Properly addressing
the global issue of unsustainable plastic waste
generation and accumulation will require a confluence of technological
breakthroughs on various fronts. Mechanical recycling of plastic waste
into polymer blends is one method expected to contribute to a solution.
Due to phase separation of individual components, mechanical recycling
of mixed polymer waste streams generally results in an unsuitable
material with substantially reduced performance. However, when an
appropriately designed compatibilizer is used, the recycled blend
can have competitive properties to virgin materials. In its current
state, polymer blend compatibilization is usually not cost-effective
compared to traditional waste management, but further technical development
and optimization will be essential for driving future cost competitiveness.
Historically, effective compatibilizers have been diblock copolymers
or
in situ
generated graft copolymers, but recent
progress shows there is great potential for multiblock copolymer compatibilizers.
In this perspective, we lay out recent advances in synthesis and understanding
for two types of multiblock copolymers currently being developed as
blend compatibilizers: linear and graft. Importantly, studies of appropriately
designed copolymers have shown them to efficiently compatibilize model
binary blends at concentrations as low as ∼0.2 wt %. These
investigations pave the way for studies on more complex (ternary or
higher) mixed waste streams that will require novel compatibilizer
architectures. Given the progress outlined here, we believe that multiblock
copolymers offer a practical and promising solution to help close
the loop on plastic waste. While a complete discussion of the implementation
of this technology would entail infrastructural, policy, and social
developments, they are outside the scope of this perspective which
instead focuses on material design considerations and the technical
advancements of block copolymer compatibilizers.
Small-angle neutron scattering (SANS) is used to measure the conformation and solution thermodynamics of low dispersity, star branched poly(N-isopropylacrylamide) (PNI-PAM) in water using a newly developed form factor for starbranched polymers with excluded volume, in conjunction with the random phase approximation (RPA). Star PNIPAM is synthesized using both ATRP and RAFT, allowing the terminal group and number of arms to be precisely tuned from f = 3 to 6 arms, with bromine, phenyl, and dodecane terminal moieties. SANS measurements show that both the number of arms (f) and synthetic route (i.e., ATRP or RAFT) play a dominant role in the solution behavior of PNIPAM in relation to the interaction parameters, conformation of the arms of the polymer, and clustering/association of the polymers below the LCST. Dodecaneterminated PNIPAM polymers form small, sub-20 nm globules in solution, whereas phenyl-and bromine-terminated polymers form large, micrometer-scale clusters of nearly-Gaussian polymer chains. Multiangle light scattering (MALS) is used to probe the large clusters, finding that their size increases slightly with temperature but is largely independent of terminal group chemistry.
Poly(vinylidene fluoride-co-tetrafluoroethylene) (PVDF-TFE) is confined between alternating layers of poly(ethylene terephthalate) (PET) utilizing a unique multilayer processing technology, in which PVDF-TFE and PET are melt-processed in a continuous fashion. Postprocessing techniques including biaxial orientation and melt recrystallization were used to tune the crystal orientation of the PVDF-TFE layers, as well as achieve crystallinity in the PET layers through strain-induced crystallization and thermal annealing during the melt recrystallization step. A volume additive model was used to extract the effect of crystal orientation within the PVDF-TFE layers and revealed a significant enhancement in the modulus from 730 MPa in the as-extruded state (isotropic) to 840 MPa in the biaxially oriented state (on-edge) to 2230 MPa in the melt-recrystallized state (in-plane). Subsequently, in situ wide-angle X-ray scattering was used to observe the crystal structure evolution during uniaxial deformation in both the as-extruded and melt-recrystallized states. It is observed that the low-temperature ferroelectric PVDF-TFE crystal phase in the as-extruded state exhibits equatorial sharpening of the 110 and 200 crystal peaks during deformation, quantified using the Hermans orientation function, while in the melt-recrystallized state, an overall increase in the crystallinity occurs during deformation. Thus, we correlated the mechanical response (strain hardening) of the films to these respective evolved crystal structures and highlighted the ability to tailor mechanical response. With a better understanding of the structural evolution during deformation, it is possible to more fully characterize the structural response to handling during use of the high-barrier PVDF-TFE/PET multilayer films as commercial dielectrics and packaging materials.
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.