WAXD Results Research Articles

Morphology of impact polypropylene copolymer extruded cast film revealed by confocal Raman imaging.

An impact polypropylene copolymer (IPC), composed of polypropylene (PP) and ethylene-propylene copolymer (EPC), was synthesized through two-stage in-reactor polymerization. A systematic investigation of the crystalline structure, thermal behavior, morphology, and tensile properties of the IPC extruded cast film was conducted. Specifically, the morphology of EPC was obtained by confocal Raman imaging by depicting the spatial distribution of the Raman band located at 1064 cm-1. The EPC phase exhibits fibrous morphology with the long axis aligning along the machine direction (MD). A three-dimensional (3D) heterogeneous structure of the IPC cast film obtained by confocal Raman imaging confirms that the fibrous EPC phase is dispersed in a 3D framework of the PP matrix. The mesomorphic phase in the as-prepared cast film transforms to a stable α-form crystal after annealing at 130 °C, which improves the yield strength but decreases the elongation of the cast film. The WAXD and SAXS results indicate that there is no obvious orientation of the crystallites. Thus, the anisotropy of tensile properties in the MD and transverse directions is closely related to the anisotropic phase morphology at the micrometer scale. The results reveal that the mechanical performances of IPC films are determined by the crystalline structure of the PP matrix and the morphology.

Structural evolution of biodegradable polyglycolide fibers under stress-temperature coupled field and its impact on properties

The properties of polyglycolide (PGA) fibers used as surgical sutures depend on their aggregated state structure. The study investigated the relationship between the structural evolution and macroscopic properties of PGA fibers with low-crystallinity under coupled stress-temperature fields by conducting in-situ WAXD/SAXS, DSC and SEM measurements. The WAXD and SAXS results indicated that the structural evolution during the low-temperature stretching stage primarily relied on stress-induced amorphous molecular chain orientation and the formation of small crystals. The DSC results confirmed that uniaxial stretching enhanced the orientation of amorphous molecular chains, leading to cold crystallization of PGA fibers at lower temperatures. During the heating stretching stage at temperatures of 60–90 °C, numerous crystals were generated through a lamellar insertion mechanism and underwent lateral growth. This is reflected by the crystallinity, crystal orientation, and crystallite sizes increased significantly, while the long period decreased rapidly. The high-temperature stretching stage resulted in fragmentation and recrystallization of lamellar crystals, forming fibrous crystals. Stretching at 110 °C exhibited higher Iq2/Iq1 values than other temperatures, which means that 110 °C is more favorable for the formation of fibrous crystals. Additionally, PGA fibers stretched at 150 °C exhibited the highest crystallinity and crystal orientation, which led to a 440 % increase in tensile strength. Its resistance to degradation has also been significantly improved compared to the original fibers.

Fabricating Well-Dispersed Poly(Vinylidene Fluoride)/Expanded Graphite Composites with High Thermal Conductivity by Melt Mixing with Maleic Anhydride Directly

Maleic anhydride (MA) is introduced to fabricate poly(vinylidene fluoride)/expanded graphite (PVDF/EG) composites via one-step melt mixing. SEM micrographs and WAXD results have demonstrated that the addition of MA helps to exfoliate and disperse the EG well in the PVDF matrix by promoting the mobility of PVDF molecular chains and enhancing the interfacial adhesion between the EG layers and the PVDF. Thus, much higher thermal conductivities are obtained for the PVDF/MA/EG composites compared to the PVDF/EG composites that are lacking MA. For instance, The PVDF/MA/EG composite prepared with a mass ratio of 93:14:7 exhibits a high thermal conductivity of up to 0.73 W/mK. It is 32.7% higher than the thermal conductivity of the PVDF/EG composite that is prepared with a mass ratio of 93:7. Moreover, the introduction of MA leads to an increased melting peak temperature and crystallinity due to an increased nucleation site provided by the uniformly dispersed EG in the PVDF matrix. This study provides an efficient preparation method for PVDF/EG composites with a high thermal conductivity.

Tuning interchain cavity of fluorinated polyimide by DABA for improved gas separation performance

Fluorinated polyimides with biphenyl structure and –CF3 with rigid chain structure exhibit great potential in membrane-based gas separation. However, the comprehensive separation performance of this type polyimides is not competitive as a gas separation material. Structure regulation is of great significance to improve the separation performance of polymer membrane. Few studies systematically investigated structure-property relationships in fluorinated polyimide structure. In this study, carboxylic groups are introduced into a fluorinated polyimide(6FDA-TFMB) via copolymerization with DABA diamine monomer. The hydrogen bond between –CF3 group in TFMB and –COOH group in DABA is proposed to enhance chain segment rigidity and optimize polymer chain arrangement. WAXD results and FFV data indicate that inter-chain cavity of fluorinated polyimide could be finely tuned by adjusting molar ratio of TFMB and DABA in the copolyimide. The resulted copolyimide membranes thus demonstrate tunable gas permeation properties. Gas permeability of 6FDA-TFMB/DABA firstly increases and then decreases, and ideal gas selectivity continuously increases with increasing DABA molar ratio. Among the polyimides, 6FDA-TFMB/DABA(6:4) membrane demonstrated superior separation performance, e.g. CO2 permeability of 135.6 Barrer and CO2/CH4 ideal selectivity of 31.6, surpassing the commercial cellulose acetate and Matrimid membrane. Attributed to the optimized interchain interaction, the 6FDA-TFMB/DABA (6:4) membrane displays an optimized CO2 plasticization resistance and physical aging in comparison with 6FDA-TFMB membranes. This study provides a guideline for controlling and optimize the performance of biphenyl fluorinated polyimide gas separation membrane.

Green-in-green biohybrids as transient biotriboelectric nanogenerators

Green self-powered devices based on biodegradable materials have attracted widespread attention. Here, we propose the construction of the transient biotriboelectric nanogenerator (TENG) using green-in-green bionanocompoites. The green-in-green nanocomposites, cellulose nanocrystal (CNC)/polyhydroxybutyrate (PHB), are prepared with a high-pressure molding method. The CNC promotes the degradation and enhances the dielectric constant of CNC/PHB. It further allows for the significant improvement of the triboelectric output of CNC/PHB-based TENG. The voltage output and current output of CNC/PHB-based TENG are 5.7 and 12.5 times higher than those of pristine PHB-based TENG, respectively. Also, the bio-TENG exhibits admirable signal stability in over 20000 cycles. Despite the high hardness of CNC/PHB, a soft but simple-structured arch sensor is successfully assembled using CNC/PHB-based TENG. It can attain the precise real-time monitoring of various human motions. This study may provide new insights into the design/fabrication of green functional materials, and initiate the next wave of innovations in eco-friendly self-powered devices.

Effects on the crystallization behavior and biocompatibility of poly(LLA-ran-PDO-ran-GA) with poly(d-lactide) as nucleating agents.

The blends of poly(l-lactide acid-p-dioxanone-glycolide) (PLPG) with poly(d-lactide) (PDLA) (PLPG/PDLA) were prepared by a solution-casting method. The effects of PDLA on the properties of the PLPG were studied. DSC and WAXD results confirmed that PLA stereocomplex (sc-PLA) crystals were formed by blending PLLA segments in PLPG with PDLA, and the melting endotherm for both PLLA and sc-PLA relied on PDLA content. The non-isothermal crystallization results indicated that the crystallization process was remarkably accelerated by the addition of PDLA. Meanwhile, the results of isothermal crystallization indicated that the half-time of crystallization decreased with the increase of PDLA content. Besides, the enzymatic degradation behavior of the samples showed that with the increase of PDLA content, the mass loss gradually decreased. Furthermore, TGA and DTG results indicated that the thermal degradation of the samples was a complex process. Moreover, the biocompatibility of the samples was tested by cell culture and using CCK-8 and live/dead staining. Results showed that the samples possessed lower cytotoxicity. Therefore, the PLPG/PDLA blends are promising candidate materials in biomedical applications.

Polyurethane cationomers containing fluorinated soft segments with hydrophobic properties

The synthesis of ecological waterborne polyurethane cationomers containing fluorinated polyol (0–20 wt.%) was successfully performed. FTIR and NMR analysis results confirmed the structure of the obtained polyurethane cationomers and incorporation of fluorinated component into the polyurethane chains. Average molar mass and phase structure of the obtained PU thin films were determined based on GPC, FTIR, WAXD and SEM-EDX results. The obtained cationomers have linear structures with clearly visible microphase separation of soft and hard segment domains; the presence of fluorinated polyol changes the strength of hydrogen bonds and in consequence degree of phase separation. The activation energy of glass transition was calculated based on multi-frequency DSC data. It has been shown that the presence of soft fluorinated segments in the cationomer structure strongly influences the hydrophobic, thermal and mechanical properties of the obtained films.

Squeeze Orientation Reinforcement Effect on Cellulose Nanocrystals/Poly(butylene adipate-co-butylene terephthalate) Composites

Cellulose nanocrystals (CNC)/poly(butylene adipate-co-butylene terephthalate) composites enhanced compatibility with phthalic anhydride were one-step prepared via melt blending. The obtained composites then underwent squeezing treatment in a two-roll milling equipment at a given temperature. CNC/PBAT composites were separated and then tested via FTIR and UV–Vis spectrophotometer. During reactive blending, phthalic anhydride selectively reacts with CNC. Before squeezing, tensile strength of CNC/PBAT composites is weakened with increasing phthalic anhydride content. After squeeze treatment at an extension ratio of 6, tensile strength of CNC/PBAT (3/97) is dramatically increased from 29.6 to 148.0 MPa, which is much higher than that of pristine PBAT 85.0 MPa. SEM and WAXD results show that PBAT crystallinity is increased after orientation, and CNC show an orientation arrangement along force direction in PBAT matrix.

Synthesis and characterisation of main-chain liquid-crystal polyurethanes containing azo group

ABSTRACT In this study, three novel main-chain liquid-crystal polyurethanes based on mesogenic diol 4,4ʹ-bis(6-hydroxyhexoxy)biphenyl (BP6), azo diol 4,4ʹ-bis(6-hydroxyhexyloxy)-azobenzene (BHHAB) and 4,4ʹ-diisocyanato-3,3ʹ-dimethylbiphenyl (DMBDI) were synthesised via polyaddition method. The chemical structure, thermal properties, liquid-crystal behaviour and microstructure were fully characterised by FTIR, 1HNMR, UV spectrum, Differential scanning calorimetry (DSC), Thermogravimetric analyzer (TGA), Polarizing optical microscope (POM) and X-ray diffraction techniques. The resulted polyurethanes showed strong UV absorption at 313 nm ascribed to π–π* transition of azo group. All of the polyurethanes showed multiple transitions on DSC curve, which could be ascribed to crystal, melting and isotropization transitions combined with the POM observation. The thermal degradation of the polymers occurred at much higher temperatures (325–331°C) than the melting ones (144–154°C), making the melt processing feasible. The polyurethane showed semicrystalline structure based on diffraction and DSC results. The obtained polyurethanes exhibited smectic mesophase as verified by variable temperature WAXD results, and the mesophase temperature range was more than 25°C based on the POM observation. The obtained polyurethanes could be potentially used in optical and smart intelligence material area.

Soluble Polyimides Bearing (cis, trans)-Hydrogenated Bisphenol A and (trans, trans)-Hydrogenated Bisphenol A Moieties: Synthesis, Properties and the Conformational Effect

In this work, hydrogenated bisphenol A (HBPA) based dinitro mixed isomers (1a′ and 1a) were synthesized and separated via vacuum distillation under the monitor of DSC and 1H NMR. Corresponding diamines (2a′ and 2a) were separately polycondensed with five commercial dianhydrides via a two-step thermal imidization to obtain PI-(1′-5′) and PI-(1-5). All the polyimides could afford flexible, tough, and transparent films, and most of them were readily soluble not only in common polar solvents like DMAc, but also in low boiling point solvents such as chloroform. 1H NMR spectra of the polyimides demonstrated that HBPA moiety showed no conformation changes during the preparation of polymers. For a given dianhydride, PI-(1-5) exhibited better thermal stability than that of PI-(1′-5′), this can be attributed that the equatorial, equatorial C–O in PI-(1-5) promoted denser and more regular molecular chain stacking, as can be evidenced by the WAXD and geometric optimization results. Additionally, when the dianhydride was ODPA, BPADA or 6FDA, no apparent difference was found in either the transmittance or solubility between two series of polyimides, which could be attributed that twisted and flexible ether linkages, as well as bulky substituents, led to the “already weakened” inter- and intramolecular CT interaction and cohesive force. However, when it came to rigid and stiff dianhydride, e.g., BPDA, PI-3′ took an obvious advantage over PI-3 in transmittance and solubility, which was possibly owed to the larger molecular chain d-spacing imparted by equatorial, axial C–O. An overall investigation of PI-(1′-5′) and PI-(1-5) on aspects of thermal, mechanical, morphological, soluble and optical performance values was carried out, and the conformation effects of HBPA isomers on the properties of two series of polyimides were discussed in detail.

New bio-based copolyesters poly(trimethylene 2,5-thiophenedicarboxylate-co-trimethylene terephthalate): Synthesis, crystallization behavior, thermal and mechanical properties

A series of copolyesters based on poly(trimethylene terephthalate) derived from 2,5-thiophenedicarboxylic acid (TFDCA) have been successfully synthesized by the melting polymerization. Microstructures and molecular weights were characterized by 1H NMR and size exclusion chromatography (SEC), respectively. Meanwhile, thermal properties, crystallization behaviors, and crystal structures were investigated by DSC, TGA, and WAXD. The results confirmed the copolymer compositions were nearly equal to the feed compositions. The weight molecular weights were all higher than 21000 g/mol for all polyesters synthesized. With increasing the TFDCA content, the glass transition temperature decreased slightly due to the weaker rigidity of the thiophene ring. DSC and WAXD results demonstrated that the isodimorphic behavior occurred for poly(trimethylene 2,5-thiophenedicarboxylate-co-trimethyleneterephthalate)s (PTTTFs). When TFDCA content was 25%, PTTTF25 exhibited the moderate tensile strength (53.1 MPa). However, the high elongation at break (396%) was observed due to the β relaxation and strain-induced crystallization.

Surface modification of polyamide nanofiber membranes by polyurethane to simultaneously improve their mechanical strength and hydrophobicity for breathable and waterproof applications

In this work, a simple method was proposed to fabricate robust, breathable and waterproof polymer nanofiber membranes. In a typical process, polyamide-6 (PA-6) electrospun membranes were immersed into polyurethane (PU)/DMF solutions for 24 h, and then taken out and dried. SEM results showed that PA-6 nanofibers in the membranes adhered to each other at the inter-fiber junction points. Moreover, the nanofibers were covered by a thin layer of PU, which was also proved by FTIR results. The DSC and WAXD results suggested that the PU had interacted with the PA-6 at molecular level. Through adhesion bonding, the PA-6 nanofiber membrane was interlinked into a huge network, leading to drastically increment in tensile strength of these membranes (357% that of the original value). Moreover, the PA-6 membranes achieved good waterproof ability after the PU solution treatment. The water contact angle was 135.8°, comparable to that of the poly(vinylidene fluoride) (PVDF) electrospun membrane or fluorinated PU/PU coelectrospun membrane. Interestingly, the PU solution treated PA-6 membranes preserved good breathability. It is a facile and scalable approach to fabricate the robust, breathable and waterproof polymer nanofiber membranes.

Poly(propylene glycol)-b-Polylactide 블렌드 필름의 Stereocomplexation과 기계적 물성에 미치는 Poly(propylene glycol)의 블록 구조와 길이의 영향

Stereocomplex polylactide (scPL) shows better mechanical properties than both poly(L-lactide) (PLL) and poly(D-lactide) (PDL). However, scPL is still brittle. In this work, di- and triblock copolymers of poly(propylene glycol) (PPG) and polylactide (PLL or PDL) were synthesized for the preparation of scPL films. The influences of the block structure, PPG block length and blend ratio on stereocomplexation, film morphology and mechanical properties of the scPL films were investigated. From DSC and WAXD results, the 50/50 wt% blend films exhibited the highest stereocomplexation. Phase separation between the scPL and PPG phases was not found from their SEM images. The tensile stress and elongation at break of the blend films increased with the sterecomplex crystallinities. The longer PPG blocks improved both the stereocomplexation and elongation at break of the blend films. In conclusion, the block structures and PPG block lengths influenced on both the stereocomplexation and mechanical properties of the scPL films.

A novel polypropylene composite filled by kaolin particles with β-nucleation

Kaolin-filled polypropylene (PP) composites generally form α-crystal due to the effect of kaolin with α-nucleation. The transition from α- to β-nucleation of kaolin has been investigated, and a novel kaolin with β-nucleation (β-kaolin) and kaolin-filled PP composites with high β-crystal content were prepared first. The DSC and WAXD results indicated that the β-kaolin exhibits stronger β-nucleating ability than CaPA as β-nucleating agent for PP crystallization. It is found that the β-crystal content has been influenced little by filler contents in β-kaolin-filled PP composites. Mechanical properties and spherulitic morphology of filled PP composites was characterized. The synergistic effect of filler and β-crystal significantly improved impact strength of kaolin-filled PP composites.

Peelable clay/PE nanocomposite seals with ultra-wide peelable heat seal temperature window

Abstract This study shows that the controlled dispersion and distribution of nanoclay in clay/polyethylene (PE) nanocomposites result in peelable sealants with an ultra-wide peelable heat-seal temperature window (ΔTp). Different nanoclays, unmodified montmorillonite (Mt) and organo-modified Mt. (OMt), were examined for their capacity to generate peelable clay/PE nanocomposites in a melt-blending film extrusion process. Clay/PE nanocomposite films containing 6 mass% organoclay (OC) exhibited a cohesive peel behavior with a ΔTp of about 12°C while PE film containing 6 mass% unmodified clay resulted in microcomposite with a lock seal performance. With the same mass% of OC, a much lower peel strength with a significantly broad ΔTp of 45°C was achieved mainly due to the fine dispersion of OMt when PE-grafted-maleic anhydride (PE-g-MA) was used as a compatibilizer. WAXD and TEM results confirmed that a substantial enhancement in the dispersion and distribution of intercalated nanoclays was achieved with PE-g-MA compatibilizer. Finally, an ultra-wide ΔTp of over 100°C was obtained for compatibilized OC/PE nanocomposite sealant containing only 3 wt% OC with partially exfoliated microstructure indicating that the exfoliation of nanoclay is in favor of peelability. The peel fracture mechanics of the clay/PE nanocomposite sealants were examined through T-peel test and SEM imaging. The results showed that the dispersion and distribution of nanoclay along with the interfacial adhesion between nanoclay and matrix are the key factors controlling the peel performance of the sealants.

Facile synthesis of bio-sourced polyurethane- fluorosilane modified TiO2 hybrid coatings for high-performance self cleaning application

In this study, modified Titanium nanoparticles (nTiO2) with 1H,1H,2H,2H–Perfluorooctyltrimethoxysilane(FS). Water contact angle reports the abrupt changes in the water contact angle from unmodified TiO2 to modified TiO2 (8.9 to 153o). Further this was incorporated in to the polyurethane matrix to improve the in situ dispersion of polyurethane–FS-nTiO2 hybrid in a solution containing the castor oil, triethanolamine and isophornediisocyanate (IPDI) prepolymer. The resulting synthesis approach produced a uniformly dispersed TiO2 nanoparticles-polyurethane hybrid. This was confirmed by WAXD and AFM results. The degree of hydrophobicity was increased from 68 to 132°. Mechanical test revealed improved tensile strength of polyurethane with the incorporation of FS-nTiO2 from 4.2 MPa to 8.2 MPa and showed the best self-cleaning properties.

Effect of nanoclay localization on the peel performance of PE based blend nanocomposite sealants

Polyethylene (PE) based clay polymer nanocomposites (CPN) are of great importance to generate peelable seals in packaging industry. This study shows the significant effect of organoclay (OC) localization in PE-based blend sealants on their peel properties, for the first time. Two different immiscible blends composed of PE/ethylene-methyl acrylate copolymer (EMA) and PE/ethylene-methyl acrylate-glycidyl methacrylate terpolymer (EMA-GMA) were examined for their potential to generate peelable seals upon addition of organo-modified montmorillonite (OMt). WAXD results and TEM observations reveal that OC is localized at the interface of PE/EMA phases while it is localized within the dispersed EMA-GMA phase in the PE/EMA-GMA blend, which is in agreement with the thermodynamic predictions. The incorporation of 4 phr OC converts the lock seal behavior of the PE/EMA blend seal to a peelable behavior over a wide peelable heat seal temperature range (over 35°C). In contrast, the OC/PE/EMA-GMA nanocomposite sealant, in which OC is mostly located within the EMA-GMA phase, shows lock seal performance similar to the PE/EMA-GMA neat blend.

Enhanced crystallization kinetics of symmetric poly(l-lactide)/poly(d-lactide) stereocomplex in the presence of nanocrystalline cellulose

In this work, poly(l-lactide)/poly(d-lactide)/nanocrystalline cellulose (PLLA/PDLA/NCC) stereocomplex blends were prepared using a solution blending method. The effect of NCC on the crystallization kinetics of symmetric PLLA/PDLA blend was systematically investigated. The incorporation of NCC significantly enhanced the formation of stereocomplex crystal (sc), as indicated by increasing the crystallization peak temperature and crystallinity of sc from approx. 143 °C and 24% to around 160 °C and 40%, respectively, during the non-isothermal crystallizing upon cooling at 10 °C/min. Meanwhile, the addition of NCC caused no influence on the crystal morphology and crystal form of sc in the PLLA/PDLA blend, as evidenced by the POM and WAXD results. The crystallization kinetics of the PLLA/PDLA/NCC blends was studied in detail by using the Dobreva and Gutzow model, the Avrami-Jeziorny equation and the well-known Avrami model. It was found that NCC showed high nucleating activity in the PLLA/PDLA blend. The half-life time of crystallization of the PLLA/PDLA blend was decreased by ca. 78% at 180 °C after the addition of 0.5 wt% NCC. In addition, POM tests showed that the nuclei density in the PLLA/PDLA blend during isothermally crystallizing at 180 °C was largely increased by the addition of NCC.

Stereocomplexation and mechanical properties of polylactide-b-poly(propylene glycol)-b-polylactide blend films: Effects of polylactide block length and blend ratio

In the present work, poly(propylene glycol) (PPG) was block copolymerized to form polylactide-poly(propylene glycol)-polylactide (PL-PPG-PL) triblock copolymers for preparing flexible stereocomplex PL (scPL) blend films. The scPL blend films were prepared by solution blending of poly(L-lactide)-PPG-poly(L-lactide) (PLL-PPG-PLL) and poly(D-lactide)- PPG-poly(D-lactide) (PDL-PPG-PDL) triblock copolymers before film casting. The influences of PL end-block lengths (2 × 104 and 4 × 104 g/mol) and blend ratios (75/25, 50/50 and 25/75 W/W) on the stereocomplexation and mechanical properties of the blend films were evaluated. From DSC and WAXD results, the 50/50 blend films had complete stereocomplexation. Phase separation between the scPL and PPG phases was not observed from their SEM images. The tensile stress and elongation at break increased with the sterecomplex crystallinities and PL end-block lengths. The PPG middle-blocks enhanced elongation at break of the scPL films. The results showed that the PL-PPG-PL triblock structures did not affect stereocomplexation of the PLL/PDL block blending. In conclusion, the phase compatibility and flexibility of the scPL films were improved by PPG block copolymerization.

Morphological evolution and mechanical property enhancement of natural rubber/polypropylene blend through compatibilization by nanoclay

ABSTRACTNanocomposites of natural rubber (NR)/polypropylene (PP) (80/20 wt %) blends filled with 5 phr pristine clay were prepared by melt‐mixing process. Effects of clay incorporation technique via conventional melt‐mixing (CV) and masterbatch mixing (MB) methods on nanostructure and properties of the blend nanocomposites were investigated. The XRD, SAXS, WAXD, and TEM results showed that the clays in the NR/PP blend nanocomposites were presented in different states of dispersion and were locally existed at the interface between NR and PP as well as dispersed in the NR matrix. The presence of clay caused unique morphological evolution such as fine fibrillar PP domains. The tensile strength was improved over the unfilled NR/PP blends by 53% and 224%, and the storage modulus at 25 °C was increased by 78% and 120% for the NR/PP/clay nanocomposites prepared by CV and MB methods, respectively. Significant improvement in both properties was particularly obtained from the MB method due to finer dispersion fibrillar PP phase in the NR matrix and stronger interfacial adhesion between NR and PP fibers, as suggested from DMA. The oil resistance of blend nanocomposites was also improved over that of the unfilled NR/PP blend, and this property was further progressed by the masterbatch mixing method. © 2016 Wiley Periodicals, Inc. J. Appl. Polym. Sci.2017,134, 44574.