Peroxide-cured natural rubber (NR) reinforced by zinc dimethacrylate (ZDMA) was prepared. The cocrosslinking action of ZDMA and the formation and evolution of the phase morphology induced by ZDMA ...during the curing process were systematically investigated. A curemeter and a differential scanning calorimeter were used to investigate the cure kinetics, and the kinetic parameters and the apparent activation energy were obtained. The phase morphology of the composites obtained from transmission electron microscopy revealed that separated nanophases of poly(zinc dimethacrylate) (PZDMA) existed in the rubber matrix. Covalent crosslinking, physical adsorption, and ionic crosslinking simultaneously existed in the composites, and they were determined with an equilibrium swelling method. On the basis of this, new microstructure models of NR/ZDMA composites and ionic crosslinking were put forward.
Display omitted
•Superoxide dismutase mimicking centers with photothermal effect were constructed.•Responsive release of carbon quantum dots kills microbes intelligently.•Intelligent release of ...tanshinol exerts on-demand reactive oxygen species scavenging behaviors.•Balanced macrophage polarization promotes wound healing.
Promoting refractory wound healing remains a challenging issue. Currently, dressings with intelligent infection management functions built on infection eradication and reactive oxygen species (ROS) scavenging abilities are lacking. In this study, an approach based on Cu2+-imidazole coordination cross-linked histidine grafted chitosan (CS-His) and carbon quantum dots (CQDs) was developed to engineer superoxide dismutase (SOD) mimicking centers with photothermal anti-infection and intelligent anti-infection abilities, beyond typical ROS scavenging activity. The cross-linked coordination network was further promoted with tanshinol-encapsulated ZIF-8 frameworks (ZIF-8@Ts) to achieve intelligent infection management behaviors. These designs generate a refractory wound-healing hydrogel with integrated functions of photothermal anti-infection, SOD mimicking activity, and intelligent infection management. In response to infection exacerbation, the SOD mimicking centers and ZIF-8@Ts nanoparticles could release CQDs for anti-infection and Ts for antioxidation, respectively. In vitro results revealed photothermal anti-infection, ROS scavenging, and intelligent infection management capacities of the hydrogel. These abilities promoted the M2 transformation of macrophages and rescued the inhibitory effect of infection on fibroblast proliferation and migration. The hydrogel exhibited high regenerative efficacy in a rat model of chronically infected diabetic wounds. These results demonstrated the immense potential of the intelligent hydrogel integrated with multifunctions for refractory wound healing.
Natural rubber (NR) latex derived from
is a complex colloid comprising mainly rubber hydrocarbons (latex particles) and a multitude of minor non-rubber constituents such as non-rubber particles, ...proteins, lipids, carbohydrates, and soluble organic and inorganic substances. NR latex is susceptible to enzymatic attack after it leaves the trees. It is usually preserved with ammonia and, to a lesser extent, with other preservatives to enhance its colloidal stability during storage. Despite numerous studies in the literature on the influence of rubber proteins on NR latex stability, issues regarding the effect of protein hydrolysis in the presence of ammonia on latex stability during storage are still far from resolved. The present work aims to elucidate the interplay between protein hydrolysis and ammoniation in NR latex stability. Both high- and low-ammonia (with a secondary preservative) NR latexes were used to monitor the changes in their protein compositions during storage. High-ammonia (FNR-A) latex preserved with 0.6% (
/
) ammonia, a low 0.1% ammonia/TMTD/ZnO (FNR-TZ) latex, and a deproteinized NR (PDNR) latex were labeled with fluorescence agents and observed using confocal laser scanning microscopy to determine their protein composition. Protein hydrolysis was confirmed via sodium dodecyl sulfate-polyacrylamide gel electrophoresis (SDS-PAGE). The results revealed that protein hydrolysis increased with the storage duration. The change in protein composition accompanying hydrolysis also allows the spatial distribution of allergenic proteins to be estimated in the latex. Concurrently, the latex stability increased with the storage duration, as measured by the latex's mechanical stability time (MST) and the zeta potential of the latex particles. As monitored by AFM, the surface roughness of the NR latex film increased markedly during extended storage compared with that of the DPNR latex, which remained smooth. These results underscore the pivotal role of ammonia in bolstering NR latex stability brought on by protein hydrolysis, which greatly impacts latex film's formation behavior. NR latex stability underpins the quality of latex-dipped goods during manufacturing, particularly those for medical gloves.
Clay changes the strain-induced crystallization behavior of natural rubber and induces a dual crystallization mechanism due to the orientation of clay layers during deformation. The structure ...evolution was probed by in-situ synchrotron wide-angle X-ray diffraction, while the thermodynamics of the onset of crystallization was analyzed by the tube model. The entropy change required for the onset of the strain-induced crystallization of the clay filled rubber is composed of the entropy reduction due to the rubber–filler interactions and also the stretching. The summation of the two kinds of the entropy reduction is nearly equal to that of the neat rubber. The thermodynamic analysis reveals that the orientation of clay layers along the direction of stretching reduces the chain conformational entropy and changes the crystallization mechanism. These results give some new insights into the strain-induced crystallization process and the reinforcement mechanism for the clay filled rubber.
Display omitted
In order to reduce the environmental pollution caused by waste rubber and to realize the recycling of resources, we proposed a facile method for the hydrophilic modification of waste rubber powder ...(HRP) and used it to reinforce a composite hydrogel. In the presence of toluene, dibenzoyl peroxide (BPO) diffused into the waste rubber powder. After the solvent was removed, BPO was adsorbed in the rubber powder, which was used to initiate the grafting polymerization of the acrylamide monomer on the rubber-water interface. As a result, the polyacrylamide (PAM) molecular chains were grafted onto the surface of the rubber powder to realize hydrophilic modification. The success of the grafting modification was confirmed by FTIR, contact angle testing, and thermogravimetric analysis. The hydrophilic modified waste rubber powder was used to reinforce the PAM hydrogel. Mechanical tests showed that the tensile strength and elongation at the break of the composite hydrogel reached 0.46 MPa and 1809%, respectively, which was much higher than those of pure PAM hydrogel. Such a phenomenon indicates that the waste rubber particles had a strengthening effect.
Abstract
In order to study the influence of freeze-thaw cycle on the flexural performance of asphalt pavement, semi-circular flexural test (SCB) is carried out. Coal gangue powder (accounting for 0%, ...25%, 50%, 75% and 100% by weight of ore powder) is used to replace ore powder to improve the freeze-thaw resistance of asphalt.According to the test data, the load-displacement curve is drawn, the ultimate tensile stress(
σ
t
) is studied, and the variation law of different coal gangue powder replacement rates under different freeze-thaw cycles (0, 2, 4, and 6 times) is analyzed by ultimate tensile stress. The test results show that the best replacement rate of coal gangue powder is 50%, and
σ
t
decreases with the increase of freeze-thaw cycles, so adding coal gangue powder can reduce the influence of freeze-thaw cycles on the bending performance of asphalt pavement. By analyzing the load-displacement curve, energy indexes such as W
D
(total work from initial failure to complete failure), W
U
(energy dissipation from initial failure to complete failure), W
S
(work from initial failure to specimen failure) and
η
are obtained. In the freeze-thaw cycle, with the increase of cycle times, the energy consumption of W
D
, W
U
and W
S
decreases, which aggravates the damage of asphalt mixture and reduces the flexural capacity of specimens. Among them, six freeze-thaw cycles have the lowest flexural capacity of specimens, indicating that freeze-thaw damage directly affects the flexural performance of asphalt mixture.
Building energy baseline models, particularly machine learning-based models, are a core aspect in the evaluation of building energy performance to identify inefficient energy consumption behavior. In ...smart city design, energy planners and decision makers require comprehensive information on energy consumption across diverse building types as well as comparisons between different types of buildings. However, there is no comprehensive study of baseline modeling across the main building types to help identify factors that influence the performance of different machine learning algorithms for baseline modeling. Therefore, the goal of this paper is to review and analyze energy consumption behavior and evaluate the prediction performance and interpretability of machine learning-based baseline modeling techniques across major building types. The results have shown that the Extreme Gradient Boosting Machine (XGBoost) model is the most accurate baseline modeling method for all building types. Time-related factors, especially the week of the year and the day of the week, have the most impact on energy consumption across all building types. This study is presented as a useful resource for smart city energy managers to help in choosing and setting up appropriate methodologies for better operational effectiveness and efficiencies when designing and planning smart energy systems.
HIV and sexually transmitted infections (STIs) are major global public health concerns. Over 1 million curable STIs occur every day among people aged 15 years to 49 years worldwide. Insufficient ...testing or screening substantially impedes the elimination of HIV and STI transmission. The aim of our study was to develop an HIV and STI risk prediction tool using machine learning algorithms. We used clinic consultations that tested for HIV and STIs at the Melbourne Sexual Health Centre between March 2, 2015, and December 31, 2018, as the development data set (training and testing data set). We also used 2 external validation data sets, including data from 2019 as external “validation data 1” and data from January 2020 and January 2021 as external “validation data 2.” We developed 34 machine learning models to assess the risk of acquiring HIV, syphilis, gonorrhea, and chlamydia. We created an online tool to generate an individual’s risk of HIV or an STI. The important predictors for HIV and STI risk were gender, age, men who reported having sex with men, number of casual sexual partners, and condom use. Our machine learning–based risk prediction tool, named MySTIRisk, performed at an acceptable or excellent level on testing data sets (area under the curve AUC for HIV=0.78; AUC for syphilis=0.84; AUC for gonorrhea=0.78; AUC for chlamydia=0.70) and had stable performance on both external validation data from 2019 (AUC for HIV=0.79; AUC for syphilis=0.85; AUC for gonorrhea=0.81; AUC for chlamydia=0.69) and data from 2020-2021 (AUC for HIV=0.71; AUC for syphilis=0.84; AUC for gonorrhea=0.79; AUC for chlamydia=0.69). Our web-based risk prediction tool could accurately predict the risk of HIV and STIs for clinic attendees using simple self-reported questions. MySTIRisk could serve as an HIV and STI screening tool on clinic websites or digital health platforms to encourage individuals at risk of HIV or an STI to be tested or start HIV pre-exposure prophylaxis. The public can use this tool to assess their risk and then decide if they would attend a clinic for testing. Clinicians or public health workers can use this tool to identify high-risk individuals for further interventions.
In this paper, graphene oxide (GO) and carbon nanotube (CNT) hybrid fillers were used to replace partial carbon black (CB), and GO/CNT/CB/NR composites were prepared with excellent crack growth ...resistance, low heat build-up and superior mechanical properties. Mechanical testing revealed a significant synergistic reinforcement between GO/CNT and CB in NR composites. The improved dispersion of GO/CNT hybrid fillers and CB in the NR matrix was characterized by transmission electron microscopy (TEM). Through the fatigue test, the GO/CNT/CB/NR composites showed excellent fatigue crack growth resistance and low heat build-up compared to CB/NR composites. These properties provide the NR composites with better applications in industry.
In situ studies of strain-induced crystallization in unfilled and multiwalled carbon nanotube (MWCNT)-filled natural rubber (NR) were carried out by using synchrotron wide-angle X-ray diffraction ...(WAXD). Synchrotron WAXD results indicate that more nuclei appear in the MWCNT-filled NR sample, leading to higher crystallinity, lower onset strain of crystallization, and remarkable enhancement in tensile strength. During deformation, despite the amorphous chains remaining in isotropic orientation, the domains of larger scale (10−100 nm) with high network chain density in the NR matrix are oriented. The MWCNTs induce significant variation of this orientational process, and it is monitored by the stearic acid (SA) crystallites, which are effective nanoprobes of the amorphous phase. The results indicate that a small amount of MWCNTs and SA crystallites can be used as new tools to analyze the microstructural orientation of NR during deformation. The results also yield new insight into the strain-induced crystallization mechanism.
PDF
