Polyolefin Elastomer Research Articles

Development of energy-efficient synthesis/separation process for polyolefin elastomers using improved meta-heuristic techniques

The objective of this research is to develop an energy-efficient and sustainable synthesis/separation process for the production of polyolefin elastomers, as well as identify the optimal operating conditions for this process. The proposed approach involves integrating additional reactors into the existing reactor network and implementing energy-saving strategies into the distillation process. To optimize the operating conditions, we employed three different meta-heuristic optimization techniques: non-dominated sorting genetic algorithm Ⅱ (NSGA-Ⅱ), multi-objective particle swarm optimization, and multi-objective grey wolf optimizer. These techniques are utilized to simultaneously minimize total annualized cost (TAC), CO2 emissions, and condition number. To enhance the efficiency of these algorithms, we introduced the population distribution factor as a metric to enhance computational efficiency without compromising problem-solving aptitude. The results demonstrate that the improved algorithms offer enhanced computational efficiency and remarkable problem-solving ability and that NSGA-II outperforms the other algorithms in practical engineering problems. The proposed synthesis/separation sequences can reduce TAC and CO2 emissions simultaneously, while maintaining good controllability.

Flexible strain sensors with high sensitivity and large monitoring range prepared by biaxially stretching conductive polymer composites with a bilayer structure

AbstractIn order to prepare a flexible strain sensor with a large monitoring range, high sensitivity and excellent stability, a polyolefin elastomer (POE)/carbon nanotubes (CNTs) conductive polymer composite with a bilayer structure was prepared by biaxially stretching in this work. The results showed that the bilayer structured nanocomposites had better processability and better stability than monolayer CNT/POE nanocomposites during biaxial stretching. The biaxial stretching process could promote the dispersion and planar orientation of CNTs within the polymer, improving the crystallinity of nanocomposites and the sensing performance of strain sensors. The optimal stretching ratios (SRs) of bilayer structured nanocomposites were studied. The 8 wt% CNT/POE‐POE strain sensor with an SR of 2.5 exhibited a high sensitivity (gauge factor/GF = 72604.7 at 900% strain), wide strain range (0%–900%), and stable cycling performance (1000 cycles at 30% strain), showing a broad application prospect in wearable electronic devices. This study provides a valuable method for efficiently manufacturing high performance and low‐cost flexible strain sensors.

Flow-induced alignment of titanium dioxide nanorods in polyolefin tubes for use in catheters

Interventional catheters are the pivotal components of catheter-assisted intervention therapy. However, the inevitable contact and friction between catheters and complex human channels usually lead to severe patient burdens. A fabrication strategy for variable-stiffness catheters based on time-dependent helical flow was developed by regulating the alignment of titanium dioxide (TiO2) nanorods in polyolefin elastomer (POE) catheters. In particular, the uniaxial and off-axial alignments of the TiO2 nanorods were manipulated to adjust the mechanical properties of each section in the POE catheters, where the processing flow pattern was transformed from axial to helical. To achieve the desired performance in practical applications, two catheters with a programmable helix angle of embedded TiO2 nanorods along the axial direction were designed. Correspondingly, the as-designed catheters displayed remarkably reduced interventional loads (e.g., a maximum reduction of 49.3% and 39.7% in single- and multi-curvature channels, respectively) and an enhancement of 50% in rotation synchronization, indicating promising potential for application in catheter-assisted interventional therapy. This study proposes an effective structuring design strategy for composed catheters with variable-stiffness segments that can be extended to all interventional catheter production techniques.

Development of Unstable Flow and Morphological Analysis of Flow Marks in Injection Molding of Polypropylene and Polyolefin Elastomer Blend

Development of Unstable Flow and Morphological Analysis of Flow Marks in Injection Molding of Polypropylene and Polyolefin Elastomer Blend

Stable passivation of cut edges in encapsulated n-type silicon solar cells using Nafion polymer

In this study, the edge passivation effectiveness and long-term stability of Nafion polymer in n-type interdigitated back contact (IBC) solar cells are investigated. For new module technologies such as half-cut, triple-cut, or shingled modules, cutting of the cells introduces unpassivated edges with a high recombination rate and this limits the module power. These cut edges can be “repassivated” after cutting and in this work Nafion polymer is used to achieve this. First, different edge types, namely emitter edges (n+/n/p+) and back surface field (BSF) edges (n+/n/n+), as well as different cutting techniques such as laser cut and cleave (L&C), thermal laser separation (TLS), and mechanical cleaving are evaluated. It is found that TLS and mechanical cleaving enable good repassivation on both BSF and emitter edges. Second, industrial-size IBC solar cells are made to assess the effect of the edge repassivation on performance. On 1/4-cut M2 size IBC cells with two emitter edges, efficiency is improved by over 0.3%abs. However, an efficiency improvement was not observed for similar cells with BSF edges, due to an insufficient passivation at the bulk edges. Last, the real-world stability of the Nafion repassivation is evaluated in industrially relevant module stacks by laminating the repassivated wafers with ethylvinylacetate (EVA) or polyolefin elastomer (POE) encapsulants and then exposing them to industry standard testing of 1000 h under damp heat conditions (85 °C, 85% relative humidity). The tests reveal that the repassivation is stable in EVA encapsulants but not in POE.

Development of packaging based on PLA/POE/SeNPs nanocomposites by blown film extrusion method: Physicochemical, structural, morphological and antioxidant properties

The aim of the current study was to prepare a novel and biodegradable polylactic acid (PLA) film by the addition of different concentrations of polyolefin elastomer (POE; 10, 20 and 30 wt%), selenium nanoparticles (SeNPs; 1.5 wt%) and triethyl citrate (TEC) as plasticizer in order to modify physical and mechanical properties of the film. The SeNP with mean particle diameter of 170 nm was successfully prepared by using ascorbic acid and polyvinyl alcohol as the reducing and binding agent. The FT-IR results showed new chemical interactions among PLA matrix and incorporated POE and SeNPs. Tensile strength and Young’s Modulus of the nanocomposite films decreased by adding SeNPs and POE, whereas the elongation at break of the films significantly increased (p < 0.05). DSC analysis indicated that the crystallinity and melting temperature of PLA matrix were reduced by incorporation of SeNPs and POE. Swelling of nanocomposite films were significantly higher than that of neat PLA (p < 0.05). Adding SeNPs and POE, caused a notable reduction in water vapor permeability (WVP) of nanocomposite films (by 77% in the sample with 20% POE). Scanning electron microscopy (SEM) images confirmed the homogenous, uniform, and compact structure of the nanocomposites at 10% POE. Moreover, the anti-oxidant activity increased significantly with the incorporation of POE. Overall, the developed PLA/POE/SeNPs composite films can potentially be used for food packaging with enhanced barrier and mechanical properties.

One-step reactive processing of vitrimeric thermoplastic polyolefin elastomer with greatly improved thermo-mechanical property

Chemically crosslinking can enhance mechanical strength, dimensional stability and heat-resistance of thermoplastic polyolefin elastomers. However, chemically crosslinked elastomers suffer from reduction of flowability and strong shrinkage after reprocessing. In this work, inspired by vitrimer concept, olefin block copolymer (OBC) elastomer was chemically modified with dynamic boronic ester bond through one-step reactive processing. Based on the swelling test, FT-IR sperctra and DMA investigation, OBC vitrimer with tunable composition of dynamic Boron–Oxygen(B–O) bonds has been successfully prepared. Based on classical Arrhenius theory, the calculated activation energy (Ea) of OBC vitrimers ranges from 7.838 kJ/mol to 46.851 kJ/mol due to combined effect of chemical and dyanmic crosslinks. The prepared OBC vitrimers shows good creep-resistance, great reprocessability and good mechanical properties including tensile strength up to 15 MPa, elongation at break of 2300%, and elastic recovery of 90% at 300% strain. Interestingly, OBC vitrimers show significantly improved high-temperature mechancial property, i.e., tensile strength of ∼0.12 MPa and elongation excess 1200% at 120 °C where both OBC and OBC-DCP samples break instantly. Therefore, our work shows a promising industrial-scale strategy to prepare vitrimer elastomers via reactive processing, and provides guidance for molecular design of high-performance vitrimeric polyolefin elastomers.

Pyrolysis behavior of automotive polypropylene plastics: ReaxFF molecular dynamics study on the co-pyrolysis of polypropylene and EPDM/POE

The pyrolysis mechanism of automotive polypropylene (PP) plastics is essential for their recycling. Ethylene-propylene-diene monomer (EPDM) rubber and polyolefin elastomers (POE) are two common additives used in automotive polypropylene plastics, but little is known about the influence of the above two on PP pyrolysis. In this work, the molecular models of EPDM and POE were constructed. Then the pyrolysis behaviors of PP, EPDM, and POE were investigated by reactive force field molecular dynamics (ReaxFF MD), and also the co-pyrolysis of PP and EPDM/POE. The results showed that the content of C40+ products decreased rapidly and the other components were formed in 300–400 ps (2000–2500 K) in all the systems. The co-pyrolysis of PP and EPDM promoted the formation of the tar and delayed the formation of C40+ products. While the co-pyrolysis of PP and POE increased the gas formation, especially C2H2 and C3H4, but inhibited the formation of heavier components. It was also found that C2H2 was mainly from C2H3, C3H5, and C5H6, and C3H4 was mainly from C3H3, C3H5, C4H7, C6H8, and C6H9. The contents of C2H3, C3H3 and C3H5 were significantly high in the PP-POE system. Finally, the associated radical reactions were observed in the overall reaction pathways.

Investigation of the Effect of Hybrid Nanofiller on the Mechanical Performance and Surface Properties of Bio-Based Polylactic Acid/Polyolefin Elastomer (PLA/POE) Blend.

Polylactic acid has stood out among bio-based polymers for its usage in the food packaging industry and biomedical fields. Through the melt mixing process, the toughened poly(lactic) acid (PLA) was prepared with polyolefin elastomer (POE), incorporated via various ratios of nanoclay and a fixed amount of nanosilver particles (AgNPs). The correlation between the compatibility and morphology, mechanical properties, and surface roughness of samples with nanoclay was studied. The calculated surface tension and melt rheology confirmed the interfacial interaction demonstrated by droplet size, impact strength, and elongation at break. Each blend sample exhibited matrix-dispersed droplets, and the size of POE droplets steadily dropped with increasing nanoclay content, corresponding to the enhanced thermodynamic affinity between PLA and POE. Scanning electron microscopy (SEM) acknowledged that the inclusion of nanoclay in the PLA/POE blend ameliorated the mechanical performance by preferable localization in the interface of used components. The optimum value of elongation at break was acquired at about 32.44%, where the incorporation of 1 wt.% nanoclay led, respectively, to 171.4% and 24% enhancement rather than the PLA/POE blend with the composition of 80/20 and the virgin PLA. Similarly, the impact strength reached 3.46 ± 0.18 kJ m-1 as the highest obtained amount, showing the proximity of 23% progress to the unfilled PLA/POE blend. Surface analysis indicated that adding nanoclay caused the augment of surface roughness from 23.78 ± 5.80 µm in the unfilled PLA/POE blend to 57.65 ± 18.2 µm in PLA/POE contained 3 wt.% nanoclay. Rheological measurements implied that organoclay resulted in the strengthening of melt viscosity as well as the rheological parameters such as storage modulus and loss modulus. Han plot further showed that the storage modulus is always higher than the loss modulus in all prepared PLA/POE nanocomposite samples, corresponding to the restriction of polymer chains mobility induced by the formation of strong molecular interaction between nanofillers and polymer chains.

Study of Mechanical, Thermal, and Microstructural Properties of Polypropylene/Ceramic Waste Composites

In this work, the effect of reinforcement of the iPP with ceramic waste (CW), and the use of maleic anhydride compatibilizing agent grafted with polyolefin elastomer (POE-g-MAH) are studied. The composites were fabricated by extrusion and injection processes, and their morphology and microstructure, as well as fracture surface and mechanical and thermal properties were analyzed. Characterization by polarized optical microscopy showed that the ceramic waste particles were well-dispersed into the iPP matrix without the presence of agglomerates. However, the POE-g-MAH did not show good compatibility when it was added to the iPP/CW composite. Hardness Rockwell R, tensile and flexural measurements showed that the hardness, Young´s modulus, and flexural modulus increased with the incorporation of CW and without the POE-g-MAH. The ductility of the composites was several decreased with the addition of CW. POE-g-MAH affected the hardness, ductility, strength tensile, Young´s modulus, flexural modulus, and interfacial interaction in the iPP/CW composite. Analysis by X-ray diffraction showed that the CW also acted as a nucleating agent, increasing the crystallization degree, and forming the β-phase. Analysis of the Fourier transformed infrared showed transmittance bands of the iPP, CW, POE-g-MAH and composites. The bands were similar and there were no major changes in characteristic bands of composites, but CW and POE-g-MAH produced changes in the shape and intensity of band peaks of the iPP matrix. The CW addition to the iPP matrix modified the thermal properties of pure iPP, such as the degree of crystallization and melting temperature in the iPP/CW composites. The incorporation of POE-g-MAH decreased the crystallization temperature and crystallinity degree in the iPP/CW composite.

Low-voltage triggered electroactive and heat-responsive thermoplastic elastomer/carbon nanotube polymer blend composites

This study presents the synthesis and characterization of novel polymer composites that are triggered by heat and electricity. The composites were made of a blend of a styrenic block copolymer and a thermoplastic polyolefin elastomer, with multi-walled carbon nanotubes (MWCNTs) added as fillers. The composites were prepared through melt blending and the amount of MWCNTs was varied from 1 to 10 phr. The results of morphological characterization showed that the distribution of fillers within the matrix improved as the amount of MWCNTs increased. The crystallization temperature was also found to decrease due to the nucleation effect of the fillers. The reinforcing effect of MWCNTs resulted in increased values of elastic modulus, creep resistance, and storage modulus, while decreasing the values of elongation at break, creep recovery, and damping parameter (tanδ). The electrical resistance of the composites decreased with increasing amounts of MWCNTs, with the lowest resistance recorded in the composite which contains 10 phr MWCNT (10CNT) composite at 12 ohm.cm. The 10CNT composite was also able to be heated up to 75 °C by Joule heating at a voltage of 5.5 V. The shape fixing performance of the blend improved in the presence of fillers, however, despite an increase in the recovery stress value, the heat-responsive shape recovery feature worsened. The composite having 5 phr MWCNT (5CNT) showed electro-active shape recovery under 25 V in 210 s, while the 10CNT composite completed this process in 300 s under 5.5 V. The results of this study demonstrate the potential of using MWCNTs as fillers in polymer composites for various applications that require both electrical conductivity and heat responsiveness.

Effect of zinc oxide nanoparticle size on the dielectric properties of polypropylene‐based nanocomposites

AbstractTo develop new environmentally friendly and recyclable high‐voltage cable insulation materials, the effects of the particle size of zinc oxide (ZnO) on the mechanical and electrical properties of nanocomposites were investigated based on a feasibility study of polypropylene (PP) as a high‐performance cable insulation material. The small particle size of ZnO can synergistically toughen PP with a polyolefin elastomer (POE), but the large particle size of ZnO leads to lower elongation at break. Adding ZnO nanoparticles can improve the bulk resistivity of the composites and suppress space charge injection. 0.5ZnO200 has the highest direct current and alternating current breakdown field strengths, 36.6% and 14.7% higher than PP/POE, respectively. This improvement may be due to the ability of 200 nm ZnO to introduce more deep traps. However, as the nanoparticle content rises and the particle size decreases, the agglomeration becomes more frequent, leading to the overlap of inter‐nano interfaces and reducing the modification effect of the nanoparticles. This study on the effect law of nano‐ZnO with different particle sizes on the microstructure, mechanical properties, and electrical properties of PP can provide a reference for developing new recyclable high‐voltage insulated cable materials.

Polyolefin Elastomer Modified Asphalt: Performance Characterization and Modification Mechanism

The rapid growth of traffic load and volume has put forward higher requirements for road durability. To extend the service life of roads, this work investigated the feasibility of using polyolefin elastomers with a two-phase molecular structure to simultaneously improve the high and low-temperature performance of asphalt. The characteristics of the polyolefin modifier were evaluated by differential scanning calorimetry first. Following evaluation, the storage stability, workability, and rheological properties of modified polyolefin-modified asphalt were measured through softening point difference, rotary viscosity, dynamic shear rheometer, and bending beam rheometer. Additionally, the engineering performance of modified asphalt mixtures was also investigated through Marshall stability, wheel-tracking, and three points bending experiments. The results show that polyolefin has two glass transition points which facilitate the simultaneous improvement of the high and low-temperature properties of asphalt. Meanwhile, no concerns are found about the storage stability and workability of polyolefin-modified asphalt. Furthermore, the results of rheological properties indicate that polyolefin can significantly enhance the deformation resistance at high-temperature and cracking resistance at low-temperature of asphalt binders. While the fatigue performance of the polyolefin-modified asphalt is slightly reduced, the residual Marshall stability, dynamic stability, and ultimate tensile strain of the asphalt mixture containing 8% polyolefin are 1.05 times, 1.31 times, and 1.17 times those of the control sample, respectively. The results of infrared spectroscopy demonstrate that there is no chemical reaction between the polyolefin-modified and the virgin asphalt. The improvement of polyolefin on asphalt performance can be explained by the existence of both “rigid” and “flexible” structures in polyolefin.

Corrosion effects in bifacial crystalline silicon PV modules; interactions between metallization and encapsulation

This study addresses the influence of different encapsulation materials on performance losses in bifacial PV modules after extended damp heat testing. The widely used ethylene vinyl acetate (EVA) is compared to polyolefin elastomers (POE) and thermoplastic polyolefins (TPO). We show that modules based on n-type bifacial solar cells (tunnel oxide passivated contact, TOPCON) are more prone to degradation than p-type (Passivated emitter rear cell, PERC) based laminates. More specifically, the front side metallization of these n-type cells corrodes under extended damp heat testing, yielding a decreased fill factor in the I–V characteristics and the appearance of dark spots and dark areas in electroluminescence imaging. The newer generation of encapsulant materials (POE and TPO), slowly replacing EVA in the modules commercialized today, demonstrate an improved protection of the metallization. Apart from the nature of the encapsulant, the cell type and the presence or absence of glass cover plates are also shown to influence the metal grid corrosion. To better understand the mechanisms at play, post-mortem analysis was carried out on small sized degraded PV laminates, by drilling out circular samples (“coring”) that could be analyzed in depth. The analyses revealed a weakened bond between the metallization and the silicon emitter, ultimately causing metal grid delamination. The proposed mechanism behind this delamination starts with the degradation of lead glass, which is part of the cell metallization grid and contains lead oxide (PbO). This compound is susceptible to dissolution in acidic environment.

Supercritical CO2Foaming of Lightweight Polyolefin Elastomer/trans-Polyoctylene Rubber Composite Foams with Extra-Soft and Anti-Shrinkage Performance

Lightweight polyolefin elastomer (POE) foams are of great interest in numerous fields. However, POE is difficult to foaming and obtaining the ideal cellular structures before cross-linking. Herein, low-molecular-weight trans-polyoctylene rubber (TOR) with lots of double bonds and low molecular weight was introduced into the POE matrix to improve their vulcanizing and foaming process. Then, a series of lightweight POE/TOR composite foams with adjustable cellular structures and outstanding performance were prepared by supercritical CO2 foaming. It was worth noting that the gel content and foaming temperature windows were greatly improved under the action of TOR, and a record-breaking density as low as 0.036 g/cm3 for POE-based composite foams was harvested. In addition, the as-prepared elastomer foams exhibited rapid shrinkage but slow recovery feature due to the diffusivity difference of gas and cross-linking nature of materials, and its recovery ratio could reach 91.3%. More interestingly, the conversion law of the corresponding density change between hard and soft materials was discovered, and extra-soft POE-based composite foams (like Shore C below 10) were obtained, which could be twisted, folded, compressed, stretched, bent, and rolled with ease. Furthermore, the residual strain and hysteresis loss ratio of as-prepared elastomer foams were as low as 1.56 and 12.95%, respectively. These distinct advantages together with the green foaming process make the composite elastomer foams very promising toward high-performance flexible cellular polymeric materials.

Effects of nano-silica on the crystallization, structure, and mechanical properties of crosslinked ethylene-octene copolymer/nano-silica composites

Abstract Nano-silica (SiO2) has been widely used to fill rubbers (crosslinked) and usual polyolefin elastomers (POEs). SiO2 filled POE with crystalline structure can also be crosslinked. Crystallization, structure, and mechanical properties of crosslinked POE/SiO2 composites can be affected by SiO2. In this paper, crosslinked POE/SiO2 composites were obtained through two different methods: dynamic crosslinking in molten state and static crosslinking. For the non-crosslinked and static crosslinked composites, SiO2 had a more significant effect on the nucleation in non-crosslinked POE than in static crosslinked POE. For the dynamic crosslinked composite, SiO2 and crosslinking points hindered the mobility of POE chains and suppressed the POE crystallization, resulting in smaller and fewer crystals. Dynamic mechanical analysis showed that the SiO2 and POE were compatible, as evidenced by the lower tan(δ) value in SiO2-filled samples. The latter was more consistent with the higher tensile strength and elongation at break for the non-crosslinked and static crosslinked composites than for the non-filled samples. However, the dynamic crosslinked composite exhibited the worst elongation at break, resulting from the lowest number of crystals and shortened molecular chains due to the shearing that occurred during crosslinking process. The SiO2 had no observable effect on the permanent deformation of samples.

Investigation and optimization of polyolefin elastomers polymerization processes using multi-objective genetic algorithm

The aim of this research is to develop continuous reactor network models to determine the reactor configuration and corresponding optimal operating conditions of a polyolefin elastomers polymerization process. To achieve this objective, a modified vapor-liquid equilibrium model is integrated with both the continuous stirred tank reactor (CSTR) model and the plug flow reactor (PFR) model to accurately predict the vaporization rates of liquid. The multi-objective problem is formulated to maximize the monomer conversion and minimize the total annualized cost simultaneously. To solve the multi-objective problem, the genetic algorithm is utilized to identify the optimal operating conditions. Furthermore, the impact of the reactor combination mode is analyzed by varying the number and sequence of CSTR or PFR. The research findings reveal that a multi-phase CSTR without circulating stream followed by a PFR is the optimal reactor configuration. The proposed configuration can enhance reactor productivity and reduce the total annualized cost simultaneously while meeting the desired polymer properties.

Lower Levelized Cost of Energy Achievement of Silicon Heterojunction Solar Modules with Low Water Vapor Transmission Rate Encapsulants

The damp‐heat (DH) degradation of silicon heterojunction (SHJ) solar modules leads to severe power loss, necessitating superior‐quality encapsulation materials. Herein, it is aimed to investigate the mechanical, thermal, and optical properties of ethylene vinyl acetate (EVA), polyolefin elastomer (POE), and thermoplastic polyolefin (TPO). TPO demonstrates the lowest water vapor transmission rate (WVTR) of only 3.14 g (m2·day)−1, which is approximately seven times lower than that of EVA. The Fourier transform infrared spectroscopy of EVA demonstrates a loss of the carbonyl group, revealing the formation of acetic acid under DH stress, which is not observed in POE and TPO. Both glass/back sheet and glass/glass (G/G) modules show a significant influence of encapsulant material on DH degradation. The maximum output power (Pmax) of the G/TPO/G single‐cell module maintains 96.6% of its initial value after 1000 h DH stress. After sealing the edge, the G/G commercial‐size modules encapsulated with lower WVTR encapsulants display excellent DH reliability, and Pmax degrades &lt;4.8% after 3000 h of DH stress. The predicted levelized cost of energy (LCOE) decreases ≈0.11 US cents/(KW h), which boosts additional power generation and illustrates the remarkable potential for the SHJ solar modules meeting the requirements of reliable, sustainable, and low‐LCOE systems.

Research on anti-aging properties of POE/SBS compound-modified asphalt in high-altitude regions

Styrene butadiene styrene (SBS)-modified asphalt ages prematurely in high-altitude regions, affecting the durability of asphalt pavement. To improve the anti-ageing properties of SBS-modified asphalt and delay the degradation of SBS in asphalt, polyolefin elastomer (POE), which has good resistance to oxygen, heat and UV, was added to SBS-modified asphalt for compound modification. The optimum dose of POE/SBS compound modification was selected by a rotating thin film oven (RTFOT) test and the asphalt samples were aged by two long-term ageing experiments (laboratory-simulated high-altitude ageing (SHA) and pressure ageing vessel (PAV)). Then the performance of asphalt before and after ageing was analysed through physical tests and rheological performance tests. In the mechanism analysis, the phase distribution and micromorphology of asphalt were analysed using fluorescence microscopy (FM) and atomic force microscopy (AFM). The changes in the four components, functional groups and relative molecular weight of asphalt were described using an asphalt chemical component test (four component method), Fourier transform infrared spectroscopy (FTIR) and gel permeation chromatography (GPC), respectively. Results showed that the optimum dose of POE/SBS compound modification was 3 % POE + 4 % SBS. The anti-aging properties of POE/SBS compound modified asphalt were better than those of SBS modified asphalt and the POE/SBS compound-modified asphalt possessed excellent high-temperature stability. The dispersibility of SBS in compound-modified asphalt was improved, and the excellent anti-ageing performance of POE phase in the compound system slowed down the degradation of the SBS phase. No new functional groups were produced when POE was added to asphalt before and after ageing. In the short-term ageing, the volatilization of light components and the agglomeration of small molecules play an important role, while the degradation of modifiers dominates in the simulated ageing process. During the simulated high-altitude ageing, the weight-average molecular weight generated by POE/SBS-modified asphalt was less than that of matrix asphalt, and POE/SBS compound-modified asphalt possessed good anti-UV ageing properties.

Configurational Entropy Regulation in Polyolefin Elastomer/Paraffin Wax Vitrimers by Thermally Responsive Liquid-Solid Transition for Force Storage.

The work output of shape memory polymers during shape shifting is desired for practical application as actuators. Herein, a polyolefin elastomer (POE) and paraffin wax (PW) are co-cross-linked by dynamic boronic ester bonds to enhance the network elasticity and the stress transfer between the two phases, endowing high force storage capacity to the prepared vitrimers. Depending on the phase of PW, one-way force storage is realized by programming at a low temperature (25 °C), owing to which solid PW can promote the locking of POE chains in a low-entropy state, while reversible force storage can be realized by programming at a high temperature (75 °C), owing to which the relaxation of chains facilitated by liquid PW can promote the construction of a stable structure. Based on one-way force storage, a weight-lifting machine with a weight of 20 mg prestrained at 25 °C can lift a 100 g weight, showing a lifting ratio of no less than 5000, with a high work output of 0.98 J/g. A high-temperature alarm can be triggered at varied temperatures (43-56 °C) through controlled force release by adjusting the PW content and programmed prestrains. Based on the reversible force storage, crawling robots and artificial muscles with a work output of 0.025 J/g are demonstrated. The dynamic cross-linking network also confers mold-free self-healing capability to POE/PW vitrimers, and the repair efficiency is enhanced compared with the POE vitrimer due to the improved POE chain motion by liquid PW. The realized one-way and reversible force storage and self-healing by POE/PW vitrimers pave the way for the application of SMPs in the fields of soft robotic actuators.