Comparation of effectiveness of silicone hydrogel contact lens and hydrogel contact lens in patients after LASEK

AIMTo conduct a comparative study of effectiveness of silicone hydrogel contact lens and hydrogel contact lens, which are used in patients after laser-assisted subepithelial keratomileusis (LASEK).METHODSSixty-three patients (121 eyes) with a spherical equivalent ≤-5.0 D were chosen after undergoing LASEK in 2012 at Guangdong General Hospital. They were randomly divided into 2 groups. The silicone hydrogel group included 32 cases (61 eyes) that wore silicone hydrogel contact lenses for 4-6d after the operation, while the hydrogel group included 31 cases (60 eyes) who wore hydrogel contact lenses for 4-6d after the operation. Patients' self-reported postoperative symptoms (including pain, photophobia, tears, and foreign body sensation) were evaluated. The healing time of the corneal epithelium, the visual acuity of patients without contact lens after epithelial healing, and the incidence of delayed corneal epithelial shedding were also assessed. The follow-up time was 1mo.RESULTSPostoperative symptoms were milder in the silicone hydrogel group than in the hydrogel group. There were significant differences in pain, foreign body sensation, and photophobia between the 2 groups (P<0.05), although there was no significant difference in postoperative tearing (P>0.05). The healing time of the corneal epithelium in the silicone hydrogel lens group was markedly shorter than that in the hydrogel group (4.07±0.25 vs 4.33±0.82d, t=2.43, P=0.02). Visual acuity without contact lenses after healing of the corneal epithelium was better in the silicone hydrogel group compared with the hydrogel group (χ2=7.76, P=0.02). There was no significant difference in the occurrence of delayed corneal epithelial shedding between the 2 groups (P>0.05).CONCLUSIONPatients with LASEK using silicon hydrogel contact lenses had less discomfort and shorter corneal epithelial healing time compared with those using hydrogel contact lenses, suggesting that silicon hydrogel contact lenses may be considered to be a better choice of bandage contact lens after LASEK.

Flexible Polydimethylsiloxane Composite with Multi-Scale Conductive Network for Ultra-Strong Electromagnetic Interference Protection

Highly conductive polymer composites(CPCs) with excellent mechanical flexibility are ideal materials for designing excellent electromagnetic interference(EMI) shielding materials,which can be used for the electromagnetic interference protection of flexible electronic devices.It is extremely urgent to fabricate ultra-strong EMI shielding CPCs with efficient conductive networks.In this paper,a novel silver-plated polylactide short fiber(Ag@PL ASF,AAF) was fabricated and was integrated with carbon nanotubes(CNT) to construct a multi-scale conductive network in polydimethylsiloxane(PDMS) matrix.The multi-scale conductive network endowed the flexible PDMS/AAF/CNT composite with excellent electrical conductivity of 440 S m-1and ultra-strong EMI shielding effectiveness(EMI SE) of up to 113 dB,containing only 5.0 vol% of AAF and 3.0 vol% of CNT(11.1wt% conductive filler content).Due to its excellent flexibility,the composite still showed 94% and 90% retention rates of EMI SE even after subjected to a simulated aging strategy(60℃ for 7 days) and 10,000 bending-releasing cycles.This strategy provides an important guidance for designing excellent EMI shielding materials to protect the workspace,environment and sensitive circuits against radiation for flexible electronic devices.

Hydrogen bond producers in powerful protic ionic liquids for enhancing dissolution of natural cellulose

The manipulation of hydrogen bonding within protic ionic liquids is conducive to conquering the robust hydrogen bonding interactions in cellulose for its effective dissolution,but it is a great challenge to establish the delicate bal-ance of hydrogen bonding network between solvent and cellulose.Herein,we proposed the concept of“hydrogen bond producers”for urea molecules in 1,1,3,3-tetramethylguanidinium methoxyacetate acid([TMGH][MAA])to enhance the dissolution of cellulose.The optimization of physicochemical properties for[TMGH][MAA]solvent as a function of urea concentration revealed a remark-able increase in cellulose solubility from 13%to 17%(w/w)by adding only 0.25 wt%urea,highlighting the efficiency of[TMGH][MAA]as a power-ful solvent for the dissolution of cellulose.The experimental and simulation results verified that the significant improvement on dissolution of cellulose was attributed to the hydrogen bonding interaction of urea molecules with ion pairs and part of free ions,reducing the interference with the active ions bonded to cellulose.Furthermore,the considerable enhancement on compre-hensive properties of regenerated cellulose films demonstrated the effectiveness of[TMGH][MAA]/urea solvent.The concept of“hydrogen bond producers”presented here opens a new avenue for significantly enhancing the dissolu-tion of natural cellulose,promoting the sustainable development in large-scale processing of cellulose.

Investigation of gas content of organic-rich shale:A case study from Lower Permian shale in southern North China Basin,central China

Measuring gas content is an essential step in estimating the commerciality of gas reserves. In this study,eight shale core samples from the Mouye-1 well were measured using a homemade patented gas desorption apparatus to determine their gas contents. Due to the air contamination that is introduced into the desorption canister, a mathematical method was devised to correct the gas quantity and quality.Compared to the chemical compositions of desorbed gas, the chemical compositions of residual gas are somewhat different. In residual gas, carbon dioxide and nitrogen record a slight increase, and propane is first observed. This phenomenon may be related to the exposure time during the transportation of shale samples from the drilling site to the laboratory, as well as the differences in the mass, size and adsorptivity of different gas molecules. In addition to a series of conventional methods, including the USBM direct method and the Amoco Curve Fit(ACF) method, which were used here for lost gas content estimation, a Modified Curve Fit(MCF) method, based on the 'bidisperse' diffusion model, was established to estimate lost gas content. By fitting the ACF and MCF models to gas desorption data, we determined that the MCF method could reasonably describe the gas desorption data over the entire time period, whereas the ACF method failed. The failure of the ACF method to describe the gas desorption process may be related to its restrictive assumption of a single pore size within shale samples. In comparison to the indirect method, this study demonstrates that none of the three methods studied in this investigation(USBM, ACF and MCF) could individually estimate the lost gas contents of all shale samples and that the proportion of free gas relative to total gas has a significant effect on the estimation accuracy of the selected method. When the ratio of free gas to total gas is lower than 45%, the USBM method is the best for estimating the lost gas content, whereas when the ratio ranges from 45% to 75% or is more than 75%, the ACF and MCF methods, are the best options respectively.

Which Patients Should be Administrated Prophylactic Antibacterial Agents? A Study of Bacteriuria or Funguria by Urine Culture Taken From the Renal Pelvis in Children with Ureteropelvic Junction Obstruction

Objective: To detect bacteriuria or funguria by urine culture taken from the renal pelvis directly before Anderson-Hynes pyeloplasty. Methods: 290 patients who underwent Anderson-Hynes pyeloplasty for ureteropelvic junction obstruction (UPJO) were included in a retrospective analysis. Urine was obtained directly before the renal pelvis was opened, and was carried to the laboratory for bacterial culture. Clinical features were analyzed to evaluate risk factors for bacteriuria or funguria by comparing patients whose urine yielded positive cultures to those whose urine cultures were negative for bacteria or yeast. Results: Eighteen patients (6.2%) had positive urine cultures, including six cultures positive for Escherichia coli (E. coli), four for Pseudomonas aeruginosa, three for klebsiella pneumoniae, one for maltophilia monad, one for Enterococcus faecium, one for Candida albicans, one for Candida parapsilosis, and one for yeast not otherwise specified. Bacteriuria or funguria was significantly correlated with four clinical features: fever, urinary urgency, and history of nephrostomy or pyeloplasty. Conclusions: Bacteriuria or funguria was less common in children with UPJO, and the majority of organisms were identified as Escherichia coli, Pseudomonas aeruginosa, or Klebsiella pneumoniae. Prophylactic antibacterial agents were probably necessary in those patients who had signs of urinary tract infection (UTI), or history of nephrostomy or pyeloplasty.

Universal production of functionalized 2D nanomaterials via integrating glucose-assisted mechanochemical exfoliation and cosolvent-intensified sonication exfoliation

Two-dimensional(2D)nanomaterials have aroused immense attention in extensive applications due to their intriguing physical and chemical properties.However,there is a formidable challenge to prepare few-layered and functionalized 2D nanomaterials in an effective and universal way.Herein,we developed an integrated strategy of glucose-assisted mechanochemical exfoliation and cosolvent-intensified sonication exfoliation to effectively exfoliate and functionalize 2D materials.Taking exfoliation of boron nitride(BN)as an example,the production yield and functionalization ratio of BN nanosheets(BNNSs)reached 47.5%and 25.8 wt.%,188%and 16%higher than that of BNNSs without sonication exfoliation,respectively.The introduction of glucose not only augmented the friction force between adjacent BN layers to promote the efficiency of ball-milling-driven exfoliation supported by density functional theory calculation,but also reacted with active edges of BNNSs for functionalization.Afterwards,cosolventintensified sonication exfoliation strongly stabilized exfoliated BNNSs,obviously boosting the exfoliation yield.This proposed method is universal for preparing various 2D nanomaterials like molybdenum disulfide,tungsten disulfide,and graphene nanosheets.The thin plate structure and high functionalization ratio enabled the release of property superiorities of 2D nanomaterials.Our work offers a promising prototype to realize mass production of functionalized 2D nanomaterials.

Carbon aerogel microspheres with in-situ mineralized TiO_(2)for efficient microwave absorption

Carbon aerogels(CAs)have been considered potential microwave absorption(MA)materials because of intrinsic hierarchical porous structure,low density,and excellent heat resistance.However,CAs always required to be ground into micron-scale powder before being used as microwave absorbers,which will inevitably destroy the hierarchical porous structure.Meanwhile,reproducing the optimized CAs powders is difficult.Herein,CAs microspheres with in-situ mineralized TiO_(2)were easily prepared via a sol–gel transition and calcination process.The uniform size of CA microspheres and the loaded TiO_(2)on the skeleton of CA yield great microwave attenuation performance while guaranteeing good impedance matching performance.The obtained TiO_(2)/CA hybrid presented a minimum reflection loss value of−30.2 dB and a broad effective absorption bandwidth(reflection loss below−10 dB)of 6.2 GHz.The low density,MA performance,and controllable particle size make the novel TiO_(2)/CA hybrid promising candidates for MA applications.

Interfacial Banded Transcrystallization of Polyoxymethylene/Poly(butylene succinate) Blends Induced by the Polyamide 6 Fiber

Interfacial crystallization of polyoxymethylene/poly(butylene succinate)blends induced by the polyamide 6(PA6)fiber was investigated.Due to strong heterogeneous nucleating ability,dense nuclei were generated on the surface of the PA6 fiber,which compelled the growth of twisted lamellae perpendicular to the PA6 fiber.As a result,unique interfacial banded transcrystallization was formed,which is rarely found before.Crystallization temperature was dominant in determining the nucleation activity of the PA6 fiber,further affecting the architecture of banded transcrystallization.With the increase of crystallization temperature,the nucleation density decreased to give more growth space for the twisted lamellae around the fiber.The wave-like banded stripes were transformed into fan-like stripes.Accordingly,band spacing and eccentricity respectively showed positive and negative correlation with crystallization temperature.These meaningful results shed light on regulating the architecture of banded crystals in polymer composites.

Fabrication of Highly Anisotropic and Interconnected Porous Scaffolds to Promote Preosteoblast Proliferation for Bone Tissue Engineering

Mimicking the complex structure of natural bone remains a challenge for bone tissue scaffolds.In this study,a novel processing strategy was developed to prepare the bone-like scaffolds that are featured by highly oriented and fully interconnected pores.This type of biomimetic scaffolds was evolved from solid phase stretching of immiscible polycaprolactone(PCL)/poly(ethylene oxide)(PEO)blends with cocontinuous structure and the pore morphology was inherited from selective extraction of water soluble PEO phase.The pore anisotropy was readily tuned by varying the stretching strain without loss of interconnectivity.Significant promotion in preosteoblast proliferation,alkaline phosphatase activity and osteogenic gene expression was observed in the oriented porous scaffolds compared to the isotropic porous counterpart.The oriented architecture provided a topographical cue for aligned growth of preosteoblasts,which activated the Wnt/β-catenin signaling pathway.The proposed strategy enriches the toolbox for the scaffold design and fabrication for bone tissue engineering.

Better Choice:Linear Long Chains Rather than Branched Ones to Improve Mechanical Performance of Polyethylene through Generating Shish-Kebabs

We utilized two structurally different long chains(linear and branched ultra-high molecular weight polyethylene)to reveal the dependence of flow-induced crystallization on long chain architecture,and prepared two bi-disperse systems of 98 wt%short chain and 2 wt%long chain.A flow field was applied to the bi-disperse polyethylene melt by a modified injection-molding machine,known as oscillation shear injection molding(OSIM).For the first time,the structural influence of long chains on flow-induced shish-kebab formation was systematically investigated.For the intermediate layer of OSIM samples,the branched long chains were better than the linear long chains at inducing shish-kebab formation,agreeing with the reported literatures,because the branches can maintain their oriented conformations longer.But unexpectedly,the reverse is the case for the core layer of OSIM samples,where the shear flow was much weaker than the intermediate layer.To understand the unexpected phenomenon,the lifetime of shishes induced by different long chains was compared.Result demonstrated that the linear-induced shishes possessed higher thermal stability than the branched-induced ones so that the linear-induced shishes could survive in the core layer of OSIM samples.Additionally,unlike other methods for flow-induced crystallization,OSIM could create samples for measuring mechanical properties,and thus offer the chance to reveal the relationship between structure and performance.The mechanical results demonstrated that both long chains remarkably enhanced the mechanical properties because of the significant promoting effect of long chains and intense flow fields on shish-kebab formation.However,the linear long chains induced more stable and flawless shishes with higher tensile strength and modulus(80.4 and 1613.5 Mpa,respectively)than the branched ones(74.4 and 1489.3 Mpa).Our research not only helps elucidate the mechanism of shish-kebab formation but also provides a better choice to reinforce polymers by adding long chains with suitable structure.

How the Aggregates Determine Bound Rubber Models in Silicone Rubber? A Contrast Matching Neutron Scattering Study

The correlation between aggregates and bound rubber structures in silicone rubbers(S(phr)) with various silica fractions(ΦSi) has been investigated by contrast matching small-angle neutron scattering(SANS), swelling kinetics, and low-field nuclear magnetic resonance(NMR).Mixed solvents with deuterated cyclohexane fractions of 4.9% and 53.7% were chosen to match the scattering length densities of the matrix(SMP(phr)) and the filler(SMS(phr)), respectively. All the data consistently suggest that:(i) There is a critical threshold ΦSic between 10 and 30 phr;below ΦSic, the isolated aggregates are dominant, while beyond ΦSic, some rubber fraction is trapped among the agglomerate;(ii) ΦSiindependent thicknesses around 7.5 nm(NMR) and 8.6 nm(SANS) suggest that the bound rubber formation is determined by inherent properties of the components, and the power-law around 4.2 suggests an exponential changed gradient density of the bound rubber;(iii) SMS(80) presents a bicontinuous bound rubber with three characteristic lengths of 41, 100, and 234 nm. The expanded correlation length, a 20 nm smaller aggregate sizes suggest that such existent bicontinuous network in dry samples with less ΦSi is kind of impacted by swelling. With the obtained bound rubber models, the reinforcing mechanism of filled silicone rubber is elucidated.

The Crystallization Behavior of Biodegradable Poly(butylene succinate) in the Presence of Organically Modified Clay with a Wide Range of Loadings

The crystallization behavior of poly（butylene succinate） （PBS） nanocomposites with a wide range of contents of clays was revealed. It was of interest to find that the crystallization rate of PBS was accelerated obviously at relatively low contents of clays; while a retarded crystallization kinetics and a decreased crystallinity of PBS were found in the nanocomposites with higher clay contents. Two interplaying effects existed in the nanocomposites, i.e., a suppression effect of clays on nucleation and a templating effect of clays on crystal growth, were clarified to contribute to this intriguing crystallization behavior.

Towards Efficient Electromagnetic Interference Shielding Performance for Polyethylene Composites by Structuring Segregated Carbon Black/Graphite Networks

An electromagnetic interference （EMI） shielding composite based on ultrahigh molecular weight polyethylene （UHMWPE） loaded with economical graphite-carbon black （CB） hybrid fillers was prepared via a green and facile methodology, i.e., high-speed mechanical mixing combined with hot compression thus avoiding the assistance of the intensive ultrasound dispersion in volatile organic solvents. In this composite, the graphite-CB hybrid fillers were selectively distributed in the interfacial regions of UHMWPE domains resulting a typical segregated structure. Thanks to the specific morphology of segregated conductive networks along with the synergetic effect of large-sized graphite flakes and small-sized CB nanoparticles, a low filler loading of 7.7 vol% （15 wt%） yielded the graphite-CB/UHMWPE composites with a satisfactory electrical conductivity of 33.9 S/m and a superior shielding effectiveness of 40.2 dB, manifesting the comparable value of the pricey large-aspect-ratio carbon nanofillers （e.g., carbon nanotubes and graphene nanosheets） based polymer composites. More interestingly, with the addition of 15 wt% graphite-CB （1/3, W/W） hybrid fillers, the tensile strength and elongation at break of the composite reached 25.3 MPa and 126%, respectively; with a remarkable increase of 58.1% and 2420% over the conventional segregated graphite/UHMWPE composites. The mechanical reinforcement could be attributed to the favor of the small-sized CB particles in the polymer molecular diffusion between UHMWPE domains which in tuna provided a stronger interfacial adhesion. This work provides a facile, green and affordable strategy to obtain the polymer composites with high electrical conductivity, efficient EMI shielding, and balanced mechanical performance.

Highly enhanced microwave absorption for carbon nanotube/barium ferrite composite with ultra-low carbon nanotube loading

Barium ferrite(BaFe_(12)O_(19))is considered as potential microwave absorption(MA)material thanks to the large saturation magnetization,high Curie temperature,and excellent chemical stability.The integration of carbon nanotube(CNT)can improve the dielectric loss of BaFe_(12)O_(19)for further enhanced MA perfor-mance,nevertheless,the MA performance is still not desirable because of the poor CNT dispersion in the CNT/BaFe_(12)O_(19)composites,which usually prepared via the ball-milling method,unless high CNT loading was used.Herein,according to the thermal stability of CNT in different atmosphere and the formation mechanism of BaFe_(12)O_(19)from precursor,CNT was introduced in the precursor of BaFe_(12)O_(19)uniformly during auto-ignition process and calcined under different atmosphere.When CNT loading is only 2.0 wt%,the CNT/BaFe_(12)O_(19)composites obtained exhibits a minimum reflection loss(RL_(min))of-43.9 dB and effective bandwidth(with RL<-10 dB)of 3.9 GHz with the thickness of 1.5 mm,which are much supe-rior to-10.2 dB and 2.2 GHz for pure BaFe_(12)O_(19),and-13.6 dB and 2.5 GHz for CNT/BaFe_(12)O_(19)composite prepared by ball-milling method.These results may pave the way to design high-performance BaFe_(12)O_(19)based microwave absorbers.

Facile fabrication of highly durable superhydrophobic strain sensors for subtle human motion detection

Endowing strain sensors with superhydrophobicity is of great importance to guarantee their long-term service under harsh environments(such as wet,acid,alkali and salt atmospheres),whereas,the development of superhydrophobic strain sensors remains a great challenge.Herein,we realized a superhydrophobic and highly sensitive sensor for subtle human motion detection by designing a superhydrophobic and electrically conductive coating on cotton textile,via a facile drop-coating method.The resultant strain sensor showed a large water contact angle of 161.3°and a low sliding angle of 3.8°The superhydrophobic characteristics can keep almost unchanged even after undergoing 1000 peeling cycles,1000 stretchingrelease cycles,and 1000 bending-releasing cycles,revealing its excellent mechanical robustness.High sensitivity with the maximum gage factor of 169 was achieved for the strain sensor under a small strain of0–10%,and the sensing performance also showed well durability.Moreover,our sensor can effectively detect various subtle human physiological signals and body motions even under harsh conditions.These admirable features make the sensor promising applications in wearable electronics,personalized health monitoring,sound recognition,and so on.

Temperature-dependent β-Crystal Growth in Isotactic Polypropylene with β-Nucleating Agent after Shear Flow

In our current work, the effect of the shear temperature on the growth of β-crystal in isotactic polypropylene（iPP） with β-nucleating agent is investigated by means of in situ two-dimensional wide-angle X-ray diffraction（2 D-WAXD）. At low shear temperatures, the formed shear-induced oriented precursors are hard to relax back to random coiled state due to the weak mobility of molecular chains. Therefore, plenty of oriented α-crystals are induced by shear-induced oriented precursors, while β-crystal is greatly depressed. As the shear temperature increases, oriented β-crystal gradually increases along with the decrease of α-crystal. It is deduced that the shear temperature at which the content of β-crystal increases to the（maximum） value found in quiescent crystallization is almost the same as that at which the accelerating effect of flow on crystallization kinetics is completely erased. Our work manifests its significance in regulating β-crystal and thus in the structure and property manipulation of i PP.

Superior Ductile and High-barrier Poly(lactic acid)Films by Constructing Oriented Nanocrystals as Efficient Reinforcement of Chain Entanglement Network and Promising Barrier Wall

It is a daunting task to develop a promising strategy at an industrial scale for simultaneously ameliorating ductility and gas barrier performance of poly(lactic acid)(PLA)films in the application of green packaging.In this work,biaxial stretching and constrained annealing were employed to prepare transparent PLA films with superior ductility and barrier properties.The oriented nano-sized crystals induced by biaxial stretching were developed into regularαform during constrained annealing,which could not only serve as“nano-barrier wall”to impede the diffusion and dissolution of gas molecules,but also strengthen amorphous chain entanglement network as physical crosslink to enhance ductility.As a result,the as-prepared PLA films exhibited an outstanding comprehensive performance with a low oxygen and water vapor permeability coefficient of 0.733×10^(-14) cm^(3)·cm·cm^(-2)·s^(-1)·Pa^(-1) and 3.82×10^(-14) g·cm·cm^(-2)·s^(-1)·Pa^(-1),respectively,outstanding ductility with elongation at break of 66.0%,high yield strength of 84.2 MPa,and good transparency of more than 80%at 550 nm.The new insight in the relationship between microscopic amorphous and crystalline structure and macroscopic performance is conducive to alleviating the intrinsic defects of brittle and insufficient barrier PLA films without the aid of any heterogenous modifiers,facilitating their widespread commercialization in the booming sustainable packaging market.

Insight into the Excellent Tribological Performance of Highly Oriented Poly(phenylene sulfide)

Achieving low friction and wear of poly(phenylene sulfide)(PPS) without using fillers or blending is a challenging task, but one of considerable practical importance. Here we describe how neat PPS with high tribological performance is achieved by manipulating processing parameters(pressure, flow and temperature). The key to achieving high tribological performance is comparatively high molecular chain orientation, realized in neat PPS, at high shear rates and low pressure. The friction coefficient and wear rate are as low as ~0.3 and~10^(-6) mm^(3)·N^(-1)·m^(-1), respectively, which break the record for neat PPS. These values are even better than those for PPS-based blends and comparable to PPS composites. Further studies show, for the first time, that wear rate decreases exponentially with increasing molecular chain orientation, prompting us to revise the classical Archard's law by including the effect of molecular chain orientation. These findings open the possibility of using neat PPS in highly demanding tribological applications.

Quantitative Investigation on Structural Evolution of Co-continuous Phase under Shear Flow

Components of co-continuous phase can form an interpenetrating network structure,which has great potential to synergistically improve the mechanical properties of the blends,and to impart the functional blends superior electrical conductivity and permeability.In this work,the effects of shear rates(50-5000 s^(-1))at different temperatures on the phase morphology,phase size and lamellar crystallites of biodegradable co-continuous polybutylene terephthalate(PBAT)/polybutylene succinate(PBS)blend are quantitatively investigated.The results show that the above features of the PBAT/PBS have a strong dependence on the shear flow and thermal field.The co-continuous phase of the blend is well maintained at 130℃.Interestingly,this phase structure transforms into a“sea-island”structure at 160℃,which gradually recovers to a co-continuous phase when the shear rate increases from 1000 s^(-1) to 5000 s^(-1).The phase size decreases with the increase of shear rate both at 130℃ and 160℃ due to the refinement and deformation of phase structures caused by strong shear stress.Unexpectedly,a unique phenomenon is observed that the shear-induced lamellar crystallites are oriented perpendicular to shear direction in the range of 500-5000 s^(-1) at 130℃,while the orientation of lamellar crystallites at 160℃ is along the shear direction within the whole range of shear rates.The degree of orientation for the PBAT/PBS blend crystals increases first and then decreases at both temperatures above.In addition,the range of shear rate has reached the level in the industrial processing.Therefore,this work has important guiding significance for the regulation of the co-continuous phase structure and the performance for the blend in the practical processing.

Vibration Assisted Extrusion of Polypropylene

A new homemade apparatus, i.e. vibration assisted extrusion equipment, is employed to extrude polypropylene. Vibration assisted extrusion is based on the application of a specific macroscopic shear vibration field. Reduction of apparent melt viscosity as a function of vibration frequency is measured at different screw speeds and die temperatures. The effect of the process is investigated by performing mechanical tests, differential scanning calorimetry studies, polarized light microscopy and wide-angle X-ray diffraction. It is found that, compared with conventional extrusion, vibration assisted extrusion could effectively improve the rheological properties of PP melt by incorporating an extra shear vibration field. Both the tensile strength and elongation at break increased under the shear vibration field. For vibration assisted extrusion samples, both the melting temperature and crystallinity increased, accompanied by remarkable grain refinement. Vibration assisted extrusion induced a significantly enhanced bimodal orientation with a high fraction of a^＊-oriented α-crystallites, while only a limited improvement in the flow direction orientation. A structural model, i.e. bimodal c-axis and a^＊-axis orientation of PP macromolecular chains, was adopted to explain the experimental results.