Crystallinity Of Polyamide 6 Research Articles

Fate and effect of Polyamide-6 microplastics in mesophilic and thermophilic anaerobic digestion

Research has demonstrated that depending on the type and concentration, microplastics affect anaerobic digestion (AD). Owing to the high abundance of polyamide-6 (PA6) in wastewater treatment plants and limited understanding of its behavior, this study investigates PA6 microplastics' effect in AD. Biochemical methane potential experiments were performed under mesophilic (35 °C) and thermophilic (55 °C) conditions using PA6 at concentrations from 0 to 200 particles/g total solids (TS). Under both conditions, methane production increased in the highest (200 particles/g TS) PA6-dosed reactors, with thermophilic conditions having a statistically significant effect. Methane yield increased from 403.1 ± 5.3 mL/g VS to 436.6 ± 9.2 mL/g VS under thermophilic and from 332.1 ± 1.5 to 340.6 ± 6.6 mL/g VS under mesophilic conditions for the 200 particles/g TS dose, corresponding to increases of 8.3% and 2.6% respectively. PA6 crystallinity decreased from 32.8% to 27.1% and 26.8%, corresponding to decreases of 17.4% in mesophilic and 18.2% in thermophilic reactors compared to pristine control. Similarly, crystallinity decreased in PA6 microplastics collected from abiotic reactors, with thermophilic conditions showing a greater effect. The carbonyl index (CI) values were similar between biotic and abiotic reactors, but PA6 from all reactors had significantly higher CI than pristine PA6, suggesting abiotic factors also affect carbonyl bonds. Additionally, an increase in average PA6 mass was observed for mesophilic and thermophilic conditions by 22.0 % and 23.0 %, respectively. The study shows that temperature and other abiotic factors, like sludge chemistry, significantly influence the fate and effect of PA6 microplastics in digesters. Including abiotic reactors seems crucial for a full understanding of the impact of microbial and non-microbial factors in microplastic studies in the AD process. Studying the effects of microplastics on AD is only one part of the picture, whereas simultaneously examining their fate in digestion is necessary for a complete understanding.

A mechanistic approach toward understanding the mechanical and rheological properties of polyamide/reclaimed rubber blend containing silane-treated silica

The use of reclaimed tire rubber (RTR) as a rubber toughener for engineering plastics such as polyamide 6 (PA6) is a sustainable route for rubber recycling, and it is essential to determine how surface treatment of silica nanoparticles (NPs) contributes to the modification of the blend properties. Here, a comprehensive mechanistic view based on a knowledge of all the influencing factors including the dispersion state of NPs, NP localization, change in matrix crystallinity, and rheology is presented to understand the properties of PA6/RTR/Silica ternary blends. Using the long-chain silane hexamethyltrimethoxysilane, silica was surface-modified at low, medium, and high levels. The impact strength of PA/RTR exhibited an improvement level of 104 % compared to the PA6 system. The results indicate that the change in matrix crystallinity, which is by itself related to the rheological properties, is the primary factor behind the modification of the mechanical properties by the silica nanoparticles. Mechanical engagement interaction resulting from interpenetration of the silane tails significantly altered the rheology and PA6 crystallinity. A secondary role was also found for the NP state of dispersion and localization.

Injection vs micro-injection molding of nano-particle filled polyamide 6: Moldability and structuring

In this work, the moldability via micro-injection molding (μIM) of nano-filled polyamide 6 (PA6) based systems and the microstructural characteristics of the micro-injected parts were investigated and compared to those observed via traditional injection molding (IM). Two types of nano-fillers, different in nature and geometry, were examined, namely carbon nanotubes and silicate layers. The presence of nano-fillers did not impair the mold replication capability of PA6 in the μIM process. A micro-rib and a standard dumbbell specimen for tensile tests were used as reference micro- and macro-injected part, respectively. Transmission Electron Microscopy, Wide and Small Angle X-ray Scattering and Differential Scanning Calorimetry analyses showed that, due to the different thermomechanical histories during μIM and IM, the micro- and the macro-parts have different microstructures, influenced also by the filler type. Both nano-filler dispersion and PA6 crystallinity were influenced.

Thermal and mechanical properties of polyamide 6/poly(vinyl alcohol) blends with and without peroxides

Polyamide 6 (PA6)/polyvinyl alcohol (PVOH) blends of different compositions (90/10, 80/20, 70/30, 60/40) were prepared using Haake rheomixer. The selected blend compositions (80/20 and 60/40) were modified with peroxides (dicumyl peroxide—DCP and tertiary butyl cumyl peroxide—TBCP). The thermal and mechanical properties of the blends were studied. The thermal stability of blends is found to be intermediate to that of PA6 and PVOH. There is no significant change in thermal stability with the addition of peroxides. The FTIR studies proved good interaction between the components in blend systems. The DSC measurements showed reduction in crystallinity of PA6 with the addition of PVOH. The crystallinity further reduced with the addition of peroxides to the blends, due to the formation of crosslink network. The MFI values decreased with the addition of PVOH and peroxides. The PA6/PVOH blends showed poor mechanical properties, whereas the properties were improved with the addition of peroxides to PA6/PVOH blends.

Effect of hot-press thermal history on joint strength of A5052/Polyamide-6 hybrid structure via a porous layer

Abstract The influence of the joining temperature history on the mechanical behavior of an Al alloy (A5052)/Polyamide-6 (PA6) lap joint was investigated. PA6 is a semi-crystalline thermoplastic and its mechanical behavior depends on its crystalline properties, which are affected by thermal processing. The A5052/PA6 joining process was carried out at 215 °C using a hydraulic hot-press. The temperature was decreased from 215 °C to various pre-set temperatures at a cooling rate of about 2 °C/s followed by air cooling under the application of pressure. The crystallinity of PA6 and strength of the lap joint increased with a decrease in the joining temperature from 215 to 190 °C and remained constant at temperatures below 190 °C. The thermoanalytical examination revealed that the crystallinity increase was caused by slow cooling. The results demonstrated that slow cooling is an effectual approach to improve the bonding strength. The fractography analysis results showed that the fracture mode of PA6 changed from ductile to brittle with an increase in its crystallinity.

Simultaneous study of anionic polymerization of ε-caprolactam and crystallization of polyamide 6 in an isothermal process by in situ WAXS

We directly observed the polymerization and crystallization of polyamide 6 (PA6) via anionic polymerization with a combination of in situ wide-angle X-ray scattering (WAXS), temperature measurements, and real-time visualization. In situ WAXS discriminated polymerization and the crystallization of PA6. The peak temperatures produced by exothermic polymerization and crystallization were identified during the temperature measurements. Visual observations were consistent with the WAXS spectral changes. The WAXS results indicated that the molding process consisted of three stages: (1) polymerization induction, (2) polymerization, and (3) crystallization. We compared the polymerization rate, crystallization rate, and crystallinity at each molding temperature. Both polymerization and crystallization were slow at temperatures below 127 °C. Polymerization was fast at temperatures exceeding 166 °C, but PA6 was gelated, and the crystallization rate and crystallinity were low. In contrast, polymerization was fast at 139, 148, and 155 °C, and crystallization was faster at 148 and 155 °C than at 139 °C. Therefore, the total molding time of PA6 was shorter at 148 and 155 °C than at other temperatures. The crystallinity of PA6 decreased with increasing temperature due to increasing molecular weights. We concluded that molding temperatures between 148 and 155 °C were suitable for providing PA6 with high productivities and good properties. The polymerization and crystallization of polyamide 6 (PA6) via anionic polymerization was observed using a combination of in situ wide-angle X-ray scattering (WAXS), temperature measurement, and real-time visualization at 119–182 °C. In-situ WAXS discriminated between polymerization and the crystallization of PA6. The WAXS results indicated that polymerization was fast at 139–155 °C, and crystallization was fast at 148–155 °C. The crystallinity of PA6 decreased with increasing temperature. We concluded that molding temperatures between 148 and 155 °C were suitable for high productivities of PA6 with good properties.

The Application of a Tri-Functional Epoxy Resin as a Crosslinking Agent in Extruded Polyamide-6 Foam

A tri-functional epoxy resin was used to cross-link polyamide-6 (PA6) during chemical extrusion foam molding and its loading-dependent effect on the melting, crystallization properties, crosslinking degree, and melt strength of PA6 as well as the cell morphology of extruded foam specimens was determined. As the tri-functional epoxy resin loading increased the crystallization and melting temperatures of PA6 decreased whereas the area of the melting peak and crystallinity of PA6 first increased and then decreased. Incorporation of epoxy resin also reduced the PA6 processing temperature. Increased tri-functional epoxy resin loading enhanced melt viscosity, the crosslinking degree and melt strength of PA6. Scanning electron microscopy revealed that the foamability of PA6 was obviously improved by the addition of the epoxy resin.

Toward superior applications of thermoplastic elastomer blends: double Tg increase and improved ductility

AbstractWith the aim of curbing air pollution and addressing climate change, the use of low density thermoplastic elastomers (TPEs) in transportation could be a useful way to lighten the vehicle weight. For that, melt blending of high performance rubber and thermoplastics is an attractive way of preparing high performance TPEs. In this work, several TPEs have been prepared by melt blending of hydrogenated acrylonitrile butadiene rubber (HNBR) with polyamide 6 (PA6), adding different amounts of carboxylated HNBR (XHNBR) as compatibilizer: 40/60/0, 40/42/18, 40/30/30 and 40/18/42 (PA6/HNBR/XHNBR). The resulting blends were investigated using melt rheological measurements, morphological observations (scanning electron microscopy and polarized optical microscopy), dynamic mechanical analysis, differential scanning calorimetry analysis and mechanical tests. A biphasic morphology was noted for all TPEs. An increase in XHNBR amount changes the morphology from dispersed to co‐continuous. This evolution is explained by the change in the melt rheological properties of the HNBR/XHNBR rubber phase. Moreover, the introduction of 42% XHNBR resulted in an increase in the glass transition temperature of both rubber and PA6 phases. This double Tg increase phenomenon was attributed to the interfacial interactions between the carboxyl groups in XHNBR and the amine end groups in PA6. Additionally, thermal analysis revealed a reduced crystallinity of PA6 in the blend, which corresponds to enhanced interfacial interactions. The interfacial adhesion and the co‐continuous morphology resulted in an improved ductility. This study reveals the possibility of obtaining TPE blends with tunable thermal and mechanical properties by controlling both interfacial interactions and morphology. © 2019 Society of Chemical Industry

Influence of electron-induced reactive processing on structure, morphology and nano-mechanical properties of polyamide 6/fluoroelastomer blends

Electron-induced reactive processing (EIReP) is a sustainable and energy effective processing technology to modify polymeric materials in the molten state by its spatial and temporal precise energy input. In the present research, the influence of EIReP on nano-mechanical properties of polyamide 6 (PA6)/fluoroelastomer (FKM) blends (50/50 w/w) was successfully explored using advanced PeakForce quantitative nano-mechanical mapping (PF QNM) atomic force microscopy (AFM) technique. In addition, the influence of EIReP on long period of PA6 lamellae and its crystallinity in the blends was studied using small- and wide-angle X-ray scattering (SAXS and WAXS). The AFM based DMT (Derjaguin-Muller-Toporov) moduli of the matrix phase (PA6) and the dispersed phase (FKM) were found to increase, whereas, adhesion force, dissipation energy and deformation of both phases decreased with increasing dose (12.5–25 kGy). Besides of the different crystallinity of PA6 in blends compared to pure PA6, WAXS experiments have demonstrated that the unit cell dimension c-axis of PA6 was sensitive to the melt blending and EIReP. SAXS provided information about the lamellar morphology of the blend component PA6. Variations in the long period of the PA6 lamellae could be assigned to parameters of melt blending and EIReP (dose) and were correlated with the interaction parameter of the phase components and the crystallinity of the blends. PF QNM AFM and X-ray scattering studies established the relationship between the nanoscale phase structure and properties of EIReP modified rubber-plastic blends.

Improvement of dry sliding tribological properties of polyamide 6 using diamond nanoparticles

In the present study, it was revealed that incorporation of nanodiamond containing carboxylic group (ND-COOH) decreased considerably specific wear rate (∼30%) and COF (∼60%) of polyamide 6 (PA6) at 1 wt% loading. Compared with ND-COOH, amino functionalized ND enhanced further wear performance of PA6 which was associated with its finer dispersion as well as greater influence on the improvement of mechanical properties, toughness and crystallinity of PA6. Surface temperature increment caused by frictional heat was in close agreement with COF and wear characteristics of the samples. Optical microscopy images revealed that NDs promote the abrasive wear mechanism in PA6/ND composites.

Morphological and mechanical properties of polyamide 6/nanodiamond composites prepared by melt mixing: effect of surface functionality of nanodiamond

AbstractSurface chemistry of as‐received nanodiamond (ND) was first tailored by dry thermal oxidation to obtain carboxylated ND (ND‐COOH) and by wet chemistry to obtain ethylenediamine‐functionalized ND (ND‐EDA). Then, the surface‐functionalized ND particles were dispersed in polyamide 6 (PA6) using the melt‐mixing method. Transmission optical and scanning electron microscopies indicated a fine dispersion at low nanodiamond concentrations, e.g. 0.25 wt%, particularly with ND‐EDA. Differential scanning calorimetry revealed that ND‐EDA favoured the α‐phase crystal and enhanced the degree of crystallinity of PA6. Experimental data indicated that ND‐EDA had considerably improved tensile properties at low concentration of 0.25 wt% compared to ND‐COOH, which was correlated to the fine dispersion and stronger and thicker interphase in the case of ND‐EDA. It was also found that the toughness of PA6 was improved on incorporation of ND‐EDA due to development of microcracking and crazing. © 2016 Society of Chemical Industry

Effect of halloysite nanotubes on thermal and flame retardant properties of polyamide 6/melamine cyanurate composites

In this study, polyamide 6 (PA6) with various contents of halloysite nanotubes (HNTs) and melamine cyanurate (MCA) were prepared by a twin-screw extruder. The flame retardant and physical properties of PA6 composites were examined. X-ray diffraction (XRD) patterns of PA6/HNTs and PA6/MCA/HNTs composites showed that HNTs as a nanoscale material dispersed in PA6 whether with MCA or not. Thermo gravimetric analyzer (TGA) results showed the presence of HNTs can improve thermal stability of PA6 and PA6/MCA composites. The incorporation of HNTs seemed to result the increase of crystallinity of PA6 and PA6/MCA composites from the differential scanning calorimetry (DSC) results. The combined of HNTs and MCA that leads to further improvements limiting oxygen index (LOI) value of PA6 to 31.7% exerted a positive effect on flame retardancy of PA6. What's more, some mechanical enhancements of PA6 with adding of HNTs were achieved and HNTs also made the tensile properties of PA6/MCA composites improved. POLYM. COMPOS., 36:892–896, 2015. © 2014 Society of Plastics Engineers

Morphology and Crystallization in Polystyrene/polyamide 6 Blends: Influence of a Reactive Compatibilizer and Nano-TiO2

A polystyrene (PS)/polyamide 6 (PA6) (70/30, weight ratio) blend in the presence of terminal malic anhydride functionalized PS (FPS) and nano-TiO2 were prepared using a meltmixing technique. The morphology of the blend was characterized by scanning electron microscopy (SEM) and transmission electron microscopy (TEM). The crystallization behavior of the PA6 phase in the blend was studied using DSC techniques. The results showed that by adding 7.5 phr nano-TiO2, the size of the dispersed PA6 domains was dramatically decreased; An additional 1.5 phr FPS to the PS/PA6/TiO2 blend, for reactive blending, caused the size of the dispersed PA6 domain to become even smaller and more uniform, and a weak, broad crystallization exotherm of PA6 was observed. However, the degree of crystallinity of PA6 in PS/PA6/TiO2/FPS blend was sharply increased.

Obtenção e Caracterização de Membranas Obtidas a Partir de Blendas Poliméricas de Poliamida 6

A mistura de polimeros diferentes possibilita a obtencao de novos materiais com propriedades, na maioria das vezes superiores as dos componentes puros. Essa mistura vem sendo utilizada e aplicada na obtencao de membranas com intuito de melhorar as propriedades de barreira para que se possa separar duas fases restringindo total ou parcialmente o transporte de uma ou varias especies quimicas presentes. Neste trabalho, membranas polimericas foram obtidas a partir de blendas de poliamida 6 (PA6), polipropileno (PP) e compatibilizantes pelo metodo de inversao de fases, com a finalidade de serem utilizadas em processos de separacao, purificacao, fracionamento e contracao. Estas foram estudadas por difracao de Raios-X (DRX), calorimetria exploratoria diferencial (DSC) e microscopia eletronica de varredura (MEV). Os resultados de DRX evidenciaram a presenca dos picos caracteristicos de reflexao da PA6, PP e dos compatibilizantes. Por DSC, observou-se que a presenca do compatibilizante nao promoveu alteracoes significativas na cristalinidade da PA6. Por meio das fotomicrografias de MEV, visualizou-se a obtencao de membranas microporosas assimetricas, como tambem percebeu-se que a presenca da segunda fase na PA6 modificou a morfologia das membranas.

Stress-accelerated photothermal oxidative aging behavior of polyamide 6

The long-term stress-accelerated photothermal oxidative aging behavior of polyamide 6 (PA6) was studied in terms of the creep behavior, mechanical properties, chemical structure, crystallization, and orientation behavior. It was found that the creep deformation of PA6 under stress with ultraviolet (UV) irradiation was lower than that of the sample aging without UV irradiation. Due to stress-induced orientation, the tensile strength of PA6 aging under stress was higher than that of the sample aging without stress. For samples aging with stress, the variation in the content of gel tended to slow down, and the reduced viscosity was lower than that of the sample aging without stress. The oxidation of PA6 can be inhibited by orientation, leading to a relatively low content of carboxylic group; however, stress would accelerate the degradation of PA6, resulting in the strengthening of UV absorption. A decrease in crystallinity of PA6 after aging was observed, which was generated by chain scission in crystalline region and the cross-linking of PA6. Stress would accelerate the degradation of PA6, resulting in further decrease in crystallinity. The orientation factor increased obviously in the case of PA6 aged with stress indicating that a clear orientation of molecules induced by stress formed.

Outdoor weathering of polyamide and polyester ropes used in fall arrest equipment

ABSTRACTIn this work, the effect of natural climatic aging on two ropes made from polyamide 6 (PA6) and poly(ethylene terephthalate) (PET) was evaluated. Samples of rope from both materials underwent a continuous outdoor aging treatment spanning 6 months in Montreal's weather. Tensile tests carried out on aged PA6 ropes showed an increase in ultimate strain and a decrease in breaking force when compared with as‐received values, while PET ropes exhibited a slight increase in ultimate strain as their breaking force remained unchanged. FTIR analyses of aged PET samples revealed a new absorption band in the hydroxyl region ascribed to the OH stretching vibrations of carboxylic acid end groups. FTIR quantitative analyses of the absorption bands in the carbonyl region of aged PA6 spectra displayed an increase in intensity that indicates the occurrence of chemical degradation reactions. The degree of crystallinity of PA6, calculated from differential scanning calorimetry data, was found to increase after the weathering treatment, a result confirmed by X‐ray diffraction analyses. The higher crystalline fraction is believed to entail an increase in the density of PA6 fibers, which give rise to the length reduction seen in PA6 ropes after the aging treatment. © 2013 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 130: 3058–3065, 2013

Study on the Influence of Crystal Structures on the Performance of Low-Melting Polyamide 6

In this article, the effects of crystal structures on polyamide 6(PA6) and low melting point polyamide 6(LPA6) were studied. After heat treatment, the crystal structures of PA6 and LPA6 changed. With the increase of annealed temperature, the crystallinity of PA6 and LPA6 increased and a γ-α crystal transformation occurred, the tensile and flexural properties of the both polyamide 6 increased, especially for LPA6. The Vicat softening temperature of LPA6 increased significantly while the Vicat softening temperature of PA6 decreased slightly.

Role of carboxylic acid functionalized single walled carbon nanotubes in polyamide 6/poly(methyl methacrylate) blend

AbstractThe nanocomposite of polyamide 6 (PA6)/poly(methyl methacrylate) (PMMA)/carboxylic acid functionalized single walled carbon nanotubes (SWCNTs‐COOH) was prepared in a weight ratio of 49.5/49.5/1 at 230°C by using melt‐mixing method. The PA6/PMMA blend with weight ratio of 50/50 served as reference. The Fourier transform infrared analysis of nanocomposite shows the occurrence of hydrogen‐bonding interactions among PA6, PMMA, and SWCNTs‐COOH. Thermal studies of nanocomposite exhibited higher thermal stability and increased crystallinity of PA6 in nanocomposite compared to the blend. The X‐ray diffraction curve of nanocomposite indicates that the rich αII phase of PA6 was higher compare to the blend. The scanning electron microscope analysis of nanocomposite confirmed that PMMA exhibited as a uniform dispersion and existed as co‐continuous phase morphology in a continuous phase of PA6 compared to the blend. Furthermore, the obtained results suggest that the incorporation of SWCNTs‐COOH into the PA6/PMMA blend enhances the compatibility as a compatibilizer between the two polymer components. POLYM. ENG. SCI., 2013. © 2012 Society of Plastics Engineers

The effect of thermal history of polyamide 6 on the crystallization and melting behavior of β-nucleated polypropylene/polyamide 6 blends

It has been proved that the effect of amorphous polymer as the second component on the β-nucleating effect of β-nucleated isotactic polypropylene (iPP) blends was less than that of the crystalline polymers. We guess that it is the crystallinity of the second component that affects the β-nucleating effect. In order to prove this hypothesis, the blends of β-nucleated iPP and polyamide 6 (PA6) were prepared by melt compounding in this study. Cooling rate, crystallization temperature, crystallization time, annealing temperature and annealing time were used to control the crystallinity of PA6 phase, and the effect of PA6 crystallinity on the crystallization and melting behavior was studied, in turn its effect on the β-nucleating effect of iPP phase was explored. The results indicated that β crystal content markedly decreased with the increase of PA6 crystallinity, which proved that PA6 crystallinity controls the α-nucleating effect and suppresses the β-nucleating effect of the β-nucleating agent in the β-nucleated iPP blends, leading to a significant decrease in β crystal content. Therefore, decreasing the crystallinity of the second component in the β-nucleated iPP blends is a feasible method to weaken α-nucleating effect of the second component and an effective way to obtain β-nucleated iPP blend with high β crystal content.

Stress photo‐oxidative aging behaviour of polyamide 6

AbstractThe long‐term stress accelerating aging behaviour of polyamide 6 (PA6) was studied by exposure to UV irradiation. The aging behaviour and mechanism were investigated in terms of creep behaviour, mechanical properties, chemical structure, crystallization and orientation behaviour. It was found that the creep deformation of PA6 under stress/UV irradiation was lower than that of the sample aging only under stress, resulting from crosslinking and low mobility of molecules under UV irradiation. The tensile strength of PA6 under stress and stress/UV irradiation substantially increased at the primary aging stage due to stress‐induced molecular orientation. The oxidation of PA6 may also be inhibited by orientation, leading to a relatively low content of carboxylic groups. Under UV irradiation, stress accelerates the degradation of PA6, resulting in strengthening UV absorption due to formation of isolated carbonyl groups. The melt temperature and crystallinity both showed an increase with time, which were much higher for the sample aged under stress/UV irradiation than for that aged only under UV irradiation. Wide‐angle X‐ray diffraction analysis also showed that the orientation factor and crystallinity of PA6 increased with aging time before 16 days, indicating a clear orientation and crystallization of molecules induced by stress. The UV‐induced crosslinking reduced the mobility of PA6 chains, resulting in a lower crystallinity and orientation factor of the sample aged under stress/UV irradiation compared with that under stress aging only. Copyright © 2011 Society of Chemical Industry