Latest Advances in Recycling Compatibilizers & Additive Options!

Fraunhofer's Compatibilization of Polyolefins with Block and Graft Copolymers
 

The plastics division at Germany's Fraunhofer LBF research institute is at the forefront of polymer blend compatibilization. Their polyolefin work with block and graft copolymers has focused on these type polymer system capabilities as compatibilizers for normally immiscible plastics. 

Copolyolefin compatibilizers work well with polar and non-polar blend segments. The goal is to improve mechanical strength by first preparing a polybutadiene block copolymer followed by hydrogenating it that translates into tailored compatibility for a given polyolefin in recycled and/or virgin resin form. The polyolefins used could be:
 

• High-Density PolyEthylene (HDPE)
• Low Density PolyEthylene (LDPE)
• Linear Low-Density PolyEthylene (LLDPE)
• PolyPropylene (PP), and
• PolyOlefin Elastomer (POE)

Styrene Ethylene Butylene Styrene (SEBS) blend with a variety of polyolefins that in turn compatibilize well with Styrene Ethylene Butadiene (SEB) di-block copolymers.
 

Fraunhofer's Compatibilization of PP/SEBS-Blend Using Tailored SEB-Diblock Copolymer

Fine-Blend Compatilizer Jiangsu's PC/ABS Compatibilizing Options for Recycled to Virgin Resins
 

China's Fine Blend Compatibilizer Jiangsu has developed PolyCarbonate (PC)/Acrylonitrile Butadiene Styrene (ABS) compatibilizing options for recycled to virgin resins. Two options came to the forefront namely, 70/% PC/30% ABS alloys with either:
 

• A styrene-acrylonitrile-maleic anhydride terpolymer (SAM-002) compatibilizer
• A styrene-acrylonitrile-glycidyl methacrylate (SAG) terpolymer with varying glycidyl methacrylate (GMA; SAG-001, SAG-005) compatibilizers, or

Compared to no compatibilizer 70/% PC/30% ABS alloys:
 

• Tensile strengths (MPa, Mega Pascals) were higher but relatively equal among the compatibilized options
• Impact strengths (J/m, Joules per meter) were also higher with more pronounced improvements for SAG versus SAM compatibilizer type
• SAG more so than SAM kinds had lower melt flows, and
• Improved Heat Defection Temperatures (HDTs) favored SAG use

In the following figures, Fine-Blend measured tensile and impact strength of PC/ABS blends compounded with different compatibilizers at 1/8-inch-thick plaque samples.
 

Tensile and Impact Strength of PC/ABS Blends Compounded with Different Compatibilizers
 

• Sample Number 1 - contains no compatibilizer
• Sample Number 2 - 0.3phr (per hundred parts, resin) SAG,001
• Sample Number 3 - 0.5phr SAG-001
• Sample Number 4 - 0.5phr SAG-005, and
• Sample Number 5 - 0.5phr SAM-002
   

In summary, SAG-modified PC/ABS alloys perform better than a SAM-modified system as a direct result of the terminal PC carboxyl group's strong reaction with the SAG's carboxylic group, which is the key to this strong compatibilizer option.

 

TCKT GmbH's Recyclable PP/PET Blend Film
 

Germany's TCKT GmbH has focused its developments efforts on making PolyPropylene (PP) and PolyEthylene Terephthalate (PET) films recyclable. In today's rapidly growing global food packaging market, both PP and PET find extensive use together in multilayer films. When these film types are coextruded and laminated together, a broad range of key food package properties become simultaneously available such as:
 

• Superior water and oxygen barrier
• Inline and cross web tensile strength or tenacity
• Ease of brand surface printability, and
• Food contact regulatory approval

Yet the great challenge with multilayer films is that the various layers are incompatible leading to near impossible recycling options. As a rule of thumb, when you remelt multilayer films their starting point plastic properties are reduced to the point where they are unusable in any new applications.

To overcome this obstacle, TCKT GmbH decided to find out how they could compatibilize a PP/PET film blend material that could also be recyclable. Next, they used a twin-screw extruder to compound a variety of formulations with and without a range of compatibilizers. This was followed by generating standardized molded test plaques for evaluating impact and tensile properties. They then rheologically characterized the various formulations via scanning electron micrography to draw conclusions on the various blend compositions correlations, morphology comparisons, and optimized mechanical properties.
 

TCKT GmbH's Scanning Electron Micrograph Showing a 75% PP/25% PET Blend
of an Injection Molded Specimen Morphology

Furthermore, TKCT GmbH looked at PP and PET degradation profiles, in terms of increased PET hydrolysis and PP oxidative weakness. Their research clearly identified that PP and PET can be successfully compatibilized by utilizing a maleic anhydride grafted PP. This grafting technique needs to be accompanied by consistent processing involving material pre-drying and vacuum degassing that is critical to reach ideal PP/PET film properties. New food grade packaging applications are under development by TKCT GmbH for their PP/PET blend material. 

 

Struktol®'s Viscosity Modifying & Recycling Additives

Let's begin with U.S. based Struktol®, a leading additives supplier. They focus on PolyPropylene (PP) recycling processing challenges from three perspectives namely:
 

• Melt Flow Rate (MFR)
• Odor minimization, and
• Homogenization

Their goal is to provide a range of viscosity modifiers that take low MFR recycled PP streams into higher MFR compounds, thus, enabling development opportunities in the broadest range of injection molding applications-eliminating low odor also helps in this regard. Being able to homogenize differing recycle streams gives the eventual compounder a level property and process balance from which to work forward.

Struktol®'s RP 23 has been developed as a PP viscosity modifying additive. It can be used at low 1% or lower loading levels by weight to significantly increase recycled PP stream MFRs. Similarly, their RP-53 additive reduces byproduct chemical odors. Equally important, TR 052 is their advanced homogenizing additive that acts as a melt blender for volume and engineered plastics. All these differentiated additive systems increase mechanical properties and improve processing of recycled PP streams used in compounding.

Additional Struktol® recycling additives are TR 229 targeted at:
 

• TR 229 - Targeted at PolyCarbonate (PC), PC/Acrylonitrile Butadiene Styrene (ABS), PolyAmide (PA, Nylon) 6, 66 that is US FDA (Food & Drug Administration) approved, and

• TR 219 - Aimed at PolyEthylene Terephthalate (PET) and PolyButylene Terephthalate (PBT)

These additive systems are most useful in lubricating and blending together contaminated recycle streams in the preceding polymer families. Contaminated PET waste streams with TR 219 homogenization effects under similar process conditions make excellent compound blends.
 

No Struktol® Blending Additive (L), Homogenized Additive Added (R)
 

Elsewhere in the Struktol® recycling additive product line, there is available:
 

• RP 38 at loading rates down to 0.2% by weight. It has been designed to blend recycled PP with large amounts of PolyEthylene (PE) contamination, while neutralizing odor, maintaining mechanical properties, and providing easy mold filling/release, and
• TR 251 with a combined surfactant/lubricant performance feature that can be used with a multiplicity of recycle streams with little MFR change and is particularly adaptable to easy part release in thin wall end use applications.
  
   

Imerys' Speciality Mineral-based Additives for Compatibilizing PP and HDPE
 

Let's turn our attention to a first ever 100% post-consumer recycled PP and High-Density PolyEthylene (HDPE) blend. It is used in commercially available consumer paint cans, injection molded by Great Britain's Emballator Packaging for Crown Paint. Imerys has developed a specialty mineral based additive technology that modifies the miscibility of the PP and HDPE phases and creates a network of bonds between them. Performance is superior to currently used olefin block copolymer compatibilizers.

It involves a mineral coating system useful in polyolefin compatibilization that has been patented. Their IM30 compound has very uniform mold shrinkage and strong color fastness consistency. Normally paint cans have not exceeded 30% recycle content in order maintain mechanical stiffness to impact properties to avoid product liquid content leakage. The IM30 compound is only available through Imerys Performance Additives' formulation service' It has achieved EuCertPlas sustainability in recycling certification.
 

100% Recycled PP/HDPE Imerys Compound Based Paint Cans
 

Imerys Performance Additives IM30 compound overcomes the historical difficulty in mixed polyolefin recycle streams that normally phase separate in successive plastic processing steps, further leading to poor mechanical property performance. Use of the Imerys coated mineral additive in IM30 compounds saves on the expensive sorting part of the recycling chain and increases recycling rates.

Additionally, the IM30 recycled PP/HDPE compound has mechanical properties similar to virgin PP and HDPE. It can replace virgin PP or HDPE at a cost saving, reduces overall scrap rates, and works reliably in high performance polyolefin applications.

 

Vertellus' ZeMac® Extend P for Recycled PET
 

Finally, Vertellus' ZeMac® Extend P chain extender additive type is used to improve recycled PolyEthylene Terephthalate (PET) and is potentially applicable to related polyester material variants, including virgin resin equivalent materials. This specialty additive increases recycled PET molecular weight and ultimately melt viscosity. Other key performance benefits are low extrudate sag leading to faster processing rates particularly in extruded applications, improved impact strength, and neutralization of hydrolytic degradation. 

ZeMac® Extend P modified recycled PET achieves near virgin PET resin properties and enhances sustainability where these compounds can absorb low cost waste streams. Process related applications include injection molding; film, sheet, tape and profile extrusion; bottle extrusion blow molding; and strapping and foamed sheet extrusion. 

A related patent pending development is their Link NP alloying additive. It is targeted at compatibilization improvement for engineered plastic applications such as office furniture, nuts and bolts fasteners, hand tools, small appliances, outdoor power equipment, and auto wheel covers. Glass fiber, mineral fillers, and impact modifiers can be easily incorporated into this alloy option to maximize cost efficiency.
 

Vertellus ZeMac® Link NP Enhanced Recycled PET/Nylon Alloy 
Increases Drill Housing Electrical Insulating Properties