•The glass transition temperature was found to be independent of crystallinity.•The glass transition temperature can be predicted as function of RAF–MAF content.•A higher content of RAF leads to a ...higher glass transition temperature.•No clear correlation between RAF–MAF content and the crystal unit cell was found.•Flash-DSC was combined with time-resolved, in situ X-ray (WAXD) measurements.
The glass transition temperature (Tg) is a crucial parameter for understanding the mechanical behavior of polyamide 6. It depends mainly on two aspects: hydration level and processing, i.e. the thermal history and the flow conditions. In this work, the effect of the thermal history on Tg was investigated by means of fast scanning calorimetry (flash-DSC). Two different solidification procedures were studied; isothermal crystallization and continuous cooling were performed at different temperatures and rates respectively. The procedures have led to two contradictory trends of glass transition evolutions when related to their crystallinity fraction. The concept of rigid amorphous phase is used. This is considered as a part of the amorphous phase with a lower mobility, present at the inter-phase between crystals and bulk amorphous (mobile amorphous fraction). The analysis leads to the conclusion that the thermal history affects the ratio between rigid and mobile amorphous phases and it is this ratio that determines the glass transition temperature of dry polyamide 6.
•DOPO coating is constructed by hydration reaction.•DOPO coating with a super-low p content displays good flame retardancy and anti-dripping ability on PA6 fabric.•DOPO coating effectively inhibits ...heat propagation and improves fire safety.•DOPO coating mainly works in gas-phase.
The application of insoluble 9,10-dihydro-9-oxa-10-phosphaphenanthrene-10-oxide (DOPO) to develop a durable coating for flame retardant (FR) modification of polyamide 6 (PA6) is of concern and difficult. This study found that the hydration reaction of DOPO provided the possibility of constructing a DOPO coating. Hence, DOPO compound was deposited onto PA6 fabric by dip-coating technique. Then, the impacts of DOPO coating on FR performance, anti-dripping property, smoke and heat release performance of coated PA6 fabric were systematically studied. The limiting oxygen index (LOI) of PA6 fabrics continued to increase with the increase of phosphorus content. However, the coated PA6 fabrics achieved anti-dripping property at a phosphorus content of 0.88 ∼1.75 mg/g. Besides, the heat release ability of coated PA6 reduced sharply at high phosphorus content of 1.75 mg/g, as suggested by a reduction of 20.9% and 21.8% in pHRR and THR, respectively. Moreover, DOPO coating exhibited good washing durability on PA6 fabric because of the hydrogen bond formed between DOPO and PA6, as well as the adhesion of DOPO coating. The coated PA6 fabric could still self-extinguish after 15 washing cycles. Further analysis proved that DOPO played a quenching role in the gas-phase with a weak condensed-phase action. This work points out the right direction for the future research on the preparation of FR PA6 fabric using DOPO derivatives.
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Polymer blending is a typical and conventional approach for integrating the excellent physical/chemical properties of individual polymer components. Specifically, the mechanical toughness and ...strength of polyamide-6 (PA6)/polyketone (PK) blend are substantially enhanced compared to either PA6 or PK individual component. Nevertheless, there are few atomic-level insights into such mechanical property enhancement. In this study, solid-state nuclear magnetic resonance (NMR) is utilized as a main tool to understand the molecular origin of the mechanical enhancement of PA6/PK blends. The proton relaxation times are used to evaluate the miscibility and domain sizes in PA6/PK blends, and to determine the crystallinity of each component, where both conventional DSC and WAXD experiments fail because of similar crystallization/melting behaviors of PA6 and PK components. 2D 1H–13C WISE (wideline separation) and HETCOR (heteronuclear correlation) solid-state NMR spectroscopy were performed to further reveal the nano-heterogeneous structures and hydrogen bonding interactions in PA6/PK blend. With further combination with FTIR and SEM results, the previous characteristic morphological model for elucidating the toughening mechanism for PA6/PK blends is refuted, and it is proposed that the superior performance of PA6/PK blend is resulted from the synergistic effects of enhanced interfacial adhesion and interconnected interphase percolated in the bulk PA6/PK blends via hydrogen bonds. We envisage the detailed molecular level insights provided by solid-state NMR spectroscopy could assist in the bottom-up design of high performance polymer blend materials.
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•The locations of hydrogen bonding between PA6 and PK are precisely determined.•The strength of hydrogen bonding interactions is semi-quantitatively characterized.•A complementary approach for studying crystallization of polymer blends is provided.•Insights into the toughening mechanism via solid-state NMR techniques are obtained.
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•A PA6/Cu-f network was prepared via melt temperature variety of two PA6 particles.•Cu flakes coated with PA6 (low melt temperature) were fabricated by S3M technology.•PA6/Cu-f ...network had a record high thermal conductivity at 6.3 Wm−1Κ−1.•PA6/Cu-f network showed reduced interface thermal resistance.•The composite possessed outstanding thermal management during LED lamps cooling test.
Polymer plays an essential role in efficient thermal management of high-performance electronic devices, but the cooling efficiency of polymer composites is limited by some technical difficulties, such as the lack of thermal transport pathways and high cost of nano filler. Herein, we introduced solid-state shear milling (S3M) technology to prepare copper flakes (Cu-f) and constructed an enhanced Cu flakes network through hot-pressing of Cu and polyamide 6 (PA6) particles with different melt temperature. The low melt temperature PA6 coating on Cu flake surface acted as a glue to tightly connect Cu flakes and high melt temperature PA6 particles, thus generating an enhanced filler network. This brings the PA6/Cu-f network composites with a record high thermal conductivity at 6.3 Wm−1Κ−1, which is 3 times higher than that of traditional PA6/Cu-s composites (1.8 Wm−1Κ−1) at 80 wt% Cu loading. Basing on Foygel’s model from effective medium approximation theory, the PA6/Cu-f network composites had a lower thermal contact resistance (Rc) of 9.8 × 103 KW−1 and interfacial thermal resistance (ITR) of 6.3 × 10−8 W−1m2K. In LED lamps cooling performance test, PA6/Cu-f network composite showed 15 °C lower than traditional PA6/Cu-s composite in operating temperature. We believed that with the excellent thermal management ability and low cost, the PA6/Cu-f network composites open up opportunities for efficient thermal management in high power density devices.
Membranes of anion channels in matrix were constructed through amphiphilic self-assembly of polyelectrolyte, SO3H group containing polyamide 6 (SPA6). SPA6 molecules self-aggregated into 255 nm ...micelles with negative charges at the surface in casting solution. Micelles switched into nanofibers, which formed pompoms of divergent arrangement of nanofibers from the center after immersed in coagulation bath. They adhered and piled up to construct the membrane. Charged groups were remained at the surface of pompoms during solidification. The gaps between spheres provided channels full of anions, which supplied great repulsion to anions. It endowed membranes the potential to remove anion dyes from aqueous solution. The rejection was up to 99.73% for 500 mg/L Congo red and 85.68% for 100 mg/L Acid blue 93 and 63.06% for 100 mg/L Methyl orange after first filtration. Total removal percentage was 95.48% for Acid blue 93 and 79.51% for Methyl orange after second filtration. Self-aggregation of dye molecules also helped their high removal efficiency. Flux of film 30 M of 100 mg/L CR solution dropped to 67.34% and rejection rate was higher than 95% in 1500 min. Flux could be brought back to more than 90% of the original values after washed by deionized water, suggesting that 30 M had good anti-fouling capacity. SPA6 membranes displayed a potential for effective treatment of textile wastewater.
•Membrane rejection for 500 mg/L Congo red solution was 99.71% at 0.1 MPa.•The rejection for 100 mg/L Congo red solution declined to 95.31% after 1500 min.•Electrostatic repulsion and pore size screen determined the removal of anionic dyes.
An integrated multi-functional additive was fabricated by successively grafting melamine (MEL) and phytic acid (PhA) on multiwalled carbon-nanotubes (MWNCTs), and was then applied in PA6 to improve ...the flame retardancy and light aging resistance of the composite. The limit oxygen index of PA6 composite containing 7 wt% PhA-MEL-MWCNTs was increased to 26.4 from 21.0. The smoke and CO release were significantly reduced by 48% and 88% respectively, and the severe melt dripping of PA6 in burning was eliminated. It is proved that PhA-MEL-MWCNTs can absorb ultraviolet (UV) radiation, and hence significantly reduces the mechanical property loss of the PA6 composite after UV aging. The tensile strength of the aged PA6/7 wt%PhA-MEL-MWCNTs composite sample only decreased by 18.1%, which was significantly lower than the loss rate of the control aged PA6 sample (62.5%). This protocol provides a new opportunity for fabricating long-life flame retardant polyamide composites.
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•PhA-MEL-MWCNTs was fabricated by grafting melamine and phytic acid on MWCNTs.•PhA-MEL-MWCNTs improved flame retardancy and light aging resistance of PA6.•The melt dripping of PA6 was eliminated by 7% PhA-MEL-MWCNTs.•The mechanical loss of PA6 after UV aging was reduced by PhA-MEL-MWCNTs.•The potential danger of PA6 in dairy usage was reduced.
Bu araştırmada, poliamid 6 (PA 6) matris içerisine katı yağlayıcı olarak grafit (G) ve vaks (V) ilave edilerek elde edilen kompozitlerin kuru kayma şartları altındaki tribolojik özellikleri ...incelenmiştir. PA 6/grafit/vaks polimer karışımları ikiz vidalı ekstruderde hazırlanmıştır. Araştırmada kullanılan numuneler enjeksiyonda kalıplama yöntemi ile üretilmiştir. Aşınma deneyleri, ASTM G99’a uygun olarak disk üzerinde pim aşınma cihazında gerçekleştirilmiştir. Deneyler 50N ve 100N aşındırma yükü altında 0,4 m/s, 0,8 m/s ve 1,2 m/s kayma hızında ve 4000m kayma mesafesinde gerçekleştirilmiştir. PA 6 matris içerisine ilave edilen katı yağlayıcılar (grafit, vaks) sayesinde sürtünme katsayısı ve aşınma oranında azalma olduğu görülmüştür. Deney sırasında pim üzerinde yapılan kayma yolu sıcaklık ölçümlerinde PA 6/vaks kompozitinin daha az ısındığı gözlemlenmiştir. Ayrıca PA 6/grafit/vaks kompozitlerin aşınma yüzeylerinin mikro-yapıları SEM yardımı ile incelenmiştir.
•RP, MgO, EG enhance PA6 thermal stability without affecting Tg or crystalline fraction.•Monomer conversion remains high (97%) with no significant impact from FRs.•RP and MgO with EG achieved ...synergistic effects due to different mechanisms.•0.5 mm PA6/5%MgO/5%EGES100 coating reduced the composite pHRR by 27% and THR by 37%.•FRs formed a stable charred layer on the composites and increased the residual mass.
Continuous fibre-reinforced polyamide 6 (PA6) composites are predominantly prepared by anionic ring-opening polymerisation of low viscosity ε-caprolactam monomer. PA6 melts easily when exposed to flames, which can lead to rapid fire spread due to dripping. For this reason, the use of flame retardants is necessary. We investigated the effects of magnesium oxide (MgO), red phosphorus (RP), and expandable graphite (EG) on the glass transition temperature, crystalline fraction, and thermal stability of PA6. After investigating the flammability properties, we selected the best compositions (MgO and RP combined with EG) and applied them as coatings on carbon fibre-reinforced polyamide 6 composites. A synergistic effect was achieved when RP or MgO were used together with expandable graphite. The 0.5 mm thick coating containing 5% RP and 5% EG reduced the peak heat release rate (pHRR) of the composite by 21% and the total heat release (THR) by 28%, while 5% MgO and 5% EGES100 reduced the pHRR by 27% and the THR by 37%.
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The preparation of bio-composites based on engineering plastic is always restricted by the low thermal stability of lignocellulose. In this study, the thermal stability of lignocellulose was improved ...by boric acid modification. Then, the borated lignocellulose was characterized to analyze the mechanism of involved in the improvement of thermal stability. Furthermore, the untreated and borated lignocellulose was combined with polyamide 6 to produce bio-composites. The effects of lignocellulose content and boric acid modification on the color, thermal stability and mechanical properties of the resulting composites were compared and analyzed. Boric acid protected lignocellulose from thermal degradation, increasing the lightness of the resulting composites. However, boric acid appeared to have a negative effect on the mechanical strength of the resulting composites. In summary, this study demonstrated that bio-composites based on engineering plastic could be prepared by improving the thermal stability of lignocellulose using a boric acid treatment.
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•Bio-composites based on engineering plastic were prepared by improving the thermal stability of lignocellulose.•The thermal stability of lignocellulosic fiber was improved by boric acid modification.•The chemical structure of lignocellulose changed because of the complexation reaction between boric acid and lignocellulose.•Boric acid has a positive effect on the physical properties of the composites.
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