Search

Rheumatoid arthritis (RA) often leads to functional disabilities and deformities. MiRNA plays a vital role in cell pyroptosis. Nevertheless, the function and underlying mechanism of miR-144-3p in pyroptosis during the progression of RA remains unclear. In this study, N1511 cells were stimulated with IL-1β to construct a RA model. 3-(4,5-dimethyl-2-thiazolyl)-2,5-diphenyl-2-H-tetrazolium bromide (MTT) assay was performed to assess the cell viability. Cell pyroptosis was detected by flow cytometry. The levels of inflammatory cytokines (TNF-α, IL-6, and IL-18) were assessed by enzyme-linked immunosorbent assay (ELISA). The relationship among specific protein 1 (SP1), microRNA-144-3p (miR-144-3p), and phosphatase and tensin homolog (PTEN) was explored by dual-luciferase reporter assay, RNA immunoprecipitation (RIP), and chromatin immunoprecipitation (ChIP), respectively. The level of miR-144-3p in N1511 cells was upregulated by IL-1β. MiR-144-3p knockdown inhibited IL-1β-induced pyroptosis in N1511 cells, and the expressions of NOD-like receptor family pyrin domain containing 3 (NLRP3), Cleaved caspase-1, Gasdermin D (GSDMD), and Cleaved caspase-3 in IL-1β-stimulated N1511 cells were increased. The levels of inflammatory cytokines in N1511 cells were increased by IL-1β, which were restored by miR-144-3p knockdown. MiR-144-3p knockdown abolished IL-1β-induced inactivation of putative kinase 1 (PINK1)/Parkin RBR E3 ubiquitin-protein (Parkin) signalling. Moreover, transcription factor SP1 could upregulate miR-144-3p expression and miR-144-3p negatively regulated PTEN expression. In summary, MiR-144-3p induced by SP1 could promote IL-1β-induced chondrocyte pyroptosis via inhibiting PTEN expression and suppressing the activation of PINK1/Parkin signalling, which provided a new strategy against RA.

Two kinds of polyethylenes, high-density polyethylene (HDPE) with few chain branches and short-chain branched linear low-density polyethylene (LLDPE) with a relatively larger average molecular weight, were melt blended together in various mass ratios based on consideration of their practical applications. After identifying the good compatibility of the blends, their crystallization behaviors were studied by the successive self-nucleation and annealing (SSA) technique. The SSA analysis showed that not merely the number of melting fractions in the SSA curves changed with the blend composition, but also the content of the first two melting fractions at high temperature of SSA curves showed a positive deviation and a negative deviation with the blend composition, respectively. These phenomena, as well as the interesting appearance of a stepped increase of the lamellar thickness of each fraction with the highest temperature in each sample, indicated that co-crystallization occurred between HDPE and LLDPE. The ...

The organic nano-TiO2 was synthesized in reverse (W/O) microemulsion, using tetrabutyl titanate (TBOT) as precursor and γ-methacryloxypropyl trimethoxy silane (KH-570) as modifier. After phase inversion from W/O microemulsion to oil-in-water (O/W) emulsion, nano-TiO2/poly(methyl methacrylate) hybrid latex was prepared via in-situ polymerization based on the O/W emulsion containing organic nano-TiO2. Fourier transform infrared spectroscopy (FTIR) indicated that KH-570 was successfully grafted onto the surface of TiO2 particles. Transmission electron microscopy (TEM) and dynamic light scattering (DLS) demonstrated that the average diameter of nano-TiO2 was about 10 nm and the hybrid latex had obvious core-shell structure with particle size of 155 nm. The TBOT content and the mass ratio of KH-570 to TOBT have important effect on the polymerization stability and storage stability of the hybrid latex. When the TBOT content was 5% and the mass ratio of KH-570 to TOBT was 0.6, the coagulation rate (Cr) was 3.0% ...

N,N′-Dicyclohexyl-1,5-diamino-2,6-naphthalenedicarboxamide (NA), a highly efficient and selective β-nucleating agent for isotactic polypropylene (iPP), was synthesized and chemically supported on the surface of multiwall carbon nanotubes (MWCNTs) via an amidation reaction. The β-nucleation ability of NA, itself, is superior to the commonly used, highly efficient, and selective β-nucleating agents, e.g., commercial rare earth WBG-and aryl amide derivative TMB-5, as proved by the results of wide-angle X-ray diffraction (WAXD) and differential scanning calorimetry (DSC). The effect of MWCNTs supported NA (MWCNT-NA) on the crystallization and melting behavior of iPP was investigated by means of WAXD and DSC. The results show that the MWCNTs supported NA can effectively induce the formation of β-crystals in iPP/MWCNT-NA, although the grafting degree of NA onto the surface of MWCNTs could still to be improved.

In this study, high-melt-strength polypropylenes (PPs) were prepared by reactive extrusion of PP and varied amount of divinylbenzene in the presence of dicumyl peroxide and an antioxidant, and the dynamic rheological behavior, crystalline morphology, and fracture behavior of the resultant materials were investigated. It was found that at relatively low frequency, with the cross-linking and branching structures increasing, the complex viscosity of the melt of the modified PP increased significantly and then leveled off. The modulus of the melt, particularly the storage modulus, increased. The storage moduli of the melts with higher content of cross-linking and branching structures were higher than the loss modulus in the whole range of testing frequency, indicative of a completely elastic behavior. The crystallinity and the size of spherulites of the modified PP decreased, while the number of spherulites increased. The specific essential work of fracture and the specific non-essential work of fracture of t...

Polypropylene (PP) sheets obtained through a two-step process (masterbatch method) were crosslinked by electron beam irradiation. The crosslinked PP sheets were foamed in an oven under different processing conditions. The effects of foaming temperature and time on the mechanical properties and cell structure of PP foams were studied. With the foaming temperature increasing and foaming time lengthening, both the compression modulus and compression strength dropped. Scanning electron microscope (SEM) was employed to study the morphology and cell structure of different samples and the related morphology parameters were acquired. The results showed there was an optimum temperature and time that produced the maximum expansion ratio or the minimum foam density. As foaming temperature or time increased, the cell size increased and the cell density decreased regularly. Excessively high foaming temperature and overly long foaming time caused the coalescence and even the collapse of the cells.

Polypropylene (PP) blends based on isotactic polypropylene (iPP), propylene-ethylene block copolymer (bPP), and propylene–ethylene random copolymer (rPP) were prepared by melt blending and the effects of content of bPP and rPP on the shrinkage during solidification and storage and mechanical properties of the blends were studied. It was found that the addition of polypropylene copolymer could effectively reduce the processing shrinkage of iPP and the lowest shrinkage of the blends was achieved at a loading of 2 wt% bPP or rPP. The flexural modulus and tensile strength of the blends decreased a little while the impact strength and elongation at break were improved greatly compared with those of iPP.

High-temperature bulk thermolysis of high density polyethylene was performed to obtain degraded polyethylene, which was then left in an oxygen atmosphere for oxidation reaction at 160°C at different oxidation times, yielding a series of polyethylene degradation–oxidation products. Using infrared spectroscopy, chemical titration, gel chromatography, and differential scanning calorimetry, the structural changes of the polyethylene degradation–oxidation products were investigated. Hydroxyl, carboxyl, ester, and other functional groups were introduced into the molecular chains of oxidation products, and the number of carboxyl groups sharply increased with increasing oxidation time. The breaking of molecular chains as well as combination reactions, such as esterfication, during the oxidation process lead to decrease of number-average molecular weight () and increase of both weight-average molecular weight () and molecular weight distribution, and an initial increase and leveling off of the carboxyl number per ...

The distribution of the β-phase crystals of polypropylene (PP) in different zones of compression and injection moldings molded from PP-based dynamically vulcanized thermoplastic elastomer (TPV) in the presence of a β-nucleating agent (β-NA) was investigated. The influence of shear and cooling conditions and the addition of β-NA on the development of β-phase was examined and discussed based on the one-dimensional heat conduction behaviors with phase change. A hierarchical distribution of β-phase was observed in both compression- and injection-molded TPV/β-NA specimens. For the compression-molded TPV/β-NA specimens, the hierarchical distribution of β-phase induced by β-NA is dominated by the cooling conditions. For the injection-molded TPV/β-NA specimens, the occurrence of β-phase is also mainly induced by the addition of β-NA; the effect of shear on the relative content of β-phase can hardly be observed and the cooling conditions control the hierarchical distribution of β-phase. Both in compression and inj...

The effect of reaction time and mechanical stirring on thermal degradation of high density polyethylene(HDPE) was studied at 350°C under nitrogen atomosphere in a batch pressure reactor. Changes in molecular weight(MW), molecular weight distribution (MWD), and crystalline behaviors of the degraded products were investigated by gel chromatography (GPC) and differential scanning calorimetry (DSC). It was found that MWD curves all shifted toward lower molecular weight with increasing reaction time, with both the extent of the movement and its showing a rapid initial drop and then leveling off. In a short period of reaction time, the MW, MWD and crystalline behaviors of the degraded products were affected notably by the mechanical stirring. The of the degraded products without stirring was lower than that of products with stirring in the same time, which should be related to the large difference of temperature distributions in the reactor. When the reaction time reached 4 h, the of the degraded products had d...

The melt rheological behaviors in both linear and nonlinear regions were studied for binary blends of high-density polyethylenes (HDPEs) with unimodal molecular weight distribution (MWD). The surface distortion of the component resin with high-molecular-weight (HMW) and wide MWD through the capillary die could be alleviated with the addition of the component resin with low-molecular-weight (LMW) and narrow MWD. At the concentration of LMW component resin above 50 wt%, the negative deviation behavior (NDB) was observed in both the plots of dynamic storage modulus and complex viscosity versus the composition of the blends, furthermore, the Cole-Cole plot of the blend was below that of the pure LMW component, indicating the characteristics of immiscibility. However, the characteristic of homogeneity was revealed in the logG′∼logG″ curves that possessed almost identical slopes for all the blends. The anomalous phenomena were attributed to the slow diffusion of HMW ingredients in the blends, which was aggravat...

The influence of polyolefin elastomer (POE) content on the fracture behavior of injection-molded polypropylene (PP)/POE blends was evaluated by means of the essential work of fracture (EWF) method. The results indicated that the EWF approach worked well for the PP/POE blends when POE content was 0∼7.5 wt% of the blends. The specific essential work of fracture (w e) increased with increasing POE content, and the dominant factor that affected w e was the necking and subsequent fracture process. The specific nonessential work of fracture (βw p) slightly decreased with increasing POE content, while the specific plastic work (w p) showed an increasing trend with the decrease of the shape factor (β) of the specimen. Finally, it was shown that w e could be predicted reasonably well via the COD values.

Purified maleic anhydride grafted isotactic polypropylene (iPP-MA) and maleic anhydride grafted polyolefin elastomer (POE-MA) were used to coat synthetic mica, which was added to block polypropylene-co-ethylene (cPP) to prepare composites with 10 wt% mica content. The effect of the kinds of grafted polyolefin, their contents and composition ratios on the interfacial morphology, mechanical properties, crystallization behavior, and essential work of fracture parameters for the composites were studied. The results showed that the coating of synthetic mica with grafted polyolefin could effectively lower the surface polarity of the mica and improve the interfacial adhesion between mica and cPP. The sedimentation volume of mica reached a minimum, and the interface adhesion of the composites was comparatively good when the grafted polyolefin was 3 wt% of the weight of the mica. When the content of grafted polyolefin was fixed at 3–5 wt% of the weight of the mica, the sedimentation volume of mica decreased and th...

The strain rate, temperature, and microstructure-dependent, tensile-yielding behavior of three semi-crystalline polymers, namely high-density polyethylene (HDPE), polyamide 6 (PA6) and low-density polyethylene (LDPE), was investigated. It is found that, depending on the strain rate and temperature, the three polymers exhibit markedly different tensile deformation behavior, especially the shape of the stress-strain curves. LDPE exhibits a uniform extension and shows no obvious geometrically unstable effect, such as necking, during the overall tensile process. HDPE and PA6, on the other hand, show clear necking and cold-drawing phenomena during the uniaxial tensile process. When considering the effect of strain temperature on necking, significant differences between HDPE and PA6 emerge. For both, the heterogeneous necking disappears and homogeneous deformation occurs with increasing temperature. For HDPE, the homogeneous deformation takes place in the vicinity of the melting temperature, while for PA6, it t...

The change of storage moduli (G′), loss moduli (G″), zero shear viscosity, and complex viscosity were studied for a series of butene and hexene copolymerized linear low-density polyethylenes (LLDPEs) with various characteristics by investigating the dynamic rheological behaviors. It was found that: (1) the dependence of the complex viscosity on the weight average molecular weight did not follow the Raju equation; (2) the slopes of the G′∼ω and G″∼ω curves in the low-frequency regions not only were smaller than those of the polymers with monodisperse molecular weight, but also decreased with the relative molecular weight increasing or its distribution broadening; (3) the dynamic storage moduli G′ were more sensitive to the shear rate than the dynamic loss moduli G″; (4) the change of the dynamic moduli was directly correlated with the orientation and disorientation of the chain segments, which is influenced by the frequency or shear rate, the temperature, the molecular weight, and the molecular weight dist...

The effect of variation of injection conditions and addition of nano-calcium carbonate (CaCO3), nano-silicon dioxide (SiO2) and full-vulcanized nano-powdered styrene butadiene rubber (PSBR) on the shrinkage of injection-molded polypropylene-ethylene copolymer (90/10, co-PP) were investigated. The results showed that the shrinkage was different for different locations along the flow path. The shrinkage in the length direction of the injection-molded sample varied with the adjustment of the processing parameters, while the shrinkage in the width and thickness direction was almost unchanged. The addition of nano-CaCO3 and PSBR decreased the shrinkage of co-PP, while the shrinkage of co-PP/ SiO2 composite was almost unchanged.

The reaction of an ethylene-block-co-polypropylene (co-PP) with a polyfunctional monomer—divinylbenzene (DVB)—in the presence of dicumyl peroxide (DCP) was performed in a single screw extruder. It was found that the chain structure of co-PP was significantly influenced by the DVB concentration when the DCP content was fixed. Without DVB, degradation of co-PP chains, induced by DCP, mainly occurred. But when DVB was incorporated, reactions of crosslinking and branching prevailed in the system. The crystallization temperature of the modified co-PP was enhanced and the number of spherulites was increased, accompanied with a decrease of the spherulite size, due to the branched and crosslinked structure. The essential work of the fracture (EWF) method was adopted to characterize the fracture performance of the modified co-PP. The specific essential work of fracture, we, first decreased gradually to a minimum, and then climbed with increasing DVB concentration, which might be attributed to the variations of the...

Polypropylene (PP)/Ethylene‐propylene‐diene terpolymer (EPDM) blends were dynamically vulcanized with dicumyl peroxide (DCP), using a two‐step method of even dispersion of DCP in EPDM at first and then cross‐linking at elevated temperature. The results showed that though both chain scission and cross‐linking occurred, the cross‐linking reaction predominated in this process and the number of EPDM particles was increased, accompanied with a reduction in particle size and uniform dispersion. Differential scanning calorimetry (DSC) results indicated the existence of PP/EPDM graft copolymer. The essential work of fracture (EWF) results showed that both the specific essential work of fracture (w e ) and the specific plastic work (w p ) increased with increasing EPDM content, the fracture toughness and plastic energy consumption (βw p ) could be improved simultaneously and the ratio of w e and βw p could be controlled by adjusting EPDM and DCP content.

Two types of polypropylene (PP) with different molecular structure, namely, homogeneous PP (PPH) and PP block‐copolymer (PPC), were blended with a long chain, branched, low density polyethylene (LDPE) in a twin screw extruder and then injection moulded into test specimens; the mechanical properties and morphology of the blends are reported. The tensile strength, elastic modulus, flexural strength, and flexural modulus of the blends increased monotonically with increasing PP content, although exhibiting a slightly negative deviation from the rules of mixtures due to the relatively poor compatibility of the components, which caused the blends to separate into individual phases. Comparatively, these mechanical properties of the LDPE/PPH blend were much higher than that of the LDPE/PPC blend, which was attributable mainly to the fact that the mechanical properties of neat PPH are stronger than that of neat PPC. With respect to the impact strength of the blends, a maximum value appeared in LDPE/PPH blends when...

Through the lower‐melting temperature component processing (LTCP) of the blends (where the processing temperature of the lower‐melting temperature component in a blend is used), high interfacial contact (pseudo‐adhesion) in poly(ethylene terephthalate) (PET)/polyethylene (PE) and polycarbonate (PC)/PE blends is obtained from the difference in the contraction of the dispersed particles and the matrix during cooling from the processing temperature to room temperature. As a result of the pseudo‐adhesion, the tensile strength and modulus of the PET/PE and PC/PE blends with high interfacial contact are superior to those of their corresponding classical blends and, additionally, the PC reinforcement on the matrix is more noticeable than the PET. Morphological observation indicates that during uniaxial deformation at a tensile rate of 50 mm/min, numerous PC microfibers are in situ formed in the PC/PE blend, whereas in the PET/PE blend, ellipsoidal particles appear, resulting from slippage taking place b...