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2018, Volume 32 Issue 10 Publication date: 26 October 2018 Previous Issue Next Issue

Crosslinked Polyethylene for Rotational Molding and Its Application for Chemical Storage and Transportation

SUN Xiaojie, WANG Ke, LIANG Wenbin, ZHU Hexiang

2018, 32 (10): 1-12; DOI: 10.19491/j.issn.1001-9278.2018.10.001

Abstract ( 915 )

This paper overviewed the processing and performance characteristics of crosslinked polyethylene (PE)for rotational molding applications for chemical storage and transportation in domestic and abroad markets.A comparative introduction between the crosslinked PE and normal PE was proposed by focusing on the molecule structure, chemical resistance, high temperature resistance,mechanical properties and comprehensive service performance.Moreover, the application status of crosslinked PE in chemical storage and transportation containers was introduced, and the future development of the crosslinked PE used for transportation and storage containers was prospected.

A Brief Analysis of Safety Concerns for Plastic Food Packaging Materials in China

2018, 32 (10): 13-19; DOI: 10.19491/j.issn.1001-9278.2018.10.002

Abstract ( 656 )

This article summarized the development and classifications of plastic food packaging materials in China and analyzed the factors affecting food safety in detail, which included raw materials, processing aids, laws and rules, and the measurement methods and techniques of product quality.Some suggestions were also proposed for the improvement of food safety, including the clarification of government responsibilities, the enhancement of administration, the implementation of relevant standards and the enhancement of quality systems.Moreover, the enterprises should strengthen their selfmanagement, raise the awareness of selfdiscipline and enhance the investment in research and development of green materials.

Preparation and Properties of Glass Fiber-reinfreced PPS/PA66 Composites

2018, 32 (10): 20-26; DOI: 10.19491/j.issn.1001-9278.2018.10.003

Abstract ( 782 )

The PPS/PA66matrix composites with short glass fiber (SGF) and long glass fiber (LGF) were prepared in this work.Although the addition of PA66 led to a dramatic decrease in mechanical properties of PPS, the PPS/PA66/SGF composites presented slightly better mechanical properties than the PPS/SGF ones.On the other hand, the mechanical properties of PPS/PA66/LGF composites were much better than those of the PPS/SGF ones.It was proposed that the incorporation of glass fiber into the PPS/PA66 blend could make a stable rigid interlocked structure between two resins.Such an interlocked structure was confirmed by scanning electron microscopic observation and dynamic mechanical analysis.Compared to the PPS/SGF composites, the PPS/PA66/LGF ones presented a longer fiber length in the flow direction, thus leading to better mechanical properties.

Experimental Study on Performance of 3D-printing Polycaprolactone/Tourmaline Composites

2018, 32 (10): 27-31; DOI: 10.19491/j.issn.1001-9278.2018.10.004

Abstract ( 456 )

A series of polycaprolactone (PCL)based composites with different weight fractions of tourmaline were prepared by a melt blending method, and then their tensile, bending and impact test bars were fabricated by a 3D printer.The mechanical properties of the resulting test bars were evaluated.The experimental results indicated that the mechanical properties of composites were improved to some extent with the addition of modified tourmaline powders, and the composites also could release negative ions.The tensile and bending strength exhibited an increasing trend until the weight fraction of tourmaline reached 5 wt %, and then they tended to decrease.However, the elongation at break and impact strength of the composites decreased with an increase of tourmaline content.The dispersibility of tourmaline powders in the PCL matrix was greatly reduced at a weight fraction over 7 wt %.The composites also presented an improvement in release capability of negative ions due to the increase of tourmaline loading.

Effect of Wollastonite and Graphite on Friction and Wear Properties of Polytetrafluoroethylene

2018, 32 (10): 32-38; DOI: 10.19491/j.issn.1001-9278.2018.10.005

Abstract ( 526 )

Polytetrafluoroethylene(PTFE) composites with different contents of acicular wollastonite and flake graphite were prepared by a cold moldingsintering method, and their friction and wear properties were investigated by the analysis of worn surface and transfer film with scanning electron microscope (SEM).The results indicated that, although the wear rates of the composites decreased with an increase of wollastonite and graphite contents, the wollastonitefilled composites presented a lower wear rate at the same filler content.Compared to pure PTFE, the PTFE composites with graphite exhibited a smaller friction coefficient but the composites with wollastonite presented the higher value.Two different friction mechanisms could be deduced for the PTFE composites with different fillers according to the SEM observation on friction surfaces.The load dissipation was attributed to the accumulation of wollastonite at the sliding interface during the friction process, whereas the slipping and peeling effect of graphite in PTFE composites promoted the formation of transfer film.Moreover, the synergistic effect was achieved by a combination of 20 wt % wollastonite and 5 wt % graphite, which led to a further decrease in wear rate.The wear resistance of PTFE composites was improved by a factor of 200 compared to pure PTFE.

Study on Interfacial Properties of Hot-pressed PA6/Stainless Steel Samples

2018, 32 (10): 39-44; DOI: 10.19491/j.issn.1001-9278.2018.10.006

Abstract ( 544 )

The surface of 304 stainless steels was first disposed by polishing, etching and annealing to achieve micronano structures, and then the PA6/stainless steel samples were fabricated by a hotpressing molding method without using any adhesives.The mechanical characterization results indicated that the joint strength of the resulting samples was only 3.31 MPa after polishing.However, the joint strength of PA6/stainless steel samples reached 17.48 MPa after successively polishing, etching and annealing.There is a transition in failure mode observed from adhesive to cohesive.The surface morphologies of the samples were investigated by scanning electron microscopy and atomic force microscopy, and some micronano holes were observed on the surface of stainless steel after etching.It was deduced that the plastic melt could permeate into the micro and/or nano holes on the surface of stainless steel to generate an anchoring effect during the hotpressing molding process.Fouriertransmission infrared spectroscopic result indicated that PA6 was chemically bonded with the oxides on the annealed metal surface.Such anchoring and chemical bonding effects could improve the mechanical properties of PA6/stainless steel samples.

Study on Solubility and Diffusion Properties of CO₂ in PLA/PBAT Blends

2018, 32 (10): 45-49; DOI: 10.19491/j.issn.1001-9278.2018.10.007

Abstract ( 564 )

A theoretical model for calculating the solubility of CO2 in poly(lactic acid) (PLA) was established with a statistical mechanic density functional theory (DFT).The solubility and diffusion coefficients of CO2 in PLA and PLA/poly(butyleneadipatecoterephthalate) (PBAT) blends were determined by an exsitu gravimetric method.By comparing the experimental data with the theoretical calculation results, the DFT model was found to be able to quantitatively predict the solubility of CO2 in PLA at different temperatures and pressures.The addition of PBAT reduced the solubility of CO2 in PLA just with little effect on the diffusion coefficient.

Study on Toughening of Poly(lactic acid) with Vegetable Oil Polyol and L-lysine Diisocyanate Through In-situ Reactive Blending

2018, 32 (10): 50-57; DOI: 10.19491/j.issn.1001-9278.2018.10.008

Abstract ( 604 )

A novel type of fully biodegradable PLA compounds were prepared by using biobased and biodegradable soybean polyol (HM10100) and L-lysine diisocyanate (LDI) as reactivetoughening monomers via reactive blending.The effects of contents of two reactive monomers and the molar ratio of isocyanate groups (—NCO) and hydroxyl groups (—OH) on the mechanical properties and morphologies of the compounds were investigated.The results indicated that the PLA compounds achieved a maximum value in notched impact strength at the NCO/OH equivalent ratio of 1:0.8 (mol/mol) and the PLA/HM10100 & LDI weight ratio of 60/40.The notched impact strength was improved by a factor of 2.5 compared to that of pure PLA.Thermal analysis results indicated that the cold crystallization temperature and glass transition temperature of the compounds increased with an increase in the content of toughening monomers and the molar ratio of functional groups.

Preparation and Performance of CSH-reinforced PPC Composites for Bone Repair

2018, 32 (10): 58-64; DOI: 10.19491/j.issn.1001-9278.2018.10.009

Abstract ( 470 )

To enhance the performance of PPC and reduce the degradation speed of calcium sulphate hydrate (CSH), the PPC/CSH composites were prepared by a meltblending method, andtheir mechanical properties and degradability were investigated.The results indicated that the CSH prepared by a highpressure hydrothermal salt solution method was a semihydrate of calcium sulfate with a fibrous structure and large ratio of length to diameter, which made it suitable for the enhancement of polymer.The mechanical test results indicated that the introduction of CSH could improve the tensile strength and bending strength of PPC composites significantly, and however the elongation at break of the composites decreased gradually with an increase of CSH content.After added into PPC, the CSH still kept a good biological activity without any change in its crystalline structure.Morphological investigation indicated that the CSH was well dispersed in the matrix at a low content due to good compatibility, but an aggregation occurred at a high loading of CSH.The degradation rate of CSH was found to decrease significantly after blending with PPC, and its degradation rate could be well controlled. Moreover, the mechanical properties of PPC/CSH composites were improved.These results confirmed a good potential for the bonerepairing application of PPC/CSH composites.

Preparation of Conductive Porous Polyurethane Composite by Concentrated Emulsion Polymerization

2018, 32 (10): 65-70; DOI: 10.19491/j.issn.1001-9278.2018.10.010

Abstract ( 564 )

The porous polyurethane (PU) elastomer with a controllable pore size was prepared by a concentrated emulsiontemplating technique.Acidtreated multiwalled carbon nanotubes (MWCNTs) as a conductive additive were added into the elastomer to obtain a type of pressuresensitive conductive porous PU composites.The effects of contents of emulsifier and castor oil on the morphology of the composites were investigated.The results indicated that the average pore size decreased with an increase of emulsifier content, and the microsized pores were found to deform and deviate from a circular shape as the content of castor oil became higher.The addition of MWCNTs imparted the composites with a pressuresensitive conductive property.Furthermore, the electrical resistance of the composites decreased by two orders of magnitude with an increase of MWCNTs content.Meanwhile, the electrical resistance of the composites also decreased by two orders of magnitude with an increase in external pressure.

Foaming Behaviors of Poly (lactic acid) and Maleic Anhydride-grafted Linear Low-density Polyethylene Blends

2018, 32 (10): 71-78; DOI: 10.19491/j.issn.1001-9278.2018.10.011

Abstract ( 518 )

Poly (lactic acid) (PLA) was blended with maleic anhydridegrafted linear lowdensity polyethylene (PE-LLD-g-MAH) by a meltmixing method, and the crystallization behaviors, rheological properties and morphologies of the resulting blends at different content of PE-LLD-g-MAH were investigated by differential scanning calorimetry, rotational rheometer, scanning electron microscopy and polarizing optical microscopy.The results indicated that the crystallinity and melt elasticity of the blends were both improved with an increase of PE-LLD-g-MAH content, and a “seaisland” structure was clearly observed.Moreover, the cell sizes of PLA blending foams decreased but their cell densities increased with the addition of PE-LLD-g-MAH.

Fabrication of Super Hydrophobic Surfaces in the Way of Isothermal Hot Embossing in Solid-like State

2018, 32 (10): 79-86; DOI: 10.19491/j.issn.1001-9278.2018.10.012

Abstract ( 491 )

A superhydrophobic surface was fabricated on the plasticaluminum composite film by an isothermal hot embossing method in the solidlike state using a sifter covered with SiO2 microspheres as a mold through.The effects of impression pressure, sifter size and microsphere diameter on the microstructure and hydrophobicity of the resulting products were studied.The results indicated that the composite microstructure with a hydrophobic effect can be constructed on the surface of aluminumplastic composite films.The SiO2 microspheres could be well blended with PE matrix to form a composite system under a pressure, which led to a much stable connection between the matrix and SiO2 microspheres.The depth of the micrometer structure was improved with an increase of hotembossing pressure, and however the overloaded pressure might result in a cover of SiO2 microspheres with PE.The reasonable imprint pressure should be set as 8~12 MPa.The decrease of microsphere size could further result in an increase in water contact angle.The products achieved a superhydrophobic property when the water contact angle and rolling angle reached 150 ° and 1 °, respectively.

Rapid Optimum Design of Family Mould with Multiple Special-shaped Cavities for Unbalanced Filling

2018, 32 (10): 87-92; DOI: 10.19491/j.issn.1001-9278.2018.10.013

Abstract ( 642 )

Due to the imbalance of multiple specialshaped cavities in the family mould, there are some defects such as short shot and delaying effect easily caused during the injection molding process.This results in a poor quality of the formed products.Based on the melt flow analysis, the section radius and length of the runner were determined as two important factors affecting the volume flow and pressure distribution of the melt.Considering of the complex mold structures for indication lamp post, the maximum difference of filling pressures at the end of filling process among different subrunner was taken as an unbalance factor, and an integrated rapid optimum mechanism with a multivariate structure variety was constructed according to the uniform design method.The optimal runner scheme was obtained by combining with the global optimization of the genetic algorithm.The numerical simulation results indicated that the runner system with improved structure parameters has a better balance filling effect than that with the initial ones.

Analysis of Dynamic Characteristics of Internal Mixer Based on Fluid-solid Coupling

2018, 32 (10): 93-98; DOI: 10.19491/j.issn.1001-9278.2018.10.014

Abstract ( 434 )

The internal flow field and structure field of internal mixer were analyzed under three different conditions usinga calculation method based on oneway and twoway fluidsolid coupling.The equivalent stress in the maximum stress position and maximum displacement position of structure field were achieved, and the transient shear rate and fluctuation of maximum displacement were also obtained.The results indicated that the shear rate of flow field could be determined by the geometrical shape of rotor.The main frequency of shear rate fluctuation was one times of the rotor edge frequency.The results from the twoway coupling calculation were higher than those from the oneway coupling one.The stress of rotor edge and the distorted distribution were consistent with the two coupling calculation, and the main frequency of the fluctuation is mainly determined by the low frequency generated by rotor edge meshing.The rotor geometry was considered as a main influence factor of maximum stress wave.The stress wave had little effect on the rotation position frequency in the maximum stress point, but it had great effect on the maximum displacement position.

Warpage Optimization of Large-size Plate Plastic Parts Based on DOE, RSM and PSO

2018, 32 (10): 99-104; DOI: 10.19491/j.issn.1001-9278.2018.10.015

Abstract ( 395 )

Design of experiments (DOE) was first adopted to analyze the process parameters of a cabinet type air conditioning panel including melt temperature, mold temperature, pressure holding pressure and pressure holding time, which influenced the warpage deformation of the injectionmolded part significantly.Subsequently, the response surface methodology (RSM) was applied to construct the secondorder response surface model by taking four process parameters as experimental variables and the warpage of the panelas a goal.The process parameters with minimum warpage were optimized, which led to a high accuracy for the model as well as alow prediction error rate of 2.486 %.Finally, the optimal of process parameters were obtained by particle swarm optimization (PSO) for the twoorder response surface model.The verification results indicated that the optimization error of PSO was 4882 %.Compared to the RSM optimization, the actual value of warpage was reduced by 38367 % from 5217 mm to 3459 mm, which was reduced, suggesting that this optimization effect was much better.

Balanced Injection Optimization of Automotive Auxiliary Instrument Boxes Based on CAE

2018, 32 (10): 105-112; DOI: 10.19491/j.issn.1001-9278.2018.10.016

Abstract ( 468 )

In order to resolve the problems occurring in the balanced injection molding process for the plastic parts with a large volume and irregular shape, the scheme for threepouring injection was adjusted and the balanced injection was optimized through CAE auxiliary analysis.The warpage of the injectionmolded products was effectively controlled to about 15mm, which avoided the potential of the die scrap caused by the gating system set by experience.Based on the control of warping deformation, the optimum parameters for the injection molding process of products could be obtained for mold temperature at 245 ℃, for material temperature at 60 ℃, for two section holding pressures with 90 MPa/16 s and 70 MPa/9 s, and for cooling time with 60 s.An experimental injection molding process confirmed that the optimized process parameters met the requirement for massive production.The CAEassisted analysis can effectively predict the potential molding problems in injection molding and avoid the venture of improved production cost caused by simple experience.Therefore, the accuracy of designed mold and the production efficiency were improved significantly.

Effect of β-Nucleating Agent-loaded CaCO₃ Particles with Different Morphologies on Properties of PP

2018, 32 (10): 113-116; DOI: 10.19491/j.issn.1001-9278.2018.10.017

Abstract ( 466 )

Calcium carbonate (CaCO3) particles with cubic, spindle and spherelike morphologies were used as supporters to load heptane diacid as a βnucleating agent.The thermal behaviors and mechanical properties of PP blends with pure CaCO3 and heptane diacidloaded CaCO3 were investigated by differential scanning calorimetry and universal testing machine.The resultsindicated that the addition of CaCO3 improved the stiffness of PP blends, and the spindle CaCO3particles presented the least effect on mechanical properties.The incorporation of heptanediacidloaded CaCO3 not only improved the impact toughness of the blends but also generated a significant β-form nucleation effect on PP domain.The cubic CaCO3 particles could maintain a good stiffness for the blends, whereas the spindle CaCO3 particles exhibited the best toughening effect.The PP/sphere-like CaCO3 blends achieved a maximum improvement in impact strength up to 5.57 kJ/m2 compared to pure PP with the impact strength of 4.48 kJ/m2.On the other hand, the toughness of the blends was improved significantly with a decrease of the particle size of heptanediacid-loaded CaCO3.

Study on Biodegradation of Polycaprolactone Films with Lipase

2018, 32 (10): 117-122; DOI: 10.19491/j.issn.1001-9278.2018.10.018

Abstract ( 745 )

Poly(ε-caprolactone) (PCL) films were degraded by lipases and then were characterized by scanning electron microscopy (SEM), differential scanning calorimetry (DSC), thermogravimetric analysis (TGA), X-ray diffraction (XRD), nuclear magnetic resonance (NMR) and mass spectrometry (MS).The results indicated that the PCL films achieved a weight loss rate of 86.9 wt % when digested with 30 U/mL of lipase at 45 ℃ for 20 h.SEM observation showed that there were lots of pores formed on the film surface with an increase of degradation time, and the size of pores tended to increase with degradation time.DSC and XRD analyses indicated that the relative crystallinity of PCL gradually decreased with an increase of degradation time.The thermal stability of PCL films was found to decrease with an increase of degradation time according to the TGA results.NMR analysis demonstrated that there was no change for PCL films in chemical composition before and after enzymatic degradation.

Analysis and Solutions for Standard System of Non-metallic Pipeline Components

2018, 32 (10): 123-131; DOI: 10.19491/j.issn.1001-9278.2018.10.019

Abstract ( 351 )

This paper analyzed the current status of the standard system for nonmetallic pipe components in China and also compared it with that in other developed countries.The problems in the current standard system were also discussed, which included the imperfect system, outofdate rules, and deficiency in some key standards.Some specific solutions were proposed to establish and improve the standard system of China for nonmetallic pipe components, including the promotion of connection between the domestic and international standards, the enhancement of collaboration and coordination between the standard organizations, the improvement of development and update of standard items, etc.This paper provided some concrete solutions for the development of the standard system of nonmetal pipeline components in China.

Design of Injection Mould with the Second Sliding and Second Inclined Roof Mechanism Driven by Half Slide Block of Pot Body

2018, 32 (10): 132-137; DOI: 10.19491/j.issn.1001-9278.2018.10.020

Abstract ( 668 )

In this work, a twocavity single parting surface injection mould was designed by a combination of the characteristics of plastic parts.A type of complex structural demoulding mechanism with half slide blocks was designed with regard to the demoulding difficulty of plastic parts.In this complex mechanism, the entire circumference surface of the outer wall was demolded in a side core pulling mode by two half slide blocks in the main mechanism body.The left slide block of the half slide blocks was used to drive the core pulling and demoulding mechanisms of the inner core, and the right slide block was used to drive the lateral inclined top coring mechanism installed in the body of the right slide block to perform the upper side demodulation of the inner wall.This design for the complex demoulding mechanism with half slide blocks is fairly reasonable.Especially for the two submechanisms driven by the left and right sliders, the wellconceived design could effectively utilize the motion power of the half slider mechanism to perform a secondary drive, which led to a smart demodulation for the plastic parts with local complex features.The design of the mould release mechanism was simplified, thus leading to a decrease in difficulty of mould design.With a reasonable mould structure and reasonable and reliable mechanism layout, the mould designed in this work could be taken as a good reference for the design of similar moulds.

Design of Bi-color Injection Mould with Hot Runner, Complex Slides and Inclined Ejector

Qing-Dong LIU

2018, 32 (10): 138-142; DOI: 10.19491/j.issn.1001-9278.2018.10.021

Abstract ( 347 )

The forming process of a bicolor plastic part with characteristics of small size, high appearance and complex structures was analyzed, and then its injection mould was designed.Considering of an ejecting difficulty due to the plastic part obliquely placed in the mold, which resulted in nonperpendicular between the ejecting direction and stress surface, an inclined ejector mechanism was designed.Moreover, the corepulling mechanism with a Tshaped block, angle pin and ejector plate were designed with regard to the small size of the part and multiple corepulling places.For the reasons that the secondary injecting gate could not be set on the surface of the part and there were a lot of sliders around the part, a gating system with hot runners turning to the cold ones was also designed.The experimental results indicated that the mould structure was reasonable and reliable and met the requirement for production.