Stabilization and Processing of Recycled Plastics

The demand for recycled plastics continues to grow, driven by the global regulatory and environmental pressure on plastic waste and single-use plastics. 

Manufacturers and plastic end-users are creating sustainability stories and environmental initiatives to reduce plastic waste and the use of virgin resins and polymers. Across many industries, manufacturers and users of plastic materials are switching to recyclable plastic films and parts. This is occurring across several industries and end markets, including automotive, packaging, and consumer plastic products.

Environmental concerns with the plastic waste

Plastic-waste-recycling-plastic-materials.png
 

Why use recycled plastic?


Plastic waste and chemical pollutants are raising many environmental concerns and threats to aquatic life, wildlife, and humans. Sustainability is also one of the main drivers to increase the use of plastic recycling and decrease the use of non-recyclable plastic materials. Reducing plastic waste through recycling provides the following:
 

  • Lowers the waste sent to landfills

  • Reduces carbon footprint

  • Lowers energy needed to produce more plastics

  • Complies with the evolving environmental regulatory restrictions involving single-use plastics and plastic waste

  • Lowers the overall cost of plastics parts through the use of less expensive reused materials or by the utilization of plastic scrap back into production cycles

 
This pushes plastic compounders to develop their manufacturing processes and find solutions for the typical performance issues faced with the recycling and compounding of plastic materials. The main types of recycled materials are post-consumer and post-industrial plastic resins, depending on the source of the plastic waste and processability. This includes polyolefins, polyamides, PVC, PET, and various other thermoplastic materials.
 
A wide range of polymer additives is used in masterbatches and plastic recycling processes to enable the re-use of flexible and rigid plastics and to recycle scrap and waste produced from the plastic manufacturing processes.

Recycling Methods by Resin Type:

Before we get to the recycling and compounding solutions, let's explore the sources of plastic waste, recyclability, and common challenges faced by the plastic recycling industry:
 

1.  Post-Consumer Resins:

These are recyclable plastic materials that are sourced from consumer products waste, from carpeting waste to packaging plastics. PCR can be FDA compliant and commonly used on its own or in conjunction with virgin resins in various applications depending on the level of sorting and cleaning.

Common challenges faced with the processing of post-consumer plastics (PCR):

 

  • Compatibility:  

In recycling processing, multiple types of polymer types, fillers, and other ingredients are mixed in the production stream due to the application or sorting process. For that reason, compatibilization is a necessity for compounders to achieve the mechanical properties and desired specifications.
 

  • Impact strength, heat aging, gas-fading, and resistance to weatherability:

Since there is so much variability from lot to lot with the recycling of PCR base resin, a compounder must be able to respond instantly to the changing specs. Compounders must be able to respond to the changing specs by developing robust formulations that meet the broad specs of recycled plastic materials. This requires using a variety of plastic additives including, antioxidants, heat stabilizers, UV stabilizers, impact modifiers, processing aids, and more.
 
  • Melt stability: 

Maintaining the melt stability of recycled materials is more challenging than virgin polymers. Therefore, compounders optimize their processes and utilize additives to increase melt stability, reduce scrap, and limit plastic waste.
 

 2.  Post-Industrial Resins:

This type of recyclable material is made from recycling the scrap off production streams. PIRs are preferred over PCRs as they have a tighter spec range and are completely traceable; in other words, you know precisely the plastic types in the lot. However, this is still more challenging to process compared to virgin materials. Therefore, in-house recycling is also a way to control the specs by re-introducing scrap into production steams at a certain percentage of the formulation. Although recycling of post-industrial resins is more controlled, there are several challenges faced with the processing of PIRs:
 

  • Coloring: 

When trying to create specific colors or shades using recycled plastics, excluding black, color shifts are significant and difficult to control.
 

  • Deterioration of physical and mechanical properties:

Recycled industrial plastics have been through multiple heat cycles from the initial creation of the material, several production cycles, including extrusion and pelletizing, to the heat cycle for creating the new compound. Plastic additives, anti-oxidants, polymer modifiers, and chemical additives are used to improve stability throughout the recycling process. The recycling here will be an additional heat cycle that requires heat stability to prevent the deterioration of physical and mechanical properties in the produced plastic parts.
 

  • Other physical and mechanical properties:

Compounders face other challenges depending on the desired specs of the end-use application, including melt stability, gas fading, impact resistance, weatherability, stiffness, and mechanical strength.


 

Plastic Recycling Materials by Application:

Plastic additives for automotive plastics

Automotive


Examples: Automotive bumpers, roof racks, internal plastic parts, and lightweight accessories

Process types: Mostly injection molding

Plastic bottles and recycling of plastics

Plastic Packaging

 

Examples: Plastic containers, bottles, sheets, films, bags, cans, and other packaging materials

Process types: Extrusion, co-extrusion, blow molding, thermoforming, and calendaring

Consumer plastic bins and recycling of plastics

Consumer Products


Examples: sporting goods, appliances, flooring, carpeting, shoes, clothing, flowerpots, toys, and recycling bins

Process types: Injection molding, extrusion, and rotational molding

 

SI Group Recommended Solutions for Recycled Plastics:

 

Explore our recommended specialty polymer and plastic additives from SI Group for use in recycling streams and plastics. Find the suitable product by polymer or plastic-type and by application:

Polypropylene (PP):

 

  • Recycle stream types: PIR and PCR
  • Typical challenges/ problems solved: Compatibility, heat stability, melt stability, gas fading, color stability, and FDA clearance for specific applications

  • Applications: BOPP films, packaging, consumer products, non-structure automotive parts

  • Recommended solutions:

 

Polypropylene/ Nylon (PP/PA6):

 

  • Recycle stream types: PCR
  • Typical challenges/ problems solved: Compatibility, heat stability, melt stability, and impact resistance

  • Applications: Automotive parts, outdoor goods, and high resistance consumer products

  • Recommended solutions:

 

Polyamide or Nylon (PA6 and PA66):

 

  • ​Recycle stream types: PIR and PCR
  • Typical challenges/ problems solved: Compatibility, heat stability, melt stability, impact resistance, and weatherability

  • Applications: Automotive parts, outdoor and high resistance consumer products

  • Recommended solutions:

 

High-Density Polyethylene (HDPE):

 

  • ​Recycle stream types: PIR and PCR
  • Typical challenges/ problems solved: Compatibility, heat stability, melt stability, gas fading, color stability, plate-out, and FDA clearances

  • Applications: Packaging, pipes, and consumer products

  • Recommended solutions:

    • ANOX™ 20: Heat stability and weathering resistance additive

    • ANOX™ PP18: Heat stability and weathering resistance

    • ULTRANOX™ 626: Plastic gas fading and color stability

    • LOWINOX™ 1790: Plastic gas fading

    • ETHANOX™ 330: Heat stability, hydrolytic stability, migration, and FDA clearances for plastics

    • WESTON™ 705T: Melt stability, colorant stabilizer, hydrolytic stability, and reducing plate-out in plastics

    • POLYBOND™ PE coupling agents: Compatibility, retain critical mechanical properties, and compatibility with the use of filler materials and reinforcement fibers
       

Polyethylene Terephthalate (PET):

 

  • Recycle stream types: PIR and PCR
  • Typical challenges/ problems solved: Heat stability, molecular weight retention, GHS compliance, color stability, availability in liquid form, and FDA clearances

  • Applications: Packaging and POY filament for clothing, shoes, and furniture

  • Recommended solutions:

    • ULTRANOX™ 626: Color control, heat stability, molecular weight retention, FDA clearance, and low loading rate for packaging

    • WESTON™ 705T: Color control, heat stability, molecular weight retention, FDA clearance, and liquid form for POY filaments


Many other plastics additives are used to compound and reuse plastic polymers, such as plasticizers, internal lubricants, impact modifiers, flame retardants, anti-static additives, etc.

 

You can click below to explore our range of plastic additives from the SI Group. Find your solution by application and polymer type. Specialists are available for assistance and product recommendations.


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