Pore size defines the size of the voids in the porous media. Depending on the material, pore size can be large or small, with faster flow control due to directional structure. We can control the diameter of the fibers and the density of the materials. This gives you greater control over wicking speed and distance, and filtration efficiency.
  
• Pore volume: Pore volume defines the percentage of air in the part compared with the total volume of the part. In porous fiber materials, density is more often used to define pore volume.  Density is inversely proportional to pore volume. This means that the heavier the part, the lower the pore volume. A higher pore density allows for greater absorption and flow resistance of liquid materials.  Porous fiber components have a wide range of capabilities including very low to high density.
  
• Operating temperature: Operating temperature defines the temperature range at which the final porous fiber part will be required to operate.
  

Understanding typical material properties will guide you in selecting the right polymer for your device’s function and operating conditions. The above characteristics can be highlighted or downplayed based on your specific product needs. Below is a chart that shows the common materials with their physical properties; however, this is not an exhaustive list. 

Chemical properties

Choosing the right polymer material is important to ensure lasting functionality for your end product or device.  One of the key questions to consider is with what – if any – chemicals the porous fiber component will come into contact. There are many types of porous polymers available to suit almost any operating environment or condition. 

Below is a table that shows chemical compatibility of the common polymers mentioned above:

Additive options

Additives and treatments open the door to many possibilities for your sintered plastic component. Below are some additives and treatments used with the common polymers listed above:   

Polyethylene (PE) and Polypropylene (PP) accept these options:

• Hydrophobic treatments
• Self-sealing, liquid barrier
• Hydrophilic treatments
• Colorants
• Color change
• Bactericidal / bacterial static
• Carbon, potable water, odor elimination
• Oleophobic treatment
• Laminated support structure

Geometric options

Porous fiber can be manufactured into a variety of shapes.  As you think about incorporating this material into your manufacturing process, consider these options:

• Sheets and Rolls
• Rods and Tubes
• 2D Plugs and Vents
• Nibs
• 3D Simple Structures  

Our engineers can also look at your manufacturing process and determine which size, shape and dimensions you need.

Assembly & converting options

Customizable assembly and converting options are endless. Typical options for porous fiber include:

• Thermal & ultrasonic welding
• Overmolding
• Die-cutting
• Press fit
• Pressure-sensitive adhesive (PSA)

It’s important to understand how the final product or device will be assembled when talking with our engineers, as sintered plastics can be used to decrease number of assembly steps by combining multiple parts into one custom-engineered part. 

How to use porous fiber

• Wick – Wicking works extremely well with porous fiber.  Porous fiber materials can be used in wicks for pregnancy tests or in inkjet printer cartridges.  The surface energy and adhesion properties of a particular bonded fiber material will determine how easy it is to wet-out.
  
  
• Filter – Oil filters for automobiles perform well with porous fiber filtration.  This leads to less frequent oil changes as a result of cleaner longer lasting oil.  Filters produced with bonded fibers are durable and long lasting.
  
  
• Diffuse – Diffusion is prevalent in our media and filters for single-use bioprocessing applications such as aquarium bubblers.  Porous fibers allow for complete customization and precise control over the diffusion rate.  The diffused amount increases over time.
  
  
• Apply – Application products such as whiteboard markers benefit greatly from porous fiber nibs.  The material allows the ink to apply evenly and completely onto a surface or substrate. 

This list of application examples are just a small selection of what is possible. Check out our market pages to see more examples of our porous polymers in action.