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The unprecedented growth and socioeconomic impacts of polyolefins clearly outline a major success story in the world of polymer science. Polyolefins revolutionizes industries such as health care, construction, and food packaging. Despite the benefits of polyolefins, there is a rising concern for the environment due to high production volume (i.e., fossil fuel consumption), often short usage time, and problems related to waste management and accumulation in the natural environment. Creating a circular economy for polyolefins through effective recycling technologies has the potential to decrease the environmental impact of these materials. This perspective discusses polyolefins and their impact, existing and emerging recycling/upcycling solutions, and recycle‐by‐design alternatives that are challenging the status quo. [ABSTRACT FROM AUTHOR]

Maleic anhydride‐grafted‐polyethylene was dynamically cross‐linked via reactive melt blending with 4,4′‐dithiodianiline. Thermal and mechanical properties of polyethylene vitrimers with different cross‐linking density were investigated. The results indicate that the degree of crystallinity decreased with increasing cross‐linking density. This behavior was directly related to short‐term and long‐term mechanical properties: vitrimers showed a decrease in yield strength and creep performance. The yield strength of PE vitrimers decreased linearly in relation to the degree of crystallinity. Polarized optical microscopy revealed that the cross‐links inhibit the growth of spherulites structure in polyethylene vitrimers. Thermogravimetric analysis indicated an increase in the onset degradation temperature and decomposition rate for vitrimers with increased cross‐linking density. The stiffness of the vitrimers decreased with increasing cross‐linking density which led to higher damping properties. Finally, it was demonstrated that reprocessing of polyethylene vitrimer was possible without significant impact in mechanical properties. [ABSTRACT FROM AUTHOR]

Polyolefins have traditionally been polymerized via the heterogeneous Ziegler Natta (Z‐N) catalysts since their discovery in the 1950s, but the later developments of the homogeneous single site metallocene/methylaluminoxane (MAO) catalysts have opened the possibility for the synthesis of polyolefin polymers and copolymers (commercialized in the 1990s) with highly defined microstructure and great degree of control of their molecular architecture resulting in some unique beneficial properties compared to their Z‐N counterparts. The main aim of the work reported here was to examine critically the effects of the processing conditions during multipass extrusions on the molecular and rheological characteristics of metallocene‐catalyzed linear low density polyethylene and a Ziegler‐Natta‐based counterpart polymer and on the thermoxidative (in the melt) stability of their melts and their stabilization. Both polymers examined here were based on ethylene‐1‐hexene copolymers and produced by the same manufacturer with similar density and melt index (MI) values. The melt stability and rheological properties of the polymers were determined from melt flow and capillary rheometric measurements. The molecular characteristics were investigated using GPC for molecular weight determination, 13C‐NMR for short chain branching, 1H‐NMR and FTIR for the type and concentration of unsaturation groups, FTIR for carbonyl‐containing compounds and chemical analysis for hydroperoxide determination. The processibility of the two polymers was compared through examination of different processing conditions (die temperatures 210–285°C, screw speeds 50–200 rpm) used for a multipass extrusion process. Further, the effects of the processing conditions on the melt thermoxidation of the differently catalyzed LLDPE polymers were investigated. The results demonstrated that both the catalyst type and the processing conditions have a great effect on both the rheological and the themoxidative behavior of the polymers as well as on the balance between the competing oxidative reactions taking place in the polymer melt, for example, chain scission and crosslinking reactions. The results obtained for the different multipass extrusion conditions of the two polymers have illustrated clearly that the degradation mechanisms during their melt processing are substantially different. The melt degradation route of the Ziegler‐catalyzed polymer was shown to be dominated by chain scission reactions under all the processing conditions examined, and more so at the higher shear rates and temperatures. By contrast, the evidence clearly showed that the metallocene‐catalyzed polymer gave rise to crosslinking reactions that predominated even under the more severe processing conditions, that is, higher temperatures and shear rates. [ABSTRACT FROM AUTHOR]

A series of high‐density polyethylene (HDPE) – chitosan (CS) composites with varying concentrations of chitosan have been prepared using a peroxide‐initiated melt mixing process with maleic anhydride as compatibilizer. Palm oil has been added as a plasticizer to the optimized HDPE/CS5 composite. The variation in the free hole volume, microstructure, and crystallinity of the prepared composites has been studied using Positron annihilation lifetime spectroscopy (PALS), dynamic mechanical analysis (DMA), and X‐ray diffractometry (XRD) respectively. The interaction between HDPE and chitosan is evidenced from the FTIR spectroscopic studies. The addition of palm oil to optimized HDPE‐CS composite increased the crystallinity upto 41.3%. A shift as well as a decrease in loss modulus was obtained for 5 wt% chitosan added HDPE sample which can be ascribed to the better crosslinking observed in the composite. The increased amorphization of HDPE‐chitosan composites with a higher concentration of chitosan beyond the optimized concentration is observed from the tan delta values. Free‐hole value is reduced by 20 Å3 with the addition of 5 wt% palm oil to HDPE/CS5 composite system. The microstructural analysis shows evidence of efficient interaction of HDPE‐chitosan system that can be used for further applications in medical field and food packaging industry. [ABSTRACT FROM AUTHOR]

Along the Costa Rican Caribbean shoreline, it is possible to find two species of crocodilians, the American crocodile (Crocodylus acutus) and the spectacled caiman (Caiman crocodilus). This region can be divided geographically into three subregions: North, Central, and South Caribbean. We conducted this research in the North Caribbean, between October 6, 2018 and August 31, 2019. Specifically, we worked in the area lying between the Jalova Station of the Tortugero National Park (TNP) and Agua Dulce Lake situated in the northern tip of Machuca Island, at the mouth of the Colorado River inside the Barra del Colorado National Wildlife Refuge (BACORE), which includes other connecting wetlands as well (Sierpe River, Samay Lake). Overall, this study area had an approximate extension of 408 km² characterized by large, wide and deep canals, as well as wetlands, meanders, and adjacent lakes. The sampling was performed along 10 segments that varied in length from 7.5 km up to 29.49 km, located in the nearby zones of TNP and BACORE. In these zones, nightly counts were carried out using dazzling lamps. Individuals of C. acutus and C. crocodilus were classified into eight and six body size classes, respectively (both with 50 cm intervals). A relative abundance of 0.55 crocodiles and 1.37 caimans per linear kilometer was estimated during these spotlight surveys. The capture of 39 caimans let us to estimate a ratio of 30 males to 9 females (3.3:1 M:F). In stark contrast, only 1 male and 1 female crocodile were captured. A total of 85 C. acutus and 205 C. crocodilus were observed. Regarding the number of caiman sightings in the TNP, a statistically significant difference was found (X²=5.62, p≤0.05) for the distribution by sizes between the zones of BACORE and TNP, whereas no such difference was found for C. crocodilus sightings (Z=-1.22, p≥0.222). Some segments had a higher probability of caiman occurrence than did others in the surveys performed during the monitoring period (X²=8.36, p≤0.05), especially the Jalova-Sierpe River, Caño Negro-Tortuguero, and Tortuguero-Samay Lake (Tortuguero subarea) segments. Ninety percent of the sightings occurred in the BACORE zone, and this was significantly different (X²=7.34, p≤0.026) from the studied subareas. The number of crocodile sightings in the Colorado River segment was significantly different and higher than the other segments (X²=7.28, p≤0.05). There was a significant statistical difference among the sizes in all areas of study (X²=5.529, p≤0.026). The abundance of C. acutus and C. crocodilus in the north Caribbean part is lower than in the central Caribbean part of Costa Rica, where this species could use the resources available in more urbanized areas. [ABSTRACT FROM AUTHOR]

Milled sunflower husk was added to three types of polyolefins (polypropylene, low‐density and high‐density polyethylene) in a wide composition range. Composite series were prepared with or without maleic anhydride‐grafted polyolefin coupling agents to investigate the effect of coupling on the mechanical properties and micromechanical deformation processes. Several independent approaches were followed to estimate interfacial adhesion qualitatively and quantitatively, respectively. The results show that interfacial adhesion is significantly improved in the presence of a coupling agent. As a result, coupling changes the dominant deformation process from matrix/filler debonding to the fracture of sunflower husk particles. Milled sunflower husk can enhance significantly the modulus of polyolefins; however, elongation‐at‐break values are very small, especially at larger filler content, which represents the largest obstacle of practical application. [ABSTRACT FROM AUTHOR]

Polyisobutylene (PIB) bearing covalently bound antioxidants is reported. TiCl4‐catalyzed cleavage/alkylation reactions were conducted on poly(isobutylene‐co‐isoprene) (EXXON® Butyl 068; M¯n = 3.37 × 105 g/mol, (Ð) = 1.29, and 1.08 mol % isoprene) at −70 °C in 60/40 hexane/dichloromethane in the presence of 2,6‐di‐tert‐butylphenol (DTP). Resulting PIB M¯n s ranged from 30,000 to 85,300 g/mol and number average DTP functionalities (Fn) ranged from 4.3 to 12.0. 1H NMR showed that 25%–40% of the DTP moieties underwent de‐tert‐butylation to form mono‐tert‐butyl phenol moieties. DTP‐functionalized and nonfunctionalized control PIBs were subjected to thermogravimetric analysis in nitrogen and in air. In nitrogen, commercial control PIBs (olefinic end groups) showed delayed onset of thermal degradation (T10 = 380–381 °C) relative to both control PIBs produced by living polymerization (tert‐chloride end groups) and DTP‐functionalized PIBs (T10's all within the range of 366–370 °C). All PIBs showed lower degradation temperatures in air compared to nitrogen. Various control PIBs suffered 90% weight loss in air at temperatures ranging from 372 °C to 410 °C; DTP‐functionalized PIBs did not suffer 90% weight loss in air until 412–414 °C. Oxidative induction time analysis showed that all control PIBs suffered catastrophic degradation within 6 min, and most within 1 min, but DTP‐functionalized PIBs resisted degradation for >100 min. © 2019 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2019, 57, 1836–1846 [ABSTRACT FROM AUTHOR]

Fused deposition modeling (FDM) is one of the trendiest three-dimensional printing (3DP) technologies. However, FDM products based on virgin polyamide-6 (PA6) are seriously warped due to the accumulation of shrinkage stress generated from the crystallization of PA6. To solve this problem, maleic anhydride grafted poly(ethylene 1-octene) (POE-g-MAH) is added into PA6 to disturb the crystallization and reduce the shrinkage stress. Besides, rigid polystyrene (PS) with good flowability is further introduced to PA6/POE-g-MAH blend because too much addition of POE-g-MAH will weaken the PA6/POE-g-MAH, which will interrupt the printing process. The POE-g-MAH and PS both act as amorphous phase in the blends, which will reduce the shrinkage stress and is helpful to the shape stability of the printed products. Finally, a new kind of PA6-based filament with good toughness for FDM is prepared via this facile method. POLYM. ENG. SCI., 57:1322-1328, 2017. © 2017 Society of Plastics Engineers [ABSTRACT FROM AUTHOR]

HDPE/CaCO/LDPE-g-MA composites of high density polyethylene (HDPE) and calcium carbonate (CaCO) with maleic anhydride grafted low density polyethylene (LDPE-g-MA) as a compatibilizer were prepared by melt mixing. LDPE-g-MA was prepared using a solution process. The maximum grafting degree was obtained at 6 wt% maleic anhydride (MA) and 0.2 wt% dicumyl peroxide (DCP) at 120 °C and 240 min. Functional groups not found in pure LDPE were observed with the formation of LDPE-g-MA. The successful dispersion of CaCO particles in the HDPE matrix using LDPE-g-MA was revealed. The crystallite size of the composites was a little higher than that of CaCO. The mechanical properties of the HDPE/CaCO/LDPE-g-MA composites increased with decreasing CaCO content. Thermogravimetric analysis (TGA) revealed a higher thermal stability for the HDPE/CaCO/LDPE-g-MA composites than for pure HDPE. Differential scanning calorimetry (DSC) revealed that the crystallization conditions were not substantially different. However, melting enthalpy and crystallinity increased with decreasing CaCO content. The thermal stability was greatly improved compared to that previously reported for nano CaCO. [ABSTRACT FROM AUTHOR]