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2019 Volume 50 Issue 8
2019, 50(8):
Abstract:
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2019, 50(8): 764-774
doi: 10.11777/j.issn1000-3304.2019.19069
Abstract:
Benefiting from intensive size effect and surface effect arising from thin fibers, micro/nano-fibrous membranes exhibit many fascinating properties and have become a hot spot and leading edge in the fiber materials. Among the existing processing approaches for micro/nano-fibers, electrospinning has proven to be one of the most effective and promising method due to its integrated characteristics, including broad availability to varieties of polymers, adjustable porous structure, and superior technological convergence. In recent years, our research group have endeavored systematic researches on the controllable fabrication and applications of electrospun micro/nano-fibrous materials, especially in the terms of ultra-thin nanonets, compactly bonded membranes and porous fibrous aerogels. This review mainly puts focus on the formation mechanisms and applications of these distinctive micro/nano-fibrous materials, which are summarized as follows. Firstly, the two-dimensional nanonets with extremely small diameters (< 20 nm) are fabricated by a novel electrospinning/netting technique, and the deformation-phase transition of the charged jets/droplets from polymer solution during the period is also revealed, which have broken the bottleneck of the thinning on diameter of electrospun fibers. And the novel nanonets demonstrate lower air resistance due to the slip flow of air molecules on the periphery of nanofibers, holding great promise as an exceptional candidate for air filtration. Secondly, compactly bonded membranes with stable porous structures are constructed directly through the regulation of the relative humidity, and the effects of relative humidity on electrospinning jet stretching and solidification are investigated. Additionally, hydrophobicly modified compactly bonded membranes demonstrate excellent waterproofness and breathability, thus implying their potential application in selective separation of gas-liquid medium. Thirdly, the ultralight polymeric micro/nano-fibrous aerogels with hierarchical cellular structure and superelasticity are prepared via a novel three-dimensional fibrous framework reconstruction method, which exhibit the integrated properties of extremely low density (minimum of 0.12 mg/cm3), super recyclable compressibility and multifunctionality of combining the thermal insulation, sound absorption, emulsion separation and elasticity-responsive electric conduction. The future perspectives of micro/nano-fibrous materials were also given at the end of this review.
Benefiting from intensive size effect and surface effect arising from thin fibers, micro/nano-fibrous membranes exhibit many fascinating properties and have become a hot spot and leading edge in the fiber materials. Among the existing processing approaches for micro/nano-fibers, electrospinning has proven to be one of the most effective and promising method due to its integrated characteristics, including broad availability to varieties of polymers, adjustable porous structure, and superior technological convergence. In recent years, our research group have endeavored systematic researches on the controllable fabrication and applications of electrospun micro/nano-fibrous materials, especially in the terms of ultra-thin nanonets, compactly bonded membranes and porous fibrous aerogels. This review mainly puts focus on the formation mechanisms and applications of these distinctive micro/nano-fibrous materials, which are summarized as follows. Firstly, the two-dimensional nanonets with extremely small diameters (< 20 nm) are fabricated by a novel electrospinning/netting technique, and the deformation-phase transition of the charged jets/droplets from polymer solution during the period is also revealed, which have broken the bottleneck of the thinning on diameter of electrospun fibers. And the novel nanonets demonstrate lower air resistance due to the slip flow of air molecules on the periphery of nanofibers, holding great promise as an exceptional candidate for air filtration. Secondly, compactly bonded membranes with stable porous structures are constructed directly through the regulation of the relative humidity, and the effects of relative humidity on electrospinning jet stretching and solidification are investigated. Additionally, hydrophobicly modified compactly bonded membranes demonstrate excellent waterproofness and breathability, thus implying their potential application in selective separation of gas-liquid medium. Thirdly, the ultralight polymeric micro/nano-fibrous aerogels with hierarchical cellular structure and superelasticity are prepared via a novel three-dimensional fibrous framework reconstruction method, which exhibit the integrated properties of extremely low density (minimum of 0.12 mg/cm3), super recyclable compressibility and multifunctionality of combining the thermal insulation, sound absorption, emulsion separation and elasticity-responsive electric conduction. The future perspectives of micro/nano-fibrous materials were also given at the end of this review.
2019, 50(8): 775-807
doi: 10.11777/j.issn1000-3304.2019.19062
Abstract:
Conjugated polymers have attracted much attention due to their unique electronic properties and solution processing methods. The rigid and planar conformational backbone manifests extended π-system and the flexible alkyl chain assures the sufficient solubility, which contribute to their tuneable physical and chemical properties and increase the tolerance of film forming and mechanical flexibility. In general, the orthogonal design of functional fragments for conjugated polymers make it accessible for π-stacking of conjugated segments and lamellar stacking of interchain interactions. Short-range aggregates or long-range microcrystals would be selectively and/or successively formed by controlling their chemical structures and processing conditions. Such stacking structure in the phase-separated domain is crucial to the high efficient performance of bulk heterojunction solar cells. The aggregation structure of some typical conjugated polymers has recently been reviewed with a view to providing reference for the development of optoelectrics in this study. Here, D-A copolymers based on oligothiophene, dithiophene, benzothiophene and thiophene derivatives, two-dimensional conjugated polymers and block copolymers are introduced in detail. The aggregation structure of a series of conjugated polymers is systematically summarized by using the different processing techniques, such as selective counterpart components, treating solvents and annealing temperature. In addition, the intrinsic motivation of the controllable aggregation structure is discussed from the aspects of molecular weight and side chain groups.
Conjugated polymers have attracted much attention due to their unique electronic properties and solution processing methods. The rigid and planar conformational backbone manifests extended π-system and the flexible alkyl chain assures the sufficient solubility, which contribute to their tuneable physical and chemical properties and increase the tolerance of film forming and mechanical flexibility. In general, the orthogonal design of functional fragments for conjugated polymers make it accessible for π-stacking of conjugated segments and lamellar stacking of interchain interactions. Short-range aggregates or long-range microcrystals would be selectively and/or successively formed by controlling their chemical structures and processing conditions. Such stacking structure in the phase-separated domain is crucial to the high efficient performance of bulk heterojunction solar cells. The aggregation structure of some typical conjugated polymers has recently been reviewed with a view to providing reference for the development of optoelectrics in this study. Here, D-A copolymers based on oligothiophene, dithiophene, benzothiophene and thiophene derivatives, two-dimensional conjugated polymers and block copolymers are introduced in detail. The aggregation structure of a series of conjugated polymers is systematically summarized by using the different processing techniques, such as selective counterpart components, treating solvents and annealing temperature. In addition, the intrinsic motivation of the controllable aggregation structure is discussed from the aspects of molecular weight and side chain groups.
2019, 50(8): 808-815
doi: 10.11777/j.issn1000-3304.2019.19026
Abstract:
Polymeric vesicles have important applications in biomedicine, nuclear magnetic imaging, nanoreactors, and catalyst fields. Amphiphiic block copolymer nanoparticles with different morphologies (such as vesicles and spheres), sizes and surface chemical properties have been successfully prepared by reversible addition-fragmentation chain transfer (RAFT) polymerization-induced self-assembly (PISA). Generally, it is difficult for researchers to obtain pure vesicles with different sizes. In this study, we report an efficient approach to produce block copolymers vesicles by PISA. A one-pot, facile method for the synthesis of nano-objects composed of amphiphilic poly(4-vinylpyridine)-b-poly(4-vinylpyridine-r-styrene) block copolymer, P4VP-b-P(4VP-r-St), is introduced by P4VP trithiocarbonate macro-RAFT agent mediated dispersion copolymerization of 4VP and St in ethanol/water mixture. It is found that the morphology of P4VP-b-P(4VP-r-St) diblock copolymer nano-objects like spherical micelles, worms, and vesicles can be easily tuned either by changing the degree of polymerization of the random P(4VP-r-St) block, the amount of 4VP comonomer, solvent composition and the ratio of the degree of polymerization of PSt and P4VP segments. Among them, by adding a small amount of 4VP comonomer during the dispersion RAFT polymerization of St, the final morphology of the block copolymer can be greatly affected, pure vesicle can be formed and the size can be adjusted more effectively. Compared with the dispersion RAFT polymerization of St, the advantage of the dispersion RAFT copolymerization by utilizing residual solvophilic monomer to tune the block copolymer morphology is demonstrated. It is believed to be a novel, convenient and efficient protocol for the control of the morphology and size of the block copolymer nano-objects fabricated by PISA. The polymerization shows characteristic features of " living”/controlled radical polymerization and the experimental results are confirmed by gel permeation chromatography (GPC), dynamic light scattering (DLS), transmission electron microscopy (TEM) and 1H-NMR. Due to diverse potential applications of polymer vesicles, the results of this study are of great importance for the theoretical design and application of PISA strategies.
Polymeric vesicles have important applications in biomedicine, nuclear magnetic imaging, nanoreactors, and catalyst fields. Amphiphiic block copolymer nanoparticles with different morphologies (such as vesicles and spheres), sizes and surface chemical properties have been successfully prepared by reversible addition-fragmentation chain transfer (RAFT) polymerization-induced self-assembly (PISA). Generally, it is difficult for researchers to obtain pure vesicles with different sizes. In this study, we report an efficient approach to produce block copolymers vesicles by PISA. A one-pot, facile method for the synthesis of nano-objects composed of amphiphilic poly(4-vinylpyridine)-b-poly(4-vinylpyridine-r-styrene) block copolymer, P4VP-b-P(4VP-r-St), is introduced by P4VP trithiocarbonate macro-RAFT agent mediated dispersion copolymerization of 4VP and St in ethanol/water mixture. It is found that the morphology of P4VP-b-P(4VP-r-St) diblock copolymer nano-objects like spherical micelles, worms, and vesicles can be easily tuned either by changing the degree of polymerization of the random P(4VP-r-St) block, the amount of 4VP comonomer, solvent composition and the ratio of the degree of polymerization of PSt and P4VP segments. Among them, by adding a small amount of 4VP comonomer during the dispersion RAFT polymerization of St, the final morphology of the block copolymer can be greatly affected, pure vesicle can be formed and the size can be adjusted more effectively. Compared with the dispersion RAFT polymerization of St, the advantage of the dispersion RAFT copolymerization by utilizing residual solvophilic monomer to tune the block copolymer morphology is demonstrated. It is believed to be a novel, convenient and efficient protocol for the control of the morphology and size of the block copolymer nano-objects fabricated by PISA. The polymerization shows characteristic features of " living”/controlled radical polymerization and the experimental results are confirmed by gel permeation chromatography (GPC), dynamic light scattering (DLS), transmission electron microscopy (TEM) and 1H-NMR. Due to diverse potential applications of polymer vesicles, the results of this study are of great importance for the theoretical design and application of PISA strategies.
2019, 50(8): 816-825
doi: 10.11777/j.issn1000-3304.2019.19041
Abstract:
Medium molecular weight multi-block copolymers of poly(L-lactic acid) (PLLA) and poly(butylene succinate) (PBS), MMW-mb(PLLA-PBS)s, were controlled-synthesized via melt block copolycondensation (bc-MP) of two macromonomers, i.e. oligo-PLLA (OPLLA) and oligo-PBS (OPBS) with four creatinine (CR)-based organic guanidine (OG) catalysts. The catalytic performance of the four OGs is far superior to that of Sn(Oct)2 in terms of molecular weight (Mw = 14.2 – 28.6 kDa versus 12.9 kDa), apparent yield of synthesized block copolymers (74.15% – 82.02%), as well as the by-product (lactide, LA) yield (1.08% – 6.71% versus 20.7%). Among the OGs, creatinine acetate (CRA) shows the best catalytic performance. 1H-NMR structural characterization of the MMW-mb(PLLA-PBS) synthesized with CRA indicates that the measured molar ratio of the two blocks, fOPLLA/fOPBS, of MMW-mb(PLLA-PBS) is 89.3/10.7, close to the designed value (\begin{document}$\,f\!_{\rm{OPLLA}_0} $\end{document} ![]()
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Medium molecular weight multi-block copolymers of poly(L-lactic acid) (PLLA) and poly(butylene succinate) (PBS), MMW-mb(PLLA-PBS)s, were controlled-synthesized via melt block copolycondensation (bc-MP) of two macromonomers, i.e. oligo-PLLA (OPLLA) and oligo-PBS (OPBS) with four creatinine (CR)-based organic guanidine (OG) catalysts. The catalytic performance of the four OGs is far superior to that of Sn(Oct)2 in terms of molecular weight (Mw = 14.2 – 28.6 kDa versus 12.9 kDa), apparent yield of synthesized block copolymers (74.15% – 82.02%), as well as the by-product (lactide, LA) yield (1.08% – 6.71% versus 20.7%). Among the OGs, creatinine acetate (CRA) shows the best catalytic performance. 1H-NMR structural characterization of the MMW-mb(PLLA-PBS) synthesized with CRA indicates that the measured molar ratio of the two blocks, fOPLLA/fOPBS, of MMW-mb(PLLA-PBS) is 89.3/10.7, close to the designed value (
2019, 50(8): 826-833
doi: 10.11777/j.issn1000-3304.2019.19020
Abstract:
The copolymerization of ethylene with conjugated dienes such as isoprene and butadiene catalyzed by the half-sandwich scandium complexes (C5Me4SiMe3)Sc(CH2C6H4NMe2-o)2 ( 1 ) and (C5Me4SiMe3) Sc(CH2SiMe3)2(THF) ( 2 ) has been detailedly studied. Microstructures and thermal properties of the copolymers obtained were characterized by NMR, GPC and DSC. Results showed that ethylene could be copolymerized with either isoprene or butadiene under 1.01 × 105 Pa of ethylene, and the copolymerization activity both reached up to 105 g polymer molSc−1 h−1 at room temperature. The ethylene-isoprene and ethylene-butadiene copolymers with controllable compositions (ethylene content = 32 mol% − 79 mol%), high molecular weight (Mn = 8.0 × 104 ~ 19.7 × 104), and narrow molecular weight distribution (Mw/Mn = 1.11 − 1.32) were readily obtained by changing the feed ratio of isoprene or butadiene. The structures of catalysts and conjugated dienes could exert significant effects on the stereoselectivity and comonomer distribution sequences in the resulting copolymers. For the copolymerization of ethylene and isoprene, scandium complex 1 afforded multiblock ethylene-isoprene copolymers with different isoprene contents but a predominant 3,4-structure. These copolymers exhibited a glass transition temperature (Tg, about −16 °C) and a melting temperature
The copolymerization of ethylene with conjugated dienes such as isoprene and butadiene catalyzed by the half-sandwich scandium complexes (C5Me4SiMe3)Sc(CH2C6H4NMe2-o)2 ( 1 ) and (C5Me4SiMe3) Sc(CH2SiMe3)2(THF) ( 2 ) has been detailedly studied. Microstructures and thermal properties of the copolymers obtained were characterized by NMR, GPC and DSC. Results showed that ethylene could be copolymerized with either isoprene or butadiene under 1.01 × 105 Pa of ethylene, and the copolymerization activity both reached up to 105 g polymer molSc−1 h−1 at room temperature. The ethylene-isoprene and ethylene-butadiene copolymers with controllable compositions (ethylene content = 32 mol% − 79 mol%), high molecular weight (Mn = 8.0 × 104 ~ 19.7 × 104), and narrow molecular weight distribution (Mw/Mn = 1.11 − 1.32) were readily obtained by changing the feed ratio of isoprene or butadiene. The structures of catalysts and conjugated dienes could exert significant effects on the stereoselectivity and comonomer distribution sequences in the resulting copolymers. For the copolymerization of ethylene and isoprene, scandium complex 1 afforded multiblock ethylene-isoprene copolymers with different isoprene contents but a predominant 3,4-structure. These copolymers exhibited a glass transition temperature (Tg, about −16 °C) and a melting temperature
2019, 50(8): 834-840
doi: 10.11777/j.issn1000-3304.2019.19023
Abstract:
The concentration dependence of chain conformation and disorder-order transition of poly(3-hexylthiophene-2,5-diyl) (P3HT) in toluene solution at room temperature are investigated by multiple characterizations including photoluminescence spectroscopy (PL), UV-Vis absorption spectroscopy (UV-Vis), synchrotron radiation X-ray scattering technique (SAXS), and atomic force microscopy (AFM). The results indicate a critical concentration of ~ 5 mg/mL, at which the interchain interaction and chain aggregation state vary pronouncedly. In the dilute solution (< 5 mg/mL), P3HT chains maintain as independent random coils with negligible interchain interactions despite of regional segmental aggregate formation within the coils as revealed by PL and SAXS measurements. With the solution concentration exceeding the critical value of 5 mg/mL, the chain collapse takes place and the radius of gyration of the molecular chains decreases due to the strengthened π-π couplings among coils. The higher concentration of the solution leads to higher interchain entanglement and more local formation of rod-like segmental aggregates. The amount of the local segment aggregation is found to positively correlated with the concentration, while the radius of gyration and chain conformation exhibit nearly no variation any more at the concentrated solutions. SAXS data display a decreased power law of the concentrated solutions with respect to the dilute solutions, suggesting a lower dimension of the form factor and an improved interchain aggregation in the concentrated solution. This is in good agreement with the UV absorption and PL results. This concentration dependence of the regional chain disorder-order transition in P3HT/toluene solution is further verified to exert great influence on the final crystalline morphologies of the spin-casted films. The segmental aggregated orderings in solution can be effectively transferred to the thin films through namely the " memory effect” during the solution processing, resulting in nanowire structures and higher crystallinity of the films for the higher concentration solution.
The concentration dependence of chain conformation and disorder-order transition of poly(3-hexylthiophene-2,5-diyl) (P3HT) in toluene solution at room temperature are investigated by multiple characterizations including photoluminescence spectroscopy (PL), UV-Vis absorption spectroscopy (UV-Vis), synchrotron radiation X-ray scattering technique (SAXS), and atomic force microscopy (AFM). The results indicate a critical concentration of ~ 5 mg/mL, at which the interchain interaction and chain aggregation state vary pronouncedly. In the dilute solution (< 5 mg/mL), P3HT chains maintain as independent random coils with negligible interchain interactions despite of regional segmental aggregate formation within the coils as revealed by PL and SAXS measurements. With the solution concentration exceeding the critical value of 5 mg/mL, the chain collapse takes place and the radius of gyration of the molecular chains decreases due to the strengthened π-π couplings among coils. The higher concentration of the solution leads to higher interchain entanglement and more local formation of rod-like segmental aggregates. The amount of the local segment aggregation is found to positively correlated with the concentration, while the radius of gyration and chain conformation exhibit nearly no variation any more at the concentrated solutions. SAXS data display a decreased power law of the concentrated solutions with respect to the dilute solutions, suggesting a lower dimension of the form factor and an improved interchain aggregation in the concentrated solution. This is in good agreement with the UV absorption and PL results. This concentration dependence of the regional chain disorder-order transition in P3HT/toluene solution is further verified to exert great influence on the final crystalline morphologies of the spin-casted films. The segmental aggregated orderings in solution can be effectively transferred to the thin films through namely the " memory effect” during the solution processing, resulting in nanowire structures and higher crystallinity of the films for the higher concentration solution.
2019, 50(8): 841-849
doi: 10.11777/j.issn1000-3304.2019.19024
Abstract:
The glass transition, crystallization, and melting behaviors of oligomer poly(L-lactide) (PLLA) confined in anodic aluminum oxide (AAO) nanopores were invesitgated by calorimetry. Compared with the bulk counterpart, PLLA located inside AAO nanopores showed frustrated crystallization during the cooling process, and the crystallization enthalpy gradually decreased with the reduction of pore size. In large nanopores, the crystallization peaks of PLLA nanorods were very close to that of bulk sample, which indicated the predomination of heterogeneous nucleation. Meanwhile, the nonisothermal crystallization results displayed that temperature dependence of nucleation rate of PLLA in nanopores was weaker than that in bulk state. As the diameter of nanopore was smaller than 28 nm, the crystallization peak disappeared. The glass state of PLLA nanorods exhibited double glass transition temperatures (Tgs), the higher Tg attributed to chains in the interfacial adsorbed layer adjacent to pore walls, and the lower Tg belonged to chains in the pore center. The two Tgs showed opposite pore size dependences—the lower one decreased with the reduction of pore size, while the higher one increased. During the heating process, PLLA confined in nanopores showed the pronounced cold crystallization phenomenon, which took place at higher temperatures and the peak was much broader than that of bulk state, which could be ascribed to the supressed nucleation rate, the poor nucleation activity, and the broad nucleation dispersion in PLLA nanorods. Apart form the influence of nucleation, hetergeneous chain mobilities in nanopores also played an important role. Due to the existence of adsorbed layer, surface induced nucleation was hindered. Interestingly, by the nonisothermal crystallization experiments, PLLA chains in the interfacial layer and pore center displayed independent cold crystallization behaviors, and the latter happened at the higher temperatures. Finally, the interfacial effect gradually dominated as the pore size decreased. PLLA crystals formed in small nanopores became unstable, obvious melting-recrystallization phenomena occurred, and the crystallinity and melting temperature of PLLA crystals were lower in smaller nanopores.
The glass transition, crystallization, and melting behaviors of oligomer poly(L-lactide) (PLLA) confined in anodic aluminum oxide (AAO) nanopores were invesitgated by calorimetry. Compared with the bulk counterpart, PLLA located inside AAO nanopores showed frustrated crystallization during the cooling process, and the crystallization enthalpy gradually decreased with the reduction of pore size. In large nanopores, the crystallization peaks of PLLA nanorods were very close to that of bulk sample, which indicated the predomination of heterogeneous nucleation. Meanwhile, the nonisothermal crystallization results displayed that temperature dependence of nucleation rate of PLLA in nanopores was weaker than that in bulk state. As the diameter of nanopore was smaller than 28 nm, the crystallization peak disappeared. The glass state of PLLA nanorods exhibited double glass transition temperatures (Tgs), the higher Tg attributed to chains in the interfacial adsorbed layer adjacent to pore walls, and the lower Tg belonged to chains in the pore center. The two Tgs showed opposite pore size dependences—the lower one decreased with the reduction of pore size, while the higher one increased. During the heating process, PLLA confined in nanopores showed the pronounced cold crystallization phenomenon, which took place at higher temperatures and the peak was much broader than that of bulk state, which could be ascribed to the supressed nucleation rate, the poor nucleation activity, and the broad nucleation dispersion in PLLA nanorods. Apart form the influence of nucleation, hetergeneous chain mobilities in nanopores also played an important role. Due to the existence of adsorbed layer, surface induced nucleation was hindered. Interestingly, by the nonisothermal crystallization experiments, PLLA chains in the interfacial layer and pore center displayed independent cold crystallization behaviors, and the latter happened at the higher temperatures. Finally, the interfacial effect gradually dominated as the pore size decreased. PLLA crystals formed in small nanopores became unstable, obvious melting-recrystallization phenomena occurred, and the crystallinity and melting temperature of PLLA crystals were lower in smaller nanopores.
2019, 50(8): 850-856
doi: 10.11777/j.issn1000-3304.2019.19030
Abstract:
A series of microcellular polypropylene (PP) electrical boxes were fabricated by microcellular injection molding with supercritical nitrogen (Sc-N2) as the physical foaming agent. The effects of higher injection speeds (250 and 290 mm/s) on the cellular structure, unfoamed skin layer thickness, and warpage of the microcellular boxes were quantitatively investigated. According to the simulated gapwise distributions of shear rate, temperature, viscosity, and pressure of PP melt/Sc-N2 solution at the last moment of the filling stage in the molding of the PP boxes, the formation mechanisms of cellular structure and skin layer within the walls of the boxes were analyzed in detail. It was demonstrated that microcellular cells with smaller diameters (less than 90 μm) were developed at the core layer of the boxes. This is mainly because higher injection speeds led to higher pressure drop rate and shear rate, which thereby promoted bubble nucleation. It should be noted that tiny cell area with diameters less than 20 μm and more regular shape appeared near the skin layer of the boxes. This is due to the synthetic effects of higher shear stress combined with lower melt temperature. Along the filling direction, an exponential relationship was found between density and mean diameter of the cells within box sidewall, and the skin layer thickness increased in a nearly linear manner. The latter is mainly attributed to an almost linear decrease in the corresponding surface temperature. Warpages at the open end of the boxes were decreased through increasing the injection speed from 250 mm/s to 290 mm/s. The results demonstrate that more uniform and compact cellular structure as well as thinner unfoamed skin layer is beneficial to lowering the warpage of microcellular injection molded parts. This is worthy of further investigation in the future work.
A series of microcellular polypropylene (PP) electrical boxes were fabricated by microcellular injection molding with supercritical nitrogen (Sc-N2) as the physical foaming agent. The effects of higher injection speeds (250 and 290 mm/s) on the cellular structure, unfoamed skin layer thickness, and warpage of the microcellular boxes were quantitatively investigated. According to the simulated gapwise distributions of shear rate, temperature, viscosity, and pressure of PP melt/Sc-N2 solution at the last moment of the filling stage in the molding of the PP boxes, the formation mechanisms of cellular structure and skin layer within the walls of the boxes were analyzed in detail. It was demonstrated that microcellular cells with smaller diameters (less than 90 μm) were developed at the core layer of the boxes. This is mainly because higher injection speeds led to higher pressure drop rate and shear rate, which thereby promoted bubble nucleation. It should be noted that tiny cell area with diameters less than 20 μm and more regular shape appeared near the skin layer of the boxes. This is due to the synthetic effects of higher shear stress combined with lower melt temperature. Along the filling direction, an exponential relationship was found between density and mean diameter of the cells within box sidewall, and the skin layer thickness increased in a nearly linear manner. The latter is mainly attributed to an almost linear decrease in the corresponding surface temperature. Warpages at the open end of the boxes were decreased through increasing the injection speed from 250 mm/s to 290 mm/s. The results demonstrate that more uniform and compact cellular structure as well as thinner unfoamed skin layer is beneficial to lowering the warpage of microcellular injection molded parts. This is worthy of further investigation in the future work.
2019, 50(8): 857-862
doi: 10.11777/j.issn1000-3304.2019.19032
Abstract:
Poly(acrylic acid) (PAA) and poly(ethylene oxide) (PEO) can form hydrogen-bonded polymer complex. A PAA/PEO homogenous solution can be obtained by adding NaOH into the mixture to restrict the hydrogen bonding between PAA and PEO. First, PAA was dissolved in 20 mL of NaOH aqueous solution and PEO was dissolved in 20 mL of distilled water with the total mass of PAA and PEO of 3.48 g. After stirred for 6 h and centrifuged in the deaeration system at 3500 r/min for 10 min, the mixture was blade coated onto a PTFE plate through an adjustable film applicator with the thickness of 2 mm, and dried in the ambient environment to obtain PAA/PEO films. The effects of film composition and acid treatment on the structures and mechanical properties of the films were studied by Fourier transform infrared spectroscopy (FTIR), differential scanning calorimetry (DSC), wide angle X-ray diffraction (XRD), and mechanical streching machine. The crystallization behavior of PEO and the mechanical properties of the films showed strong dependence on the hydrogen bonding between PAA and PEO. The elongation increased while the tensile strenghth and the Young’s modulus decreased first and then increased with the increasing PEO content in the films. After incubation in a pH = 1 solution for 3 min, the hydrogen bonding between PAA and PEO was enhanced. Compared with the film without acid treatment, the flexibility of the film was greatly enhanced after acid incubation. In particular, Young’s modulus of the film (n(AA):n(EO) = 1:3) before acid treatment was 426 MPa while it declined to 3 MPa after acid incubation. Namely, when the hydrogen bonding between PAA and PEO became weak, PEO would crystallize and the film performed like a plastic material. When the hydrogen bonding between PAA and PEO became strong, the crystallization of PEO was restricted and the film acted as a rubber material.
Poly(acrylic acid) (PAA) and poly(ethylene oxide) (PEO) can form hydrogen-bonded polymer complex. A PAA/PEO homogenous solution can be obtained by adding NaOH into the mixture to restrict the hydrogen bonding between PAA and PEO. First, PAA was dissolved in 20 mL of NaOH aqueous solution and PEO was dissolved in 20 mL of distilled water with the total mass of PAA and PEO of 3.48 g. After stirred for 6 h and centrifuged in the deaeration system at 3500 r/min for 10 min, the mixture was blade coated onto a PTFE plate through an adjustable film applicator with the thickness of 2 mm, and dried in the ambient environment to obtain PAA/PEO films. The effects of film composition and acid treatment on the structures and mechanical properties of the films were studied by Fourier transform infrared spectroscopy (FTIR), differential scanning calorimetry (DSC), wide angle X-ray diffraction (XRD), and mechanical streching machine. The crystallization behavior of PEO and the mechanical properties of the films showed strong dependence on the hydrogen bonding between PAA and PEO. The elongation increased while the tensile strenghth and the Young’s modulus decreased first and then increased with the increasing PEO content in the films. After incubation in a pH = 1 solution for 3 min, the hydrogen bonding between PAA and PEO was enhanced. Compared with the film without acid treatment, the flexibility of the film was greatly enhanced after acid incubation. In particular, Young’s modulus of the film (n(AA):n(EO) = 1:3) before acid treatment was 426 MPa while it declined to 3 MPa after acid incubation. Namely, when the hydrogen bonding between PAA and PEO became weak, PEO would crystallize and the film performed like a plastic material. When the hydrogen bonding between PAA and PEO became strong, the crystallization of PEO was restricted and the film acted as a rubber material.
