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2018, Volume 32 Issue 06 Publication date: 26 June 2018 Previous Issue Next Issue

Development of Curing Process for Fiber-reinforced Resin Matrix Composites

2018, 32 (06): 1-9; DOI: 10.19491/j.issn.1001-9278.2018.06.001

Abstract ( 597 )

This paper reviewed the research and development trends in the most usually used four curing processes for fiber reinforced resin matrix composites, which include autoclave curing, electron beam curing, microwave curing and laser curing. Forthermore, the molding processes, curing mechanisms, advantages and disadvantages of these four curing processes were discussed, and their current technical problems and solutions were described. Finally, the most recent progress at home and abroad in this field was introduced, and the trend in development of curing technology for composite materials was discussed.

Research Progress in Multi-functionalization of Polymer/Graphene Composites

2018, 32 (06): 10-19; DOI: 10.19491/j.issn.1001-9278.2018.06.002

Abstract ( 623 )

Polymer/graphene nanocomposites can achieve some special performance like high strength, light weight, good heat resistance and electrical conduction. The paper reviewed the most recent industrialized situation of graphene at home and abroad as well as the status in the self-healing research of graphene. Moreover, state of the art for polymer/graphene nanocomposites were discussed, which included unique self-repairing performance, drug controlled release, metal anti-corrosion, electrical conduction, photocatalysis, microwave absorption and energy storage. The future application prospect of polymer/graphene nanocomposites was discussed especially in the fields of biomedical, electronic and new energy.

Research Progress in Crystallization of Polylactide Under Shear Effects

2018, 32 (06): 20-27; DOI: 10.19491/j.issn.1001-9278.2018.06.003

Abstract ( 544 )

This paper reviewed the studies on the effects of shear on crystallization kinetics, crystal morphology and crystal structure of polylactide (PLA). These studies indicated that the crystallization kinetics of PLA was improved remarkably by shearing effect, for example, the crystallization induce time was reduced and the nuclei growth rate was improved, thus leading to an increase in crystallinity of PLA. Moreover, the point-like, row-like and even shisi-like crystals could be formed for PLA under shear. This suggests that the crystalline morphology of PLA can be improved under shear. The shear effect can also result in a phase transition from α′-form crystals to the α-form one and, therefore, makes the crystal structure more perfect.

Effect of Low-temperature Cold Draw on Porosity of PVDF Microporous Membrane with Lamellar Crystalline Structure

2018, 32 (06): 28-34; DOI: 10.19491/j.issn.1001-9278.2018.06.004

Abstract ( 447 )

As a polymer with excellent mechanical strength, heat resistance ability and chemical stability, poly(vinylidene fluoride) (PVDF) was used to prepare microporous membrane for lithium battery through melt extrusion and post draw. A row-nucleated lamellar crystalline structure was achieved by adjusting the draw ratio during the process. The investigation results indicated that the casting film was highly orientated along the flowing direction. It is hard for cast film to gain a proper porous structure at room temperature stretching due to short relaxation time of PVDF, even if the cast film achieved the row-nucleated lamellar structure. Based on the time-temperature equivalence principle, the reduction of cold-drawing temperature can lead to the same effect by increasing relaxation time. More plastic deformation was generated in the amorphous region when the cast film was drawn at a low temperature below room temperature. By comparing the SEM images of the film drawn at different temperature, it was observed that the film cold-drawn at low temperatures exhibited much better porous structure and pore-size distribution. The formation mechanisms of microporous structure at low-temperature cold draw were also discussed.

Study on Grafting Rate of ACS Resin Synthesized by High Temperature Bulk Polymerization

2018, 32 (06): 35-39; DOI: 10.19491/j.issn.1001-9278.2018.06.005

Abstract ( 468 )

This paper conducted a study on the effects of polymerization condition, composition and chlorination degree of chlorinated polyethylene (CPE) rubber on the grafting rate of chlorinated polyethylene grafted with acrylonitrile and styrene (ACS resin) synthesized by high-temperature bulk polymerization. The results indicated that the grafting reaction mainly took place in the early stage at which the conversion was low than 50 %. The grafting rate of ACS resin was significantly affected by polymerization temperature and the content of initiator and chain transfer agent. The improvement of polymerization temperature or the content of initiator and chain transfer agent resulted in a significant decrease in grafting rate. However, the weight ratio of styrene/acrylonitrile, the content and chlorination degree of CPE showed fewer effects.

Effect of Types of Resin on Rheological Properties of PVC Plastisols

2018, 32 (06): 40-45; DOI: 10.19491/j.issn.1001-9278.2018.06.006

Abstract ( 572 )

The poly(vinyl chloride) (PVC) paste resins produced with different production methods were used to prepare a series of PVC plastisols, and the rheological properties of these plastisols were investigated by using rotational rheometer at a constant heating rate. The particulate morphology, molecular weight and molecular weight distribution of PVC paste resins were investigated by scanning electron microscope, laser particle analyzer and gel permeation chromatography correspondingly, and the relationship between the rheological properties of PVC plastisols and the characteristic parameters of paste resins were established. The results show that, with the increase of temperature, the rheological curves of PVC plastisols including energy-storage modulus, loss modulus, and complex viscosity tended to show a non-normal distribution. These curves demonstrated a four-stage variation in rheological parameters: (I) decrease, (II) slow rise, (III) rapid rise and maximization (IV) decrease. In the first three stages, the viscosity was mainly affected by the particulate morphology. However, with the gradual decrease of rheological parameters in the fourth stage, the viscosity was mainly affected by the molecular weight and its distribution of PVC paste resins.

Effect of MCC on Mechanical Performance and Thermal Stability of PLA/PPC Composites

2018, 32 (06): 46-52; DOI: 10.19491/j.issn.1001-9278.2018.06.007

Abstract ( 644 )

MCC/PLA/PPC composites were prepared by melt blending using PLA grafted with maleic anhydride (PLA-g-MAH) as a compatibilizer and MCC as a modifier. The effect of MCC on the mechanical properties, heat resistance and thermal stability of MCC/PLA/PPC composites were investigated by temperature-controlled stretching, dynamic thermal analysis, scanning electron microscopy and thermogravimetric analysis. The results shown that the tensile strength flexural strength was improved by 12.7 % and the glass translation temperature was increased by 9.8 ℃ when 40 wt% of MCC was added. On the other hand, the addition of 5 wt% PLA-g-MAH made the composites an increase in tensile strength by 53.7 %, in flexural strength by 43.1 % and in impact strength by 18 % due to an enhancement in interfacial adhesion. In this case, the breaking strength of the composites was also improved by 80 % at 60 ℃. Moreover, the thermal degradation temperature and maximum weight-loss temperature of the composites were improved by 25.31 and 61.83 ℃ compared to PLA/PPC composite, respectively.

Preparation and Properties of PE-LD/Paraffin Based Composite Phase Change Energy Storage Materials

2018, 32 (06): 53-58; DOI: 10.19491/j.issn.1001-9278.2018.06.008

Abstract ( 650 )

A series of composite phase change materials (PCMs) were prepared by using solid paraffin and lowdensity polyethylene (PE-LD) as raw materials, diatomite/expanded graphite modified with vinyl triethoxysilane as fillers and dicumyl peroxide (DCP) as a crosslinking agent. The effect of contents of paraffin and modified diatomite/expanded graphite on thermal stability and thermal conductivity of the composite PCMs were studied, and the effects of DCP content on their microstructure and mechanical properties were also discussed. The results indicated that the composite PCMs exhibited a good thermal stability at the paraffin loading of 60 wt%, and they also presented proper phase-change latent heat and phase-change temperatures. The addition of expanded graphite and diatomite improved the thermal stability of composite PCM, and an optimum thermal stability was achieved at a content of 4.6 wt%. The thermal enhancement effect was better from expanded graphite than from diatomite.; The addition of 4.6 wt% expanded graphite made the composite PCMs an improvement in thermal conductivity by 384.38 %. The mechanical properties of composite PCMs were enhanced with the addition of DCP, and the composite PCMs achieved optimum overall properties when 3 wt% DCP was added.

Effect of Composition on Ductility of PP/PE-LD Water-foamed Injection-molded Parts

2018, 32 (06): 59-64; DOI: 10.19491/j.issn.1001-9278.2018.06.009

Abstract ( 617 )

Compounding or blending is normally considered a good method to produce new polymeric materials for special uses. However, the ductility of polypropylene (PP)/low-density polyethylene (PE-LD) blends is relatively poor. PP/PE-LD microporous samples were prepared via conventional injection molding using water as a blowing agent, and their mechanical properties and microstructure were investigated. The results suggest that the formation of microporous structure enhanced the ductility of PP/PE-LD blends, and their mechanical properties and microstructure were influenced by the compositions of PP/PE-LD blends. A fine microporous structure was observed in the PP-content range of 90 %~50 %, which was attributed to the poor compatibility between the PP and PE-LD phases. This makes the ductility improved much easilier.

Crystalline Structure and Morphology of Biaxial Oriented Polypropylene Film Under Coexistence of Silica Nanoparticles

2018, 32 (06): 65-71; DOI: 10.19491/j.issn.1001-9278.2018.06.010

Abstract ( 427 )

The PP/EVA/nano-SiO2 composites were prepared by melt blending, in which the nano-SiO2 was surface-treated with EVA, and then, a surface-modified BOPP film was prepared by using the resulting composites. The surface morphology and cross-section of the film were observed by scanning electron microscopy, and their degree of crystallinity, molecular orientation and grain size were detected by X-ray diffraction measurement. Furthermore, the presence of microholes in the film was confirmed by positron annihilation spectroscopy, and the relationship between the crystalline structure and morphology and the solvent residue was investigated. The results indicated that the modified BOPP film not only had a higher degree of crystallinity and smaller grain size than the unmodified one, but also had a dense surface structure and reticular fiber bundle internal structure. These characteristic structures make the diffusion coefficient and solubility of ethyl acetate small in the film, thus improving the mechanical properties significantly.

Preparation and Properties of Poly(lactic acid)/Polyurethane Blends via In-situ Reaction

2018, 32 (06): 72-78; DOI: 10.19491/j.issn.1001-9278.2018.06.011

Abstract ( 580 )

A series of poly(lactic acid) (PLA)/polyurethane (PU) blends were prepared by in-situ reaction of PLA with poly(tetramethylene ether glycol) (PTMG) and carbodiimide-modified MDI (L-MDI). The reaction principle, mechanical properties, fracture morphology, dynamic rheological properties and crystalline properties of the resulting blends were investigated. The results indicated that micro-crosslinked polyurethane was formed during the in-situ reaction process along with the chain extension and branching of PLA. The mechanical results demonstrated that the toughness of PLA/PU blends was significantly enhanced, and their elongation at break, tensile toughness and notch impact strength were improved by 230 %, 134.13 MJ/m3 and 34.19 kJ/m2, respectively, compared to pure PLA, when 30 wt% of PU was incorporated. The toughening mechanism may be due to the crazes and shear zones induced by PU rubbery phase in the matrix. The rheological results indicated that the melts of pure PLA and its blends with PLA were pseudoplastic fluid, and however, the blends had a higher storage modulus and complex viscosity. The crystallization test suggested that the PLA/PU blends had a higher crystallization rate and more perfect level of crystallization in comparison with pure PLA.

Study on Properties of Epoxy Resin Impact-modified with ATBN

2018, 32 (06): 79-83; DOI: 10.19491/j.issn.1001-9278.2018.06.012

Abstract ( 530 )

The epoxy resin/polyether amine thermosetting system was modified with amineterminated liquid ATBN as a impact modified, and their gel time, morphology and mechanical properties were investigated. The results indicated that this thermosetting system obtained a significant toughening effect when 15 phr of ATBN was added. Compared to pristine epoxy resin, the impact modified thermosetting system achieved an improvement in impacted strength by 65 %, in bending strength by 14 % and in tensile shear strength by 73 %.

Study on Numerical Simulation for Dispersion Process of PP Melt Droplet on Cross Section of Mixer

2018, 32 (06): 84-91; DOI: 10.19491/j.issn.1001-9278.2018.06.013

Abstract ( 394 )

Through the secondary development of Fluent, the flow of polymer viscoelastic fluid was simulated by loading a user-defined function into the viscoelastic fluid momentum equation and deformation tensor transport equation in Fluent. A VOF interfacetracking method was used to analyze the deformation, breakup and coalescence process of a single droplet in the polymer melt under the cross-sectional flow field of a mixer. The dispersion process and microstructural formation mechanism of the single droplet in the complex flow field were discussed. The relevant results are instructive to explore the evolution process and mechanism of morphology development in the process of blending modification. The results indicated that the PP droplet underwent deformation, breakup and coalescence during the mixing process. The inhomogeneous deformation behavior of PP droplet happened in the C-shape zone, which resulted in the occurrence of stretching, squeezing and crossover behaviors under the chaotic flow field of interaction window. The fragmentation behavior of PP droplet included capillary instability, pinch pinching and breakup during relaxation.

Effect of 3D Printing Parameters on Interlayer Adhesive Properties of Printed Parts

2018, 32 (06): 92-97; DOI: 10.19491/j.issn.1001-9278.2018.06.014

Abstract ( 671 )

A series of standard tensile and impact test bars were prepared via fused deposition modeling on a desktop 3D printer, and the effects of the printing parameters (including nozzle temperature, print height, et al), annealing or not, and the type of printing materials on the interlayer adhesion of printed part were investigated. The ABS and PLA samples presented an enhancement in tensile strength and elongation with increasing nozzle temperature, and however they were reduced with increasing layer height. SEM observation demonstrated that, with an increase of print height, the interfacial porosity of ABS and PLA samples was improved but their bonding area in wire decreased. The residual stress of ABS sample was removed by annealing, leading to an improvement in tensile strength and toughness. The crimp-cracking phenomenon became serious for PLA sample, followed by a decrease in tensile strength and toughness.

An Outlook on Design and Maintenance of Aircraft-used Composite Materials

2018, 32 (06): 98-103; DOI: 10.19491/j.issn.1001-9278.2018.06.015

Abstract ( 459 )

This paper proposed the vital problems in structure design, manufacturing and maintenance of aircraft-used composite materials according to the summarized cases of aircraft maintenance home and aboard. These problems covered the design of sandwich structure under the impact load, handle of the contact points between sandwich panel and air duct, treatment of front edges of composite parts, design of fastener hole, applications of blind fasteners and aramid components and many more. It was concluded that adhesives were recommended to use in the thin composite parts, and however co-curing process should be adopted to improve the rigidity of composite parts. Furthermore, the relative maintenance problems should be paid attention to for the co-cured parts.

Study on Laser Marking Foaming Model for Black PBT Materials

2018, 32 (06): 104-111; DOI: 10.19491/j.issn.1001-9278.2018.06.016

Abstract ( 526 )

In this paper, the foaming mechanism of the laser marking of black PBT material was studied, and the corresponding mathematical model was established. The theoretical analysis indicated that the main factors affecting the laser marking effect of black PBT material included the coverage of bubbles, the absorption coefficient of bubble wall, and the height and diameter of the bubble hole. The model analysis suggested that the test light reflected, refracted and transmitted on the surface of the bubble when irradiated on the laser marking area. The coverage of bubbles was considered as the main factor affecting the lasermarking effect. It is found that the L value of the laser marking increased from 42.6 to 72.8 by adjusting the coverage of bubbles, and meanwhile the value of ΔE was improved from 15.1 to 42.8.

Stress Relaxation Model and Safety Assessment of Polyethylene Pipe Welded Joints

2018, 32 (06): 112-118; DOI: 10.19491/j.issn.1001-9278.2018.06.017

Abstract ( 542 )

This paper reported a study on the stress relaxation behavior of polyethylene (PE) pipe-welded joint under the mechanical load condition by an experimental method. A crack defect model was established for PE pipe-welded joint by a combination of the finite element analysis software Abaqus, and the stress intensity factor for the PE pipe with crack defects was calculated by importing the Prony series of PE pipe-welded joint and pipe-grade PE resin. This article provides a proper fracture criterion for PE materials to determine their critical stress intensity factor and stress intensity factor so that a safety assessment could be well conducted for defective PE pipes.

Preparation and Properties of Poly(butyleneadipate-co-terephthalate)/Bamboo Powder Composites with Polyvinyl Butyral as Interfacial Modifier

2018, 32 (06): 119-123; DOI: 10.19491/j.issn.1001-9278.2018.06.018

Abstract ( 429 )

This paper reported an investigation on the effect of polyvinyl butyral (PVB) as a nonreactive interfacial modifier on the interfacial adhesion and mechanical properties of wood-plastic composites based on poly (butyleneadipate-co-terephthalate) (PBAT) and bamboo powders. It is understandable that the hydroxyl and acetal groups of PVB can interact with the polar groups of bamboo powders and polyester matrix, respectively, makes PVB a capability of interfacial modification. The results indicated that the interfacial adhesion between the bamboo powders and PBAT matrix was improved significantly. There is no significant influence on the mechanical properties of composites from the addition mode of PVB. The tensile strength of the composite was improved from 5.16 MPa to 6.02 MPa at a bamboo-powder content of 30 wt% when 1 wt% PVB in bamboo powders was incorporated.

Preparation and Properties of Carbon Fiber-based Composites Co-modified with Graphene and Carbon Nanotubes

2018, 32 (06): 124-130; DOI: 10.19491/j.issn.1001-9278.2018.06.019

Abstract ( 750 )

A type of polyacrylonitrilebased carbon fiber (MPG) was co-modified with KH570-surface-treated graphene and acidified multi-walled carbon nanotubes (MWCNTs), and then the MPG/MWCNTs/graphene composites (MPG-P) was prepared by a wet-processing method. The resulting MPG was characterized by Fourier-transform infrared spectroscopy and scanning electron microscopy. Furthermore, the electrical conduction, mechanical properties, pore size distribution and porosity of MPG-P were investigated by four-probe tester, universal testing machine and porous material analyzer. The results indicated that the composites achieved the optimum tensile strength of 37.21 MPa when 0.2 wt% of MWCNTs and graphene was incorporated, and their electrical resistivity and porosity reached 13.17 mΩ·cm and 63.7 %, respectively. The tensile strength reached an optimum value of 44.95 MPa at an MWCNTs/graphene mass ratio of 1∶2, which increased by 48.94 % compared to pristine carbon fiberbased composite. At this mass ratio, the resistivity and porosity also reached 13.52 mΩ·cm and 62.57 %, respectively.

Effect of Content of Peanut Hull Powders on Properties of PLA/Peanut Hull Powder Composites

2018, 32 (06): 131-135; DOI: 10.19491/j.issn.1001-9278.2018.06.020

Abstract ( 386 )

PLA/peanut hull powers composites were prepared by a compression molding method, and the effect of content of peanut hull powders on the mechanical properties, water absorption, wear performance and crystallinity of the composites were investigated. The results indicated that the Rockwell hardness and impact strength of the composites were found to decrease at first and then increased with an increase of content of peanut hull powders, and however the tensile strength and flexural strength tended to increase gradually up to a maximum value at the peanut hull content of 50 wt%. Moreover, the water absorption tended increase gradually but the wear performance decreased gradually with increasing the content of peanut hull powders. The optimum content of peanut hull powders was determined as 50 wt% on the basis of the experimental results, at which the composites exhibited good mechanical properties and low water absorption.

Design of Metal-powder Injection Mold Based on Hot Runner and Two-step Demolding Technology

2018, 32 (06): 136-140; DOI: 10.19491/j.issn.1001-9278.2018.06.021

Abstract ( 350 )

Based on the structural characteristics of parts and the metal powders plus polyamide molding characteristics, a metal-powder injection mold was designed, and its molding parts, side corepulling mechanism, gating system, die release mechanism, fixed distance classification mechanism, orientation system and temperature control system were mainly studied to determine a reasonable mold structure. Through designing a combined structure of hot runner casting, two ejection mechanisms and straight pipe plus buffle-type well cooling water channel, the molded part achieved dimensional tolerance in the range of 0.4 % of the basic dimension. Moreover, the angle tolerance and surface roughness reached 0.5 ° and 0.8, respectively.

Design of Injection Mold for Rearview Mirror Bracket of Automobile with Differential Combined Core-pulling

2018, 32 (06): 141-146; DOI: 10.19491/j.issn.1001-9278.2018.06.022

Abstract ( 341 )

Based on the structural characteristics of rearview mirror bracket of automobile, an injection mold with double-parting surfaces was designed by use of UG NX. A reasonable submarine gate location was selected with the help of the computer-assisted engineering analysis and the practical design experience of die and mold. Aiming to difficult processing problems, the insert inlaid way was used for the shaped part. Aiming at the difficult problem of demolding, the different types of side core-pulling mechanism were designed, especially for the two-way angled core-pulling in the same position. An innovative differential combined corepulling demolding mechanism was designed. Such a structural design was confirmed to be reasonable and stable.