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1. One-pot synthesis of robust silyl ether-based HDPE vitrimers with enhanced performance and recyclability

   https://doi.org/10.1016/j.polymer.2024.127374  

   Ash, Subhaprad; Sharma, Rishi; Shaker, Mohamed; Patil, Shalin; Cheng, Shiwang; Rabnawaz, Muhammad (August 2024, Polymer)

   Reported herein is a continuous one-step melt extrusion approach for highdensity polyethylene (HDPE) vitrimers. A grafting agent and a coagent were used to produce high-performing vitrimers. Maleic anhydride (MA) served as a reactive agent to facilitate crosslinking, while dimethyl maleate (DM) acted as a grafting enhancer by reducing the surface energy of HDPE grafted with MA. For comparison, MA alone was also tested as a grafting agent. The vitrimers obtained displayed superior mechanical properties compared with HDPE. The storage modulus, as well as crystallinity, were determined for the HDPE vitrimers. These vitrimers are reprocessable, thus supporting recycling efforts despite their crosslinked nature, owing to very fast relaxation due to low activation energy for the transesterification reaction. Consequently, these vitrimers are not only recyclable but also exhibit enhanced thermal and mechanical properties compared with conventional HDPE. 

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2. Continuous one-pot melt extrusion approach for high-density polyethylene-based vitrimers

   Rabnawaz, Muhammad (August 2023, ACS)

   In this presenation, I will discuss a continuous melt extrusion approach in one go for the synthesis of high-density polyethylene (HDPE)-based vitrimers. Vitrimers are produced with two grafting two agents, with maleic anhydride serving as a reactive agent to facilitate crosslinking while dimethyl maleate helped to lower the surface energy for better maleation. This improved property is reflected in the 2 wt% system, where the crosslinking density had doubled and enhanced the stiffness of the material. Overall, these vitrimers had enhanced tensile stress at break and impact resistance as compared to that of HDPE, while yet having a similar melting temperature and tensile stress at yield. The crystallinity of the polymers decreased and thus these materials may be strong candidates for 3D printing applications as they are less susceptible to the warping issues that are encountered with unmodifed HDPE. These vitrimers are reprocessable with torque pf ~ 30 Nm, and thus they can be readily recycled despite the crosslinking of layers which imparts them with better mechanical and thermal properties. 

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3. Effect of Filler–Polymer Interface on Elastic Properties of Polymer Nanocomposites: A Molecular Dynamics Study

   Chi Ma, 1 Tuo (September 2017, Tire science & technology)

   A coarse-grained model has been built to study the effect of the interfacial interaction between spherical filler particles and polymer on the mechanical properties of polymer nanocomposites. The polymer is modeled as bead-spring chains, and nano-fillers grafted with coupling agent are embedded into the polymer matrix. The potential parameters for polymer and filler are optimized to maximally match styrene-butadiene rubber reinforced with silica particles. The results indicated that, to play a noticeable role in mechanical reinforcement, a critical value exists for the grafting density of the filler–polymer coupling agent. After reaching the critical value, the increase of grafting density can substantially enhance mechanical properties. It is also observed that the increase of grafting density does not necessarily increase the amount of independent polymer chains connected to fillers. Instead, a significant amount of increased grafting sites serve to further strengthen already connected polymer and filler, indicating that mechanical reinforcement can occur through the locally strengthened confinement at the filler–polymer interface. These understandings based on microstructure visualization shed light on the development of new filler polymer interfaces with better mechanical properties. 

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4. Chemically Recyclable Linear and Branched Polyethylenes Synthesized from Stoichiometrically Self-Balanced Telechelic Polyethylenes

   https://doi.org/10.1021/jacs.3c12660  

   Jang, Yoon-Jung; Nguyen, Sam; Hillmyer, Marc A. (February 2024, Journal of the American Chemical Society)

   High-density polyethylene (HDPE) is a widely used commercial plastic due to its excellent mechanical properties, chemical resistance, and water vapor barrier properties. However, less than 10% of HDPE is mechanically recycled, and the chemical recycling of HDPE is challenging due to the inherent strength of the carbon–carbon backbone bonds. Here, we report chemically recyclable linear and branched HDPE with sparse backbone ester groups synthesized from the transesterification of telechelic polyethylene macromonomers. Stoichiometrically self-balanced telechelic polyethylenes underwent transesterification polymerization to produce the PE-ester samples with high number-average molar masses of up to 111 kg/mol. Moreover, the transesterification polymerization of the telechelic polyethylenes and the multifunctional diethyl 5-(hydroxymethyl)isophthalate generated branched PE-esters. Thermal and mechanical properties of the PE-esters were comparable to those of commercial HDPE and tunable through control of the ester content in the backbone. In addition, branched PE-esters showed higher levels of melt strain hardening compared with linear versions. The PE-ester was depolymerized into telechelic macromonomers through straightforward methanolysis, and the resulting macromonomers could be effectively repolymerized to generate a high molar mass recycled PE-ester sample. This is a new and promising method for synthesizing and recycling high-molar-mass linear and branched PE-esters, which are competitive with HDPE and have easily tailorable properties. 

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5. Functionalization of High‐Density Polyethylene Capillaries for Open Tubular Ion Chromatography

   https://doi.org/10.1002/jssc.202400455  

   Yousef, Enas; Shelor, Charles Phillip; Horn, Seth A; Dasgupta, Purnendu K (October 2024, Journal of Separation Science)

   ABSTRACT Ion chromatography is the anion analysis benchmark. A miniature form, Open Tubular Ion Chromatography (OTIC), has attractive attributes for efficient ion separations. Here, we fabricate and characterize high‐density polyethylene (HDPE) open tubular anion exchange columns (OTCs). We attach positively charged latex particles onto negatively charged capillary surfaces. For efficient OTIC, column diameters need to be < ∼20 µm; functionalizing the bore is challenging. Methods to introduce acid groups to an HDPE capillary bore, e.g., sulfonation using chlorosulfonic or sulfuric acid solutions, with or without grafting of an aromatic ring through photo‐ or chemical grafting first, are explored. Following quaternary ammonium latex attachment, the ion exchange capacity and separating abilities of each OTC were measured as an index of OTC performance. Gradual loss of capacity was observed for many of these; high‐resolution mass spectrometry confirmed the leaching of detached oxidized/sulfonated oligomeric fragments and consequent poisoning of the latex sites. Ways to ameliorate this and/or to rejuvenate the columns are also described. 

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