Plastics recycling is a key component of the current circular economy global theme that in turn is drawing strong attention to compatibilizers and additives used in advancing recycled plastics use. A perfect world where different types of plastics are separated into homogenous streams unfortunately does not exist.
Mixed streams will remain the norm. Novel compatibilizers will play a critical role in blending plastic recycle streams composed of commodity and engineering plastics, as well as combining virgin resins to recycle.
Equally important, performance additives for use in upcycling recycled plastics towards virgin polymer based propertied compounds remain under development.
Let’s start by looking at recycling compatibilizer advances followed by recycling additive options.
Recycling Compatibilizer Advances
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.
| Property |
Values
|
| Sample No. |
1 |
2 |
3 |
4 |
5 |
| No compatibilizer |
|
|
|
|
|
| SAG-001 |
|
0.3phr |
|
|
|
| SAG-001 |
|
|
0.5phr |
|
|
| SAG-005 |
|
|
|
0.5phr |
|
| SAM-002 |
|
|
|
|
0.5phr |
| Tensile strength |
56 |
57 |
57 |
58 |
58 |
| Flexural strength |
82 |
83 |
82 |
83 |
82 |
| Impact strength (1/8 ") |
514 |
582 |
602 |
628 |
594 |
| Impact strength (1/4 ") |
180 |
286 |
301 |
309 |
227 |
| Melt index |
29 |
24 |
24 |
23 |
25 |
| HDT |
118 |
121 |
121 |
122 |
120 |
Properties of 70/30 PC/ABS Blends Compounded with different Fine Blend compatibilizers
» Continue reading to learn more advances in recycling compatibilizers and additive options!