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China is the largest country in the trade of juvenile products in the world. However, the products suffered the loss of technical barriers to trade from Europe and the United States of America increased year by year. This paper analyzes the standard system of juvenile products in Europe and the United States of America with the method of standard comparison, to find its relative technical advantages, explore the reasons for the recall notification of juvenile products exported to the above regions by China, propose strategies for breaking down the technical measures of trade, and promote the development of international juvenile product export trade.

China is the world’s largest manufacturer and exporter of juvenile products, while the standardization system for juvenile products still needs to be perfected and still has a certain gap with foreign advanced systems. To promote the standardization of juvenile products in China and solve the limitations of the existing standards system, the “Standardization Working Group on Juvenile Products” was established in May 2020 with the approval of the Standardization Administration of China. The development trend of juvenile products industry in China was analyzed in this paper, teases out the existing problems in the development of standardization, and establishes the National standardization system for juvenile products according to the working scope of the “Standardization Working Group on Juvenile Products”.

To explore whether radiomic features of perihematomal tissue can improve the forecasting accuracy for the prognosis of patients with an intracerebral hemorrhage (ICH).In total, 118 ICH patients were retrospectively studied that had a clinical and radiological diagnosis of spontaneous ICH. The functional outcome 3 months after ictus was measured using the modified Rankin Scale (mRS), which was divided into good (mRS ≤ 2) and poor outcomes (mRS 2). A total of 2260 radiomics features were obtained from non-contrast computer tomography (NCCT) images, with 1130 features extracted from the hematoma and the hematoma plus perihematoma. The high-dimensional data was modeled by a logistic regression algorithm and the accuracy of the model was verified by five-fold cross-validation. The predictive performance of radiomics models was assessed by the area under the receiver operating characteristic (ROC) curve.In the test set, the mean ROC area under the curve (AUC) of the hematoma set to predict the prognosis of ICH was 0.83, and the specificity and sensitivity were 78% and 81%, respectively. When the hematoma and perihematomal tissue were combined, the mean AUC increased to 0.88, and the specificity and sensitivity reached 85% and 84%, respectively. The hematoma plus perihematoma model showed a significantly higher AUC and specificity.Analysis of the hematoma and perihematomal tissue NCCT-based radiomics could potentially identify the progression of a hematoma more accurately and could be a valuable clinical target to enhance the prediction of outcomes in patients with ICH.

Organically modified montmorillonite (OMMT) was incorporated into the complex of 18-crown-6 (CE) and polyimide-croum ether (PI[CE]), and its effect on the properties of the complex was evaluated in terms of thermal behaviors, coefficient of thermal expansion, mechanical properties, dynamic mechanical properties and water absorption. The results indicate that the overall properties of PI[CE] complex are obviously enhanced. A very low coefficient of thermal expansion of 17.9 ppm/K, a high tensile strength of 124.5 MPa, and toughness of 30.8 MJ/m3 can be achieved for the OMMT/PI[CE] nanocomposite with 3wt% OMMT. Meanwhile, the thermal stability of the PI[CE] complex is improved, and its 5% weight loss (Td5%) and Tg increase by 10.6 and 23.0 °C, respectively, and the water absorption rate decreases from 1.73% to 1.13%. The homogeneous dispersion and strong interactions of OMMT with PI[CE] matrix are responsible for the superior properties of the nanocomposites according to SEM and XRD results.

A novel hydroxyl-containing polyimide (PI-OH) has been successfully synthesized and subsequently used as a new colorimetric and ratiometric chemosensor for the detection of F− with high selectivity and a fast response time. The ratiometric absorbance changes of the chemosensor PI-OH in DMSO solution show a linear response to F− in the concentration range of 0–0.50 mM with a detection limit of 1.79 μM, which provides a quantitative method for F− detection. 1H NMR titration and DFT calculation studies confirm the F− sensing mechanism involves H-bond interactions and subsequent deprotonation in the chemosensor. Moreover, the chemosensor PI-OH in DMSO solution can be reversed many times and applied to the visual detection of F−. Finally, PI-OH film has been fabricated for real-time visualization of F− with high selectivity and sensitivity. The F− bonded to the PI-OH film can be easily removed by immersing it in acidic solution to recover the sensing ability to F−. X-ray photoelectron spectroscopy and energy dispersive spectroscopy analysis indicate that hydroxyl groups in the PI-OH film can bond to F− and the bonded F− can be removed quantitatively. This work provides not only a novel PI film-based sensor device for the visual and reversible detection of F− with high-efficiency, but also a promising F− extractor.

Some commercially available graphene (CG) samples, actually graphite nanoplates, are difficult to be applied in polymers due to their large thickness, even though their fabrication is more cost-effective. In this work, a CG sample with a thickness of about 25 nm is pre-treated via a facile acid soaking technique, and then the acid-treated CG is introduced into epoxy resin (EP) to improve the toughness while maintaining the high rigidity of the EP. The thickness of the acid-treated CG is dramatically decreased to about 1 nm, well-dispersing CG in the EP matrix. The tensile strength and the fracture energy of EP composite with 0.2 wt% acid-treated CG are increased to 85.2 MPa and 3.6 kJ m−2 from 74.3 MPa and 2.3 kJ m−2 of pure EP, respectively. In addition, the tensile-fractured surfaces of EP composites reveal that the toughening mechanism is mainly attributed to the crack deflection and crack pinning caused by the firmly-embedded CG nanosheets in the EP matrix. Besides, the glass transition temperature of EP composites is increased to 170.5 °C from 163.9 °C of pure EP. The present study provides a valuable approach for making use of the cost-effective graphite nanoplates to achieve a similar performance as graphene in EP.

To explore the high performance epoxy resin with high thermal properties and low dielectric constant and loss for copper clad laminates (CCLs), poly(phenylene oxide) (PPO) with low molecular weight is usually used as a modifier. Toward this end, a fluorinated redistributed poly(phenylene oxide) (F-rPPO) with number-average molecular weight of 3.0 ~ 6.2 × 103 g/mol was synthesized via the redistribution reaction of commercial PPO with 4,4′-(hexafluoroisopropylidene) diphenol (BPAF) using benzoyl peroxide (BPO) as an initiator. The structure of F-rPPO was characterized by 1H NMR, 19F NMR and FT-IR, respectively. F-rPPO was employed in the modification of diglycidyl ether of bisphenol A (DGEBA)/methylhexahydrophthalic anhydride (MeHHPA) epoxy resin, and the effect of F-rPPO on the curing behaviors and resulting thermosets were investigated. The results showed that the cured EP/F-rPPO resins exhibited improved thermal and dielectric properties, as well as lower moisture absorption. At 40 phr F-rPPO (based on DGEBA), the cured EP/F-rPPO resin possessed a higher Tg of 146 ℃ and Td5% of 363 ℃ than that of 129 ℃ and 321 ℃ for the pristine epoxy resin, respectively. Moreover, EP/F-rPPO exhibited a lower moisture absorption (0.33%), dielectric constant and loss (2.69 and 0.0132 at 12 GHz) compared to the pristine epoxy resin (0.48%, 2.93 and 0.0303 at 12 GHz, respectively). This work provides an easy and effective solution to fabricate the high performance epoxy resins modified by PPO to better meet the requirement of CCLs.

A new approach to synthesize fluorine-containing graphene oxide (FCGO) was proposed, in which a less toxic reagent was used rather than fluorine gas or anhydrous hydrogen fluoride. The dielectric and mechanical properties of polyimide composites were improved by incorporating a small amount of FCGO. FCGO served as not only nanofiller to lower the dielectric constant of PI films but also inorganic toughening particles to improve the toughness of PI films. The dielectric constant of PI films with 0.6 wt % FCGO was decreased from 3.33 for pure PI to 2.34. In addition, both the tensile strength and Young’s modulus of PI films with 0.6 wt % FCGO were increased to 141 MPa and 4.95 GPa from 118 MPa and 2.81 GPa for pure PI, respectively. In addition, its tensile energy to break was enhanced to 31.6 MJ/m3 from 20.8 MJ/m3.

Low dielectric constant is desired for polyimide to be used in microelectronic industry. In the present study, a series of porous graphene fluoroxide/polyimide (GFO/pPI) nanocomposite films with improved dielectric and mechanical properties were fabricated. Polyethylene glycol (PEG) was introduced into the system to play the roles of an intercalator in exfoliation of graphite fluoroxide and a blowing agent in preparation of porous structure. The in-situ bubble-stretching, resulting from PEG decomposition during the thermal imidization, not only hindered the agglomeration of GFO nanosheets, but also generated micro-pores in PI matrix. Both the porous structure and the GFO nanosheets significantly decreased the dielectric constant of composite films, and the load transfer between GFO and PI matrix efficiently improved the mechanical properties of composite films. A very low dielectric constant of 2.29 as well as high tensile modulus of 4.43 GPa and tensile strength of 159 MPa was obtained for the composite film with the GFO loading of only 0.30 wt%. In addition, the glass transition temperature of GFO/pPI films was increased from 355 °C to 388 °C, and the coefficient of linear thermal expansion of GFO/pPI films was decreased from 48.7 ppm/K to 24.9 ppm/K. Keywords: Polyimide, Graphene fluoroxide, Micropores, Dielectric property, Mechanical properties

A novel aromatic diamine containing pyridyl side group, 4-pyridine-4,4-bis(3,5-dimethyl-5-aminophenyl)methane (PyDPM), was successfully synthesized via electrophilic substitution reaction. The polyimides (PIs) containing pyridine were obtained via the microwave-assisted one-step polycondensation of the PyDPM with pyromellitic dianhydride (PMDA), 3,3′,4,4′-biphenyltetracarboxylic dianhydride (BPDA), 3,3′,4,4′-diphenylether tetracarboxylic dianhydride (ODPA) and 4,4′-(hexafluoroisopropylidene)diphthalic anhydride (6FDA). Contrarily to the reported similar PIs, these PIs exhibit much higher thermal stability or heat resistance, i.e. high glass transition temperatures ( T g s) in the range of 358–473°C, and the decomposition temperatures at 5% weight loss over 476°C under nitrogen. They can afford flexible and strong films with tensile strength of 82.1–93.3 MPa, elongation at break of 3.7%–15.2%, and Young's modulus of 3.3–3.8 GPa. Furthermore, The PI films exhibit good optical transparency with the cut-off wavelength at 313–366 nm and transmittance higher than 73% at 450 nm. The excellent thermal and optical transmittance can be attributed to synthesis method and the introduction of pyridine rings and ortho-methyl groups. The inherent viscosities of PIs via one-step method were found to be 0.58–1.12 dl g −1 in DMAc, much higher than those via two-step method. These results indicate these PIs could be potential candidates for optical substrates of organic light emitting diodes (OLEDs).

Unsatisfied overall properties and high-cost production are major obstacles for the commercialization of polyimide (PI) films. This work aims to develop a convenient way with low cost to prepare multifunctional PI films with excellent combined properties of low dielectric constant (k), high transparence and fluorescence by the direct structural modification on easily available PIs containing active groups. Thus, a series of fluorene-based PIs with tert-butyldimethylsiloxy (TBS) side groups (PI-TBSs) were successfully synthesized by a direct silyl ether reaction of hydroxyl-containing PIs (PI-OHs) with tert-butyldimethylsilyl chloride (TBSCl). The resulted PI-TBSs with high yield are readily soluble in many common solvents, even in low-boiling-point solvents at room temperature. Due to the presence of the cardo-type fluorene structure, PI-TBS films still possess the excellent thermal properties with a glass transition temperature (Tg) of 311.2–338.9 °C and a 5% weight loss temperature (T5%) of 469.5–506.4 °C in N2 and the good mechanical properties with a tensile strength (TS) of 57.7–79.1 MPa. In addition, PI-TBS films exhibit the light color with the high optical transparence (over 80% at 450 nm), the low dielectric constant (as low as 2.44 at 1 MHz for PI-TBS-2F) and the bright fluorescence because of the reduced charge transfer (CT) interaction in PI chains chemically bonded by bulky non-polar TBS groups. As the result, this work provides a convenient way to prepare multifunctional PI films with the excellent overall properties, which show high potential applications of these PI films in microelectronic, electric and photonics industries.

Here, four cardo-type polyimides containing hydroxyl groups have been successfully synthesized by one-step solution polymerization of a hydroxyl-containing fluorene diamine monomer and various commercial dianhydride monomers. The obtained PIs with high molecular weights were readily soluble in many polar solvents. Simultaneously, they still maintain the excellent thermal stability (the 5% and 10% weight loss temperatures over 480 °C and 510 °C in nitrogen, respectively) and the high glass transition temperatures (Tgs, 342–442 °C). Furthermore, PI films show high tensile strength (>78 MPa) and relatively high optical transparency (over 82% at 500 nm), except PI-4. Utilizing that hydroxyl group in PI chain is able to form H-bond interaction with F−, these hydroxyl-containing PIs in DMSO solution are successfully applied as colorimetric chemosensors for detection of F− with high selectivity and sensitivity. Finally, the PI film chemosensors is also used for visual and reversible sensing of F−, which enables them to be a fast and portable test kit for visible detection of F−.

Functional graphene oxide (FGO) with photosensitivity was incorporated into the photosensitive polyimide (PSPI) matrix via solution blending, to prepare the photocrosslinkable nano-composite films. The crosslinked composite films were obtained through UV irradiation. FGO was well dispersed in PSPI matrix and effectively covalently bonded to PSPI main chains through photo-chemical reaction. Due to the confine of electronic polarization caused by the crosslinked structure, the dielectric constant (k) and dielectric loss tangent (tan δ) of the crosslinked PSPI/FGO films decreased effectively, which could be tuned by varying both the UV irradiation time and FGO loading. Among all the composite films, the film with 0.5 wt% FGO content exposed under UV light for 900 s had the lowest k (2.58) and tan δ (0.026) values at 10 MHz. These findings suggest that PSPI/FGO composite films are promising application in the field of photoresist with low dielectric constant.

An amphiphilic alternating copolymer with hydrophobic polyhedral oligomeric silsesquioxane (POSS) segments and hydrophilic anhydride segments, which is able to self-assemble into nanoscale POSS aggregates, is introduced into fluorinated polyimide (FPI) films to polish up their toughness while lowering their dielectric constant. The dielectric constant of POSS/FPI composite films with 2.8 wt% amphiphilic alternating copolymer significantly decreases to 2.09 from 3.14 for pure FPI. Furthermore, a sharp brittle-ductile transition is observed in the tensile energy to break versus interparticle distance curve. When the interparticle distance is reduced to 215 nm, the elongation at break and tensile energy to break of POSS/FPI composite films increase to 27.5% and 23.5 MJ/m3 from 8.3% to 6.8 MJ/m3 respectively. The tensile-fractured surfaces of POSS/FPI composite films reveal that the toughening mechanism is mainly attributed to the prevention of crack propagation and the debonding of POSS aggregates with a plastic void growth.

As a new graphene derivative, graphene fluoroxide (GFO) has not been fully studied because of its complex preparation process. In this paper, two simple methods, a modified Hummers' method and an improved method, were adopted to oxidize unsaturated commercial graphite fluoride (GIF) to prepare graphite fluoroxide (GIFO), the precursor of GFO. GFO was finally obtained via liquid-phase ultrasonic exfoliation of GIFO in organic solvents. Multiple spectroscopic techniques were used to characterize GIFO and GFO. The test results indicate that both of the two methods can covalently bond oxygen functional groups to graphene fluoride (GF) sheets successfully, but the modified Hummers' method gives higher yield and oxidizability. The structure of the GFO sheet is confirmed as few-layer by its atomic force microscopy results and transmission electron microscopy images. UV-vis and fluorescence emission measurements suggest that introducing oxygen groups into GF sheets can change their optoelectronic properties. Based on this, GFO with tunable optoelectronic properties might be facilely obtained in large batches through oxidization and liquid-phase exfoliation of unsaturated GIF with different fluorine coverage.