Compatibilizers have proven effective in improving key properties such as the impact/stiffness balance of PCR and PIR blends of polyolefins and other plastics. #sustainable development
Recycled HDPE/PP sample without Dow Engage compatibilizer (top) and Recycled HDPE/PP sample with Engage POE compatibilizer. Compatibility tripled elongation at break from 130% to 450%. (Photo: Dow Chemical)
As plastics recycling becomes a growing market worldwide, compatible resins and additives are increasingly being used to solve hybrid resin problems in areas such as packaging and consumer products, construction, agriculture and automotive. Improving material performance, improving processing and reducing costs and environmental impact are among the key challenges, with mainstream consumer plastics such as polyolefins and PET leading the way.
A big barrier to using recycled materials is the costly and time-consuming separation of incompatible plastics. By allowing incompatible plastics to be melt-blended, compatibilizers help reduce the need for separation and enable material manufacturers to produce higher quality products, while at the same time increasing recycled content and accessing new low quality and low cost sources to lower costs.
These recyclable compatibilizers include specialty polyolefin elastomers, styrenic block copolymers, chemically modified polyolefins, and additives based on titanium aluminum chemistry. Other innovations have also appeared. All are expected to take center stage at upcoming trade shows.
According to Dow, Engage POE and Infuse OBC are best suited for HDPE, LDPE and LLDPE compatibility with polypropylene due to the PE backbone and alpha olefins as comonomers. (Photo: Dow Chemical)
Specialty polyolefin elastomers (POE) and polyolefin plastomers (POP), originally introduced to improve the properties of polyolefins such as impact and tensile strength, have evolved as compatibilizers for recycled PE and PP, sometimes also used with other materials such as PET or PET. nylon.
These products include Dow’s Engage POE, an OBC-infused ethylene-alpha-olefin comonomer random copolymer, a hard-soft block alternating olefin copolymer, and Exxon Mobil Vistamaxx Propylene-Ethylene and Exact Ethylene-Octene POP.
These products are sold to plastics recyclers/compounders and other recyclers, said Jesús Cortes, market developer at ExxonMobil Product Solutions, noting that compatibility can be a tool to help recyclers exploit cross-contamination and potentially low-cost key agents for polyolefin streams. Han Zhang, Director of Global Sustainability for Packaging and Specialty Plastics at The Dow Chemical Company, said: “Our customers benefit from creating a higher quality end product with access to a wider recycling stream. We serve processors who which use compatibilizers to increase recycled content while maintaining manufacturability.”
“Our customers benefit from creating a higher quality end product while having access to a wider recycling stream.”
ExxonMobil’ Cortés has confirmed that the same Vistamaxx and Exact grades suitable for virgin resin modification can also be used to ensure compatibility with recycled plastics. He noted that Vistamaxx polymers make HDPE, LDPE and LLDPE compatible with polypropylene, adding that due to the polarity of polymers such as PET or nylon, Vistamaxx grade grafting is required to make polyolefins compatible with such polymers. “For example, we have worked with several compounders to graft Vistamaxx to make polyolefins compatible with nylon while aiming to maintain the performance improvements that Vistamaxx polymers can bring to compound formulations.”
Rice. 1 MFR chart showing mixed colors of recycled HDPE and polypropylene with and without Vistamaxx additive. (Source: ExxonMobil)
Compatibility can be confirmed by improved mechanical properties, such as highly desirable impact resistance, according to Cortez. Increasing fluidity is also important when reusing materials. An example is the development of injection molding formulations for HDPE bottle streams. He notes that all the specialty elastomers available today have their uses. “The purpose of the discussion is not to compare their overall performance, but to choose the best tool for a particular project.”
For example, he said, “When PE is compatible with PP, we believe that Vistamaxx gives the best results. But the market also needs improved impact resistance, and ethylene-octene plastomers may be suitable when looking for low-temperature toughness.”
Cortez added, “Ethylene-octene plastomers like our Exact or Dow’s Engage grades and Vistamaxx have very similar load levels.”
Dow’s Zhang explained that while the presence of polypropylene in HDPE generally increases stiffness as measured by flexural modulus, it degrades properties as measured by toughness and tensile elongation due to the incompatibility of the two components. The use of compatibilizers in these HDPE/PP blends improves the stiffness/viscosity balance by reducing phase separation and improving interfacial adhesion.
Rice. 2. Impact strength graph showing different color blends of recycled HDPE and polypropylene, with and without Vistamaxx additive. (Source: ExxonMobil)
According to Zhang, Engage POE and Infuse OBC are best suited to make HDPE, LDPE and LLDPE compatible with polypropylene due to the PE backbone and alpha-olefin comonomer. As additives for PE/PP blends, they are typically used in amounts of 2% to 5% by weight. Zhang noted that by improving the balance of hardness and toughness, Engage POE compatibilizers such as Grade 8100 can provide more value for mechanically recycled PE/PP blends, including waste streams high in PE and PP. Applications include injection molded automotive parts, paint cans, trash cans, packaging boxes, pallets and outdoor furniture.
The market needs improved impact performance and ethylene octene plastomers can play a role when low temperature impact toughness is required.
He added: “The addition of only 3 wt. % Engage 8100 tripled the impact strength and tensile elongation of the incompatible HDPE/PP 70/30 blend while retaining the higher modulus imparted by the PP component,” he added, for the low temperature plasticity requirement, Engage POE provides impact strength at ambient temperature due to the extremely low glass transition temperature.
Speaking about the cost of these specialty elastomers, ExxonMobil’s Cortez said: “In the highly competitive recycling value chain, it’s important to balance cost and performance. With Vistamaxx polymers, the performance of recycled resins can be improved, allowing the resins to be used in applications where recyclers can gain higher economic value.” while meeting the demand for high performance materials.As a result, recyclers can have greater opportunities to market their recycled plastics, rather than just cost as the main driver, allowing them to focus on custom blends and throughput.”
“In addition to being able to recycle blended polyolefins, we are also working to promote the recycling of different blends such as polyolefins with engineering plastics such as nylon and polyester. We have provided a number of functional polymers, but new solutions are still in development. are being actively developed to address various plastic blends found in packaging, infrastructure, transportation and consumer applications.”
Styrene block copolymers and chemically modified polyolefins are other types of materials that have received attention as compatibilizers for reinforcing and improving the compatibility of recycled resins.
Kraton Polymers offers the CirKular+ styrenic block copolymer platform containing performance enhancing additives for plastics recycling and recycling. Julia Strin, director of global strategic marketing for Kraton Specialty Polymers, points to two series of five grades: the CirKular+ Compatibility Series (C1000, C1010, C1010) and the CirKular+ Performance Enhancement Series (C2000 and C3000). These additives are a range of block copolymers based on styrene and ethylene/butylene (SEBS). They have exceptional mechanical properties, including high impact strength at room or cryogenic temperature, flexibility to adapt stiffness and impact properties, improved resistance to stress cracking, and improved processability. Circular+ products also provide multi-resin compatibility for virgin plastic, PCR and PIR waste. Depending on the grade, they can be used in PP, HDPE, LDPE, LLDPE, LDPE, PS and HIPS, as well as polar resins such as EVOH, PVA and EVA.
“We have shown that it is possible to recycle polyolefin mixed plastic waste and recycle it into more valuable products.”
“CirKular+’s fully recyclable additives allow PCR to be reused by improving mechanical properties and supporting the design of polyolefin-based monomaterial products, thereby maximizing PCR content to over 90 percent,” said Stryn. unmodified resin. Testing has shown that CirKular+ products can be heat treated up to five times for more frequent use.”
The CirKular+ range of expanders are multi-resin expanders for upgrading mixed PCR and PIR recovery streams, typically added at 3% to 5%. Two examples of mixed waste recycling include an injection molded composite sample of 76%-PCR HDPE + 19%-PCR PET + 5% Kraton+ C1010 and a sample of 72%-PCR PP + 18%-PCR PET + 10% Kraton+ C1000. . In these examples, notched Izod impact strength was increased by 70% and 50%, respectively, and yield strength increased by 40% and 30%, while maintaining stiffness and improving processability. PCR LDPE-PET blends also showed similar performance. These products are also effective on nylon and ABS.
The CirKular+ Performance Enhancement Series is designed to upgrade cyclic mixed PCR and PIR streams of polyolefins and polystyrene at typical addition levels of 3% to 10%. Recent successful injection molding test: 91%-PCR PP + 9% Kraton+ C2000. The formulation has a 110% improvement in impact modulus balance over competing products. “High-end rPP applications in automotive and industrial applications require this kind of improvement. This could also be applied to packaging, but with less stringent requirements, the amount of C2000 will be reduced,” Streen said.
Kraton+ can be pre-blended or dry-blended with recycled plastic before molding, extrusion or as part of the recycling process, Stryn says. Since launching CirKular+ a few years ago, the company has achieved early adoption in areas such as industrial pallets, food and beverage packaging, automotive components and child car seats. CirKular+ can also be used in a variety of process applications including injection or compression molding, extrusion, rotational molding and compounding.
Polybond 3150/3002 is part of SI Group’s extensive range of Polybond chemically modified polyolefins and can be used as a binder and compatibility additive. It is a maleic anhydride grafted polypropylene that makes recycled polypropylene compatible with all types of nylon. According to John Yun, technical manager and technical support, at a typical usage level of 5%, it exhibits more than triple Izod notched impact strength and reverse Izod impact strength. Irfaan Foster, director of market development, notes that the initial application is car soundproofing. More recently, it has been used in recycled polypropylene and nylon blends for underfloor panels, underhood components, and behind dashboards.
Another grade is Polybond 3029, a maleic anhydride grafted high-density polyethylene introduced two years ago as an additive to improve the compatibility of wood-plastic composites. According to Yun, it looks like the company is on track to be compatible with a 50/50 PCR/pure HDPE blend.
Another class of compatibilizers is based on titanium-aluminum chemistry, such as the titanate (Ti) and zirconate (Zr) catalysts offered by Kenrich Petrochemicals and sold to compounders and moulders. The company’s products include a new catalyst in masterbatch or powder form that acts as a compatibility additive for a variety of polymers, including polyolefins, bioplastics such as PET, PVC and PLA. Its use in PCR blends such as PP/PET/PE is gaining momentum, according to Kenrich president and co-owner Sal Monte. This is reported to increase extrusion productivity and reduce injection molding cycle times.
Ken-React CAPS KPR 12/LV beads and Ken-React KPR 12/HV powder are reported to restore PCR to its original state. Monte said the product is the result of combining the company’s new LICA 12 alkoxy titanate catalyst with a mixed metal catalyst that is “more cost effective.” “We offer CAPS KPR 12/LV granules in quantities ranging from 1.5% to 1.75% of the total weight of all recycled materials added to the bin, just like masterbatch, and reduce the process temperature by 10-20%, to maintain the shear of the reaction mixture. They operate at the nanometer level, so a reactive shear of the composite is required, and the melt requires high torque.”
Monte says these additives are effective compatibilizers for additive polymers such as LLDPE and PP and polycondensates such as PET, organic and inorganic fillers, and bioplastics such as PLA. Typical results include a 9% reduction in extrusion, injection molding and blow molding temperatures and a 20% increase in processing speed for most unfilled thermoplastics. Similar results were obtained with a recycled 80/20% LDPE/PP blend. In one case, 1.5% CAPS KPR 12/LV was used to ensure the compatibility of three PIR resins: graduated fused film LLDPE, 20-35 MFI mixed injection molded polypropylene copolymer lids, and thermoformed PET food foldout packaging. Grind the PP/PET/PE mixture to 1/4″ size. up to ½ inch. Flakes and melts are mixed into injection molding pellets.
Interface Polymers’ patented diblock additive technology reportedly overcomes the inherent incompatibility of polyolefins at the molecular level, allowing them to be processed. (Photo: interfacial polymers)
Distribution business SACO AEI Polymers is the exclusive distributor of Fine-Blend in China, which produces a wide range of compatibilizers for polypropylene, nylon, PET, engineering thermoplastics and biopolymers such as PLA and PBAT, including recycled blends, additives and chain extenders. said business unit manager Mike McCormach. Auxiliary substances include non-reactive compatibilizers, mainly block and graft copolymers or random copolymers that do not participate in a chemical reaction when mixing polymers. BP-1310 is an example where addition levels of 3% to 5% improve the compatibility of recycled blends of polypropylene and polystyrene. An additive to improve the compatibility of recycled PE/PS blends is under development.
Fine-Blend reactive compatibilizers improve compatibility by chemically reacting with virgin polymer during blending, including ECO-112O for recycled PET, polycarbonate and nylon; HPC-2 for ABS and recycled PET compatibilizer; and SPG-02 for the production of polypropylene and recycled polypropylene. PET compatible. They contain epoxy groups that can react with recycled polyester’s hydroxyl groups to improve toughness and compatibility, McCormach said. There is also CMG9801, a maleic anhydride grafted polypropylene that can react with the amino groups of nylon.
Since 2016, the British company Interface Polymers Ltd. developed its proprietary Polarfin diblock copolymer additive technology, which reportedly overcomes the inherent molecular incompatibility of polyolefins, allowing them to be recycled. These diblock additives are suitable for virgin and recycled polyethylene and polypropylene compounds, sheets and films.
A major film manufacturer is working on a project to process multilayer films without significant loss of productivity. Business Development Director Simon Waddington said that even at low loading levels, Polarfin has eliminated gelling, a common problem hampering the recycling of polyolefin films using recycled blended plastics. “We have successfully demonstrated that polyolefin mixed plastic waste can be recycled and recycled into more valuable products using our Polarfin additive technology.”
According to ExxonMobil’s Cortes, compatibility (eg Vistamaxx with recycled PE/PP) can be demonstrated by improved mechanical properties such as impact resistance. (Photo: ExxonMobil)
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Post time: Jul-28-2023