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2019, Volume 33 Issue 7 Publication date: 26 July 2019 Previous Issue Next Issue

Effect of Solid Phase Stretching on Aggregation Structure, Mechanical Performance and Thermal Properties of Polypropylene Sheet

2019, 33 (7): 1-5; DOI: 10.19491/j.issn.1001-9278.2019.07.001

Abstract ( 537 )

The effect of solid phase stretching on the microscopic crystalline structure and macroscopic physical properties of iPP sheet containing β-nucleating agent was investigated. The crystallization behavior of iPP sheet after solid phase stretching was studied by X-ray powder diffraction. The microstructure of iPP sheet was studied by scanning electron microscopy and polarized light microscopy. The physical properties of iPP sheet were evaluated by means of universal tensile testing machine, pendulum impact tester and softening point tester. The results indicated that the iPP sheet achieved the optimum mechanical properties at 130 ℃. The impact strength of iPP sheet was almost double of the value for the unstretched iPP one but its tensile strength showed an unchanged value.

Study on Olefin Block Copolymer by Multiple Fractionations

2019, 33 (7): 6-11; DOI: 10.19491/j.issn.1001-9278.2019.07.002

Abstract ( 477 )

To make a comprehensive analysis, preparative temperature rising elution fractionation (pTREF) and preparative molar mass fractionation (pMMF) are adopted to fractionate the olefin block copolymers (OBC) into fractions with narrower branching and molar mass distributions, respectively. The chain structure and composition of the bulk resins as well as the corresponding pTREF and pMMF fractions are further analyzed by means of gel permeation chromatography, crystallization elution fractionation, and differential scanning calorimetry. The results indicated that the multiple fractionations are a type of powerful approach to generate a library of OBC samples. Such a library can be composed by the fractions with similar molar masses but different branching structures or by the fractions with similar branching but different molar masses. Furthermore, the cross-fractionation was performed for these sample libraries by comprehensive analytical techniques to provide in-depth information on the molecular heterogeneity of OBC samples.

Effect of Calcium Stearate-modified Phosphogypsum on Mechanical Properties of PC/ABS Matrix Composites

2019, 33 (7): 12-18; DOI: 10.19491/j.issn.1001-9278.2019.07.003

Abstract ( 508 )

The PC/ABS matrix composites with calcium stearate-modified phosphogypsum (CSMP) were prepared by a melt extrusion method. The effect of contents of calcium stearate and CSMP on the mechanical properties of the composites was investigated, and the modification effect of phosphogypsum was evaluated by means of the contact angle of oil absorption value. Moreover, the microstructure and rheological properties of CSMP were studied by SEM and rheological test. The results indicated that the reaction between calcium stearate and phosphogypsum surface reduced the hydrophilicity of phosphogypsum. An optimum modification effect on mechanical properties was achieved for the composites when 0.5 wt % of calcium stearate was used to modify phosphogypsum. The optimum addition amount of CSMP was determined as 10 wt %. With such an optimum amount, the composites achieved the tensile strength of 45.29 MPa and bending strength 137.87 MPa, which increased by 9.10 % and 25.27 %, respectively, compared to pristine PC/ABS alloy. Moreover, the impact toughness also reached 11.50 kJ/m2, getting an increase by 26.37 %.

Influence Factors of Dimensional Stability on Glass Fiber-reinforced PA6

2019, 33 (7): 19-25; DOI: 10.19491/j.issn.1001-9278.2019.07.004

Abstract ( 655 )

Glass fiber-reinforced PA6 composites were prepared by melt-blending with a twin-screw extruder, and the effects of humidity, water absorption, nucleating agent and heat treatment on their dimensional stability were investigated. The results indicated that the hygroscopic expansion and internal stress release shrinkage affected the size of the composites, and the former was the dominant factor. The higher the ambient humidity, the longer was the time. As a result, the bigger was the size of the composites. Moreover, its size variation in the vertical flow direction was greater than that in the flow direction. The lower the environmental humidity, the longer was the time required to achieve the same water absorption rate, resulting in a larger size of the composites. With an increase of the content of nucleating agent, the size of the composites tended to decrease slightly. The size variation achieved a minimum value at a content of nucleating agent of 0.5 phr. However, the size changed little with further increasing the content of nucleating agent. The heat treatment promoted the internal stress release shrinkage of the composites, resulting in a decrease of size variation rate of the composites due to an opposite effect by hygroscopic expansion.

Preparation and Properties of Antibacterial Film Based on Nano-TiO₂-modified Low-density Polyethylene Composites

2019, 33 (7): 26-31; DOI: 10.19491/j.issn.1001-9278.2019.07.005

Abstract ( 435 )

A type of antibacterial films was prepared by a casting method using TiO2 nanoparticles (Nano-TiO2) as an antibacterial agents and low-density polyethylene (PE-LD) resin as a matrix, followed by hot compression with polyethylene terephthalate (PET) film as an outer layer. The mechanical, antibacterial and optical properties of the composite films were evaluated. The results indicated that, as the proportion of increases, the mechanical and antibacterial properties of the films were enhanced with increasing the loading of Nano-TiO2, whereas the optical properties tended to decrease. When 2.5 wt % of Nano-TiO2 was added, the tensile and haze strength of the films was higher than the pristine one. However, their light transmittance became smaller, but their gas resistance, water resistance and antibacterial effect became better. The composite films developed by this work can be used for the antimicrobial packaging of food.

Flame Retardancy and Reinforcing Mechanism of Boehemite-modified PET Composites

2019, 33 (7): 32-37; DOI: 10.19491/j.issn.1001-9278.2019.07.006

Abstract ( 578 )

The PET/boehmite (BM) composites were prepared using BM as a flame-retardant and reinforcement additive, and the effects of BM dosage on the mechanical, crystalline, thermal and flame-retardant properties of the composites were investigated. The experimental results indicated that the rigidity of the composites increased gradually with an increase of BM content, but the toughness tended to decrease gradually. The Tc and Tcc of the composites were found to increase and decrease gradually with an increase of BM content, respectively. However, the value of ΔT·(Tc-Tcc) shows a gradual increase. BM could act as a nucleation agent to promote the crystallization rate and the relative degree of crystallinity (Xc) of PET domain by heterogeneous nucleation. Nevertheless, the melting temperature of the composites presented a decrease with increasing the content of BM. BM could also generate good flame retardant effect on PET. The incorporation of BM resulted in an increase in char yield and a decrease in decomposition temperature for the composites. As a result, the thermal stability of the composites was improved during combustion. In summary, BM plays an important role in enhancement of mechanical, crystalline and flame-retardant properties for the PET/BM composites.

Comparative Investigation on Properties of Synergistic Flame-retardant TPU with IFR/SiO₂ and IFR/MgSiO₃

2019, 33 (7): 38-43; DOI: 10.19491/j.issn.1001-9278.2019.07.007

Abstract ( 500 )

The flame-retardant polyurethane (TPU) composites were prepared by using triazine charring-foaming agent and ammonium polyphosphate as intumescent flame retardants (IFR) and silica and magnesium silicate as synergistic agents. The flame retardant performance, mechanical properties, thermal decomposition behavior, surface morphologies and elemental compositions of char layers were investigated comparatively. The results indicated that the specimens with a thickness of 1.6 mm achieved a UL 94 V-2 classification when the total loading amount IFR of 30 wt % was added along with 5 wt % SiO2 corresponding to the IFR. However, a UL 94 V-0 classification was gained when 26 wt % of IFR and 5 wt % of MgSiO3 were incorporated. These results indicated that MgSiO3 could generate a good antidripping effect on the flame retardant system. Moreover, the incorporation of MgSiO3 had less influence on the tensile properties compared to SiO2. XPS analysis indicated that the introduction of MgSiO3 into the IFR/TPU composites improved the phosphorous content in the formed char layer. SEM observation demonstrated that MgSiO3 promoted the formation of a more continuous and compact char layer with higher strength during combustion. Consequently, the flame retardant performance of the composites was enhanced.

Study on Mechanical Properties and Thermal Stability of Halloysite-reinforced Polylactic Acid Composites

2019, 33 (7): 44-49; DOI: 10.19491/j.issn.1001-9278.2019.07.008

Abstract ( 461 )

Poly(lactic acid) (PLA)/halloysite (HNT) composites were prepared by a blending method, and the effect of HNT content on the mechanical properties, thermal properties and microstructure of the composites were investigated. The results indicated that there was a significant reinforcement effect of HNT on PLA, and the mechanical properties of PLA/HNT composites were greatly improved. The optimum mechanical properties can be obtained when 8 wt % of HNT was incorporated into PLA. However, the addition of HNT led to a decrease in elongation at break and impact strength of the composites. The relative crystallinity and melting temperature of the composites were improved in the presence of HNT. The thermal stability of the composites was also improved significantly. Moreover, the morphological observation indicated that the fracture surface of the composite became smoother, indicating a transformation from ductile fracture to the brittle one.

Optimization of Injection Molding Process Parameters for Automobile Gearlever Based on Orthogonal Experiment

2019, 33 (7): 50-56; DOI: 10.19491/j.issn.1001-9278.2019.07.009

Abstract ( 413 )

Aiming at various quality defects in the injection molding process of automobile gear lever, the warpage was selected as an optimization objective. The relationship between the experimental factors of mold temperature, melt temperature, injection molding time, packing pressure and holding time and the warpage deformation as experimental index were studied by means of the Taguchi experiment design method and Moldflow software. The order of influence degree for each factor on the warpage deformation of gear lever as well as the optimum combination of factors and levels were found. Then numerical simulation and injection molding were carried out to verify the validity of these results. As a result, the goal for improving the injection quality and shortening the production cycle of gear lever products was achieved.

Effects of FDM Process Parameters and Post-finishing on Forming Quality of PLA Cylindrical Parts

2019, 33 (7): 57-62; DOI: 10.19491/j.issn.1001-9278.2019.07.010

Abstract ( 437 )

To improve the dimensional accuracy and surface quality of fused deposition modeled parts, a cylindrical sample made from polylactic acid was used as an experimental object, and the effects of layer thickness, nozzle temperature, printing speed and filling rate on the dimensional accuracy of parts was studied by means of an orthogonal experimental design method. An optimal process parameter combination was developed on the based of a comprehensive balance method, in which a layer thickness of 0.1 mm, a nozzle temperature of 200 ℃, a printing speed of 60 mm/s and a infill density of 30 wt % were determined. Vapor smoothing was used to further improve the surface quality of the sample, and the effects of smoothing temperature and smoothing time on the surface roughness of the sample was investigated. The results showed that the roughness decreased with increasing smoothing temperature and smoothing time. After vapor smoothing at 50 ℃ for 7 min, the surface roughness was reduced from 9.227 μm to 3.435 μm. As a result, the surface quality of the sample was improved significantly.

Characterization, Analysis and Improvement of Internal Stress Cracks of PC

2019, 33 (7): 63-68; DOI: 10.19491/j.issn.1001-9278.2019.07.011

Abstract ( 1171 )

The difference of internal stress caused by different types of polycarbonate(PC) test specimens and its parts, different mold temperatures and different solvent resistance were characterized through a series of soaking experiments at different components and solvent concentrations. The effect of annealing process on the improvement of internal stress of the parts was verified, and the effects of stress and mechanical properties of the parts were quantitatively measured and analyzed. Furthermore, the solvent stress cracking mechanism of the parts were analyzed and discussed. The results indicated that CCl4 was not suitable to characterize the difference of stress and solvent resistance of PC due to its high corrosion, and however a mixture of toluene and n-propanol was suitable as a solvent for this characterization. The formation of PC/PBT alloys could effectively improve the resistance to solvent-induced crack of PC. The difference of mold temperature could give a more than 30 % influence on the numbers of stress crack of PC. The stress cracking problem of PC parts could be solved effectively by annealing at 110 ℃ for 2 h, and meanwhile, theirstrength was not reduced significantly.

Failure Analysis of LED Ball Packaging Colloid for a Lamp

2019, 33 (7): 69-73; DOI: 10.19491/j.issn.1001-9278.2019.07.012

Abstract ( 667 )

Aimed at the discoloration and dropping of the colloid for encapsulation of LED beads during the aging process of a lamp, the failure analysis was carried out in this work. The reasons of colloidal failure for LED bead packaging were analyzed by means of slice analysis, X-ray fluoroscopy, infrared spectroscopy, infrared thermal image analysis, and finite element analysis. The results indicated that there was serious discoloration occurred in the colloid close to the chip and the outer surface of lamp beads. The internal structure of the lamp beads is uniform in series, and the failure occurred in silicon resin with the normal sample. It was found that there was no influence of overall heat dissipation performance on the lamp beads. The results from finite element analysis and simulation validation indicated that the failure of packaging silicone resin resulted from the double effects of heat in the LED chip and heat accumulation in the cavity. It was suggested that the lamp support pillar should be opened or directly fabricated into a network structure, which may allow the static air between the reflector and support pillar to flow. Afterward, an optimization process was performed on the basis of the actual situation.

Study on Stabilizing Effect of Lanthanum P-methyl Benzoate as Heat Stabilizer on PVC

2019, 33 (7): 74-82; DOI: 10.19491/j.issn.1001-9278.2019.07.013

Abstract ( 487 )

Lanthanum p-methyl benzoate (LPB) was synthesized by using lanthanum chloride, p-Toluic acid and sodium hydroxide as raw materials, and the resultant product was characterized by means of elemental analysis and FTIR. The effect of LPB on the thermal stability and discoloration of polyvinyl chloride (PVC) were investigated by Congo red experiment and high-temperature hot aging tests. Moreover, a comparative study was carried out for LPB with other stabilizers such as zinc stearate, calcium stearete, lanthanum stearate and pentaerythrotol, and LPB was also mixed with other stabilizers to form a complex stabilizer. The results indicated that the thermal stabilizing effect on PVC is not good enough when LPB was used alone, which also resulted in poor long-term stability and anti-discoloration performance. When the mass ratio of LPB/calcium zinc composite/pentaerythrotol mixture was set to 2/1/2 and its total dosage was determined as 4 wt % of PVC, the stability time of PVC reached 48 min. The stable mechanism of LPB could be ascribed to the absorption of the HCl released by the decomposition of PVC. Such absorption could result in the production of LaCl3 and therefore reduced the catalytic effect of HCl on the degradation of PVC and inhibited the degradation of PVC accordingly.

Effect of RA-g-PHS Hyper-dispersant on Properties of PP/MCF Wood-plastic Composites

2019, 33 (7): 83-88; DOI: 10.19491/j.issn.1001-9278.2019.07.014

Abstract ( 311 )

The polypropylene (PP)/sisal cellulose microcrystalline (MCF) composites was prepared by use of rosin sea pine acid grafting poly(12-hydroxy stearic acid) (RA-g-PHS) as a hyper-dispersant, and the effect of hyper-dispersant content on the mechanical properties, melt flow rate and thermal properties of the composites were investigated. Moreover, the impact fracture surface of the composites was observed with scanning electron microscopy. The results indicated that the impact strength and melt flow rate of PP/MCF composites reached 16.8 kJ/m2 and 2.06 g/10 min, respectively, when 2 wt % of RA-g-PHS was incorporated. The composites also achieved optimum thermal properties.

Analysis on Gas Permeability of Barrier Plastic Films by Differential-pressure and Equal-pressure Methods

2019, 33 (7): 89-95; DOI: 10.19491/j.issn.1001-9278.2019.07.015

Abstract ( 510 )

The gas permeance of oxygen and carbon dioxide for four kinds of barrier plastic films were investigated by a differential-pressure method and/or an equal-pressure method. The effects of temperature, film type and thickness and relative humidity on the oxygen and carbon dioxide gas permeability of the films were analyzed, and the oxygen transmission rates obtained from the differential-pressure method and equal-pressure method were comparatively investigated. The results indicated that there was a remarkable influence of temperature on the oxygen and carbon dioxide gas permeance of PET film with thicknesses of 12 μm and 25 μm, PET/Al film with a thickness of 12 μm and PVDC film with a thickness of 25 μm. These three types of films showed a rise of gas permeance with an increasing of temperature. Moreover, the logarithmic values of gas permeance of the barrier plastic films are linearly relative to the reciprocal of thermodynamic temperature. The gas permeability of oxygen and carbon dioxide for the barrier plastic films are quite different in a descent order of the PET film with a thickness of 12 μm > the PET one with a thickness of 25 μm > the PVDC one with a thickness of 25 μm are smaller > the PET/Al one with a thickness of 12 μm. The ratios of gas transmission rate of carbon dioxide to oxygen for the barrier plastic films are all more than four times compared to the original ones. Therefore, the four types of barrier plastic films all possess an excellent barrier property and permselectivity.

Design of PTFE Piston Ring with C-type Cut and Its Applications in Transmission

2019, 33 (7): 96-101; DOI: 10.19491/j.issn.1001-9278.2019.07.016

Abstract ( 440 )

In order to seal the hydraulic oil in the transmission, a piston ring with C-type cut was designed. To provide a guide for dimension design, a dynamic stress analysis was simulated for the designed piston ring by the ABAQUS software. Meanwhile, a metal gauges with groove was designed to help the measurement of the size of piston ring. Finally, a practical test was carried out for the piston ring by customers. The test results indicated that the piston ring designed by this work could meet the requirements for transmission sealing. On the other hand, this test also confirmed that the analysis software used in this work could well serve for the design of sealing rings.

Design of Injection Mold with Core-pulling Mechanism of Bending Pin Driven by Front-pulling-plate for Bearing Front Cover

2019, 33 (7): 102-107; DOI: 10.19491/j.issn.1001-9278.2019.07.017

Abstract ( 246 )

Aimed at the demolding difficulties with three characteristics of plastic parts in automatic injection molding of shell plastic parts, a two-plate mould was designed. Banana gate was used to pour the mold. The die is divided into two parts, in which one is for the core pulling drive of the first core pulling mechanism of the front die and the other is for the opening of the cavity of the plastic part and the simultaneous completion of the side core pulling demolding of the reverse buckling of the outer wall of the plastic part. In order to realize the core-pulling function of the front-die core-pulling mechanism, a cylinder-driven top-plate mechanism was installed on the side of the fixed-die frame, which was used to drive the bending pin of the front-die inner-wall inverting front-die bending pin to drive the inner core-pulling slider in the cavity to realize the core-pulling-out and demolding of the inner-wall inverting of the plastic part. The slider of the outer-wall inverting of the plastic part is driven by the oblique guide pillar to implement the side. For core-pulling demolding, inclined hole is driven by cylinder core-pulling inclined core to demold. The layout of die structure is reasonable, and the mechanism design is ingenious. Such a design provides a good engineering reference for the mold design.

Current Status and Technical Requirements of Insulating Plastic Composite Pipes

2019, 33 (7): 108-116; DOI: 10.19491/j.issn.1001-9278.2019.07.018

Abstract ( 273 )

This paper instructed the application fields of the insulating plastic composite pipes and the associated social problems required for solution and also reviewed their performance advantages, structure and classification, standards and specifications. The technical requirements were summarized in accordance to the outer casing pipe, insulation layer, service pipe and whole pipe. Moreover, the core evaluation methods such as axial shear strength, environmental stress crack resistance, flexibility and insulation layer performance were analyzed in combination with the technical requirements.

Research Progress in Preparation of Microcellular PVC Foamed with Supercritical CO₂

2019, 33 (7): 117-129; DOI: 10.19491/j.issn.1001-9278.2019.07.019

Abstract ( 453 )

This paper overviewed the foaming technology for preparation of microcellular polyvinyl chloride (PVC) using supercritical carbon dioxide (CO2) as physical blowing agent and introduced the dissolution and diffusion behaviors of CO2 in PVC and the effect of high CO2 plasticization on PVC. The different PVC foaming processes including batch step temperature rising foaming process, batch rapid depressurization foaming process and continuous extrusion foaming process were discussed, and both advantages and disadvantages of each process are analyzed. The effects of foaming condition and PVC formula composition on the cell morphology and mechanical properties of the foamed samples were also analyzed in detail. The industrial applications of microcellular PVC foamed with supercritical CO2 were prospected.

Research Progress in Flame-retardancy of Unsaturated Polyester Resins

2019, 33 (7): 130-140; DOI: 10.19491/j.issn.1001-9278.2019.07.020

Abstract ( 379 )

The paper reviewed the development status of flame retardant technology for unsaturated polyester resins (UPR) from 1992 to 2018 and also introduced the additive-type and reactive-type flame retardants specially used for UPR. The additive-type flame retardant included inorganic nanoparticles, inorganic fibers and relevant modified compounds and in-situ polymerization flame retardants, and the reactive-type UPR flame retardants covered a variety of Si-, N-and P-containing monomer. Moreover, the flame retardant effects and associated mechanisms were also discussed.