Influence of molecular weight on rheological,thermal, and mechanical properties of PEEK

This study focuses on the influence of molecular weight on the rheological, thermal, and mechanical behavior of poly(ether‐ether‐ketone) (PEEK), a semicrystalline high‐performance polymer. The results show that the molecular weight of PEEK has significant influence on its rheological, thermal, and mechanical behavior. It was found that PEEK has the unique characteristic of two shear‐thinning regions. The shear viscosity and the stress relaxation time of PEEK increase significantly as molecular weight increases. In general, the Cox‐Merz rule is valid for all grades of PEEK. As molecular weight increases, the melting temperature of PEEK decreases slightly, but its isothermal and nonisothermal crystallization temperatures drop dramatically. As molecular weight increases, the crystallinity, the crystallization rate, and the magnitude of crystallization activation energy decrease. The crystallization kinetics study indicates that PEEK tends to form spherical crystalline structures, regardless of its molecular weight. As molecular weight increases, the tensile strength at yield, the tensile modulus, and the flexural modulus of PEEK decrease slightly, whereas the tensile strength at break, the tensile strain at break, the modulus of toughness, and the impact strength of PEEK increase significantly. POLYM. ENG. SCI., 2011. © 2010 Society of Plastics Engineers     

Influence of compatibilizers on mechanical properties,crystallization, and morphology of polypropylene/scrap rubber dust blends

Polypropylene blends containing a dispersed phase of scrap rubber dusts obtained from sport shoes manufacture; midsole (M, vulcanized EVA foam) and outsole (O, vulcanized rubber blend of NR, SBR, and BR) were studied. The influence of various compatibilizers on the mechanical properties of these blends were investigated. Significant development of impact strength was attained by using 6 and 10 phr of styrene–ethylene–butylene–styrene (SEBS) and maleic anhydride‐grafted styrene–ethylene–butylene–styrene (SEBS‐g‐MA) as compatibilizers for both compounds filled with midsole and outsole dusts. The tensile strength of each compound was slightly decreased when the compatibilizer loading increased, whereas the elongation at break was significantly increased. The enhancements of the impact strength and the elongation at break are believed to arise from reduction of interfacial tension between two phases of the rubber and the PP, which results in some reduction of the particle size of the fillers. Scanning electron microscopy (SEM) confirmed the evidence of the reduction of scrap rubber dust into small rubber particle sizes in the compound, and also showed the occurrence of some fibrils. Optical microscopy (crossed polars) observations suggested that the addition of the rubber dust resulted in a less regular spherulite texture and less sharp spherulite boundaries. © 2002 Wiley Periodicals, Inc. J Appl Polym Sci 86: 148–159, 2002     

Multiwalled carbon nanotubes‐reinforced isotactic polypropylene nanocomposites: Enhancement of crystallization and mechanical,thermal, and electrical properties

Multiwalled carbon nanotubes (MWCNTs)‐reinforced isotactic polypropylene (iPP) nanocomposites with low‐content of MWCNTs were fabricated using the melt‐cast techniques. The reinforced plastics were characterized by X‐ray diffraction (XRD) measurements, scanning electron microscopy (SEM), Fourier transform infrared (FTIR) spectroscopy, mechanical test, differential thermal analyses (DTA), and electrical tests. XRD studies exhibit the α‐crystal in the injection‐molded neat iPP with lamellar stacks having a long period of 150Å. Both the intensity of lamellar reflection and the thickness of long period increase with increasing the MWCNTs contents, indicating an enhancement of iPP crystallization by MWCNTs addition. This increase of lamellar thickness is analyzed to be consistent with that evaluated by DTA. SEM micrographs display larger MWCNTs aggregates with increasing amount of reinforcements and show a good adhesion between nanoparticles and iPP matrix. FTIR spectra reveal distinct chemical textures for the samples and confirm the existence of α‐crystal. Mechanical strengths, electrical conductivity, and dielectric constants are found to increase with increasing MWCNTs content, representing an improved performance of the nanocomposites. POLYM. COMPOS., 2012. © 2012 Society of Plastics Engineers     

Influence of thermal treatments,molecular weight,and molecular weight distribution on the crystallization of β‐isotactic polypropylene

Six samples of isotactic polypropylene were examined to study the influence of the thermal treatments and the molecular weights and their distribution on the β‐crystallization of the polymer. The highest amount of the β‐phase was obtained by isothermal crystallization and in correspondence of high average molecular weights and wide molecular weight distributions. Small‐angle X‐ray scattering pointed out that a partial β‐crystallization seems not to influence the lamellar morphology parameters. Differential scanning calorimetry measurements, at different heating rates, allowed us to confirm that the multiple melting endotherms behavior of the β‐phase is to be correlated to a melting–recrystallization–melting mechanism. © 2003 Wiley Periodicals, Inc. J Appl Polym Sci 91: 1008–1012, 2004     

成核剂对聚丙烯力学性能与结晶行为的影响

研究了两种类型的成核剂对国产共聚聚丙烯的结晶形态以及拉伸强度、冲击强度的影响。结果表明:加入TMB-5型成核剂,聚丙烯的冲击强度有一定程度改善,w(TMB-5)为0.1%时,改性聚丙烯的缺口冲击强度达到最大;TMX-2型成核剂可改善聚丙烯的拉伸性能,但抗冲击性能降低较大;TMB-5型成核剂可显著地改变聚丙烯的结晶行为,诱导聚丙烯在结晶过程中主要形成β晶;TMX-2型成核剂可诱导聚丙烯在结晶过程中主要生成α晶,与纯PP相比,α晶的形成能力增强。     

Bamboo fiber reinforced polypropylene composites and their mechanical,thermal, and morphological properties

Short bamboo fiber reinforced polypropylene composites were prepared by incorporation of various loadings of chemically modified bamboo fibers. Maleic anhydride grafted polypropylene (MA‐g‐PP) was used as compatibilizer to improve fiber–matrix adhesion. The effects of bamboo fiber loading and modification of the resin on the physical, mechanical, thermal, and morphological properties of the bamboo reinforced modified PP composites were studied. Scanning electron microscopy studies of the composites were carried out on the interface and fractured surfaces. Thermogravimetric analysis and IR spectroscopy were also carried out. At 50% volume fraction of the extracted bamboo fiber in the composites, considerable increase in mechanical properties like impact, flexural, tensile, and thermal behavior like heat deflection temperature were observed. © 2010 Wiley Periodicals, Inc. J Appl Polym Sci, 2011     

Isothermal crystallization of isotactic polypropylene blended with low molecular weight atactic polypropylene. Part I. Thermal properties and morphology development

The thermal properties and morphology development of isotactic polypropylene (iPP) homopolymer and blended with low molecules weigh atactic polypropylene (aPP) at different isothermal crystallization temperature were studied with differential scanning calorimeter and wide-angle X-ray scattering. The results of DSC show that aPP is local miscible with iPP in the amorphous region and presented a phase transition temperature at T_c=120 °C. However, below this transition temperature, imperfect α-form crystal were obtained and leading to two endotherms. While, above this transition temperature, more perfect α- and γ-form crystals were formed which only a single endotherm was observed. In addition, the results of WAXD indicate that the contents of the γ-form of iPP remarkably depend both on the aPP content and isothermal crystallization temperature. Pure iPP crystallized was characterized by the appearance of α- and γ-forms coexisting. Moreover, the highest intensity of second peak, i.e. the (0 0 8) of γ-form coexisting with (0 4 0) of α-form, and crystallinity were obtained for blended with 20% of aPP, the γ-form content almost disappeared for iPP/aPP blended with 50% aPP content. Therefore, detailed analysis of the WAXD patterns indicates that at small amount aPP lead to increasing the crystallinity of iPP blend, at larger amount aPP, while decreases crystallinity of iPP blends with increasing aPP content. On the other hand, the normalized crystallinity of iPP molecules increases with increasing aPP content. These results describe that the diluent aPP molecular promotes growth rate of iPP because the diluent aPP molecular increases the mobility of iPP and reduces the entanglement between iPP molecules during crystallization.     

Ultrahigh molecular weight polyethylene/polypropylene/organo‐montmorillonite nanocomposites: Phase morphology,rheological, and mechanical properties

Phase morphology, rheological, and mechanical properties of ultrahigh molecular weight polyethylene (UHMWPE)/PP/organo‐montmorillonite nanocomposites were investigated in this work. The results of TEM and XRD indicated that the organo‐montmorillonite PMM prepared with the complex intercalator [2‐methacryloyloxyethyldodecyldimethylammonium bromide/poly(ethylene glycol)] were exfoliated and dispersed into UHMWPE matrix, and the synergistic effect of the complex intercalator on the exfoliation and intercalation for montmorillonite occurred. Besides, the presence of PMM in UHMWPE matrix was found able to lead to a significant reduction of melt viscosity and enhancement in tensile strength and elongation at break of UHMWPE, except that izod‐notched impact strength was without much obvious change. The dispersed PMM particles exhibited a comparatively large two‐dimensional aspect ratio (L_clay/d_clay = 35.5), which played an important role in determining the enhancement of mechanical properties of UHMWPE nanocomposites. © 2007 Wiley Periodicals, Inc. J Appl Polym Sci, 2007     

Effect of molecular weight distribution on the rheological and mechanical properties of polypropylene

The effect of molecular weight distribution on the Theological and mechanical properties of a series of polypropylenes is evaluated. The polypropylenes tested were produced by controlled chemical degradation in a single-screw plasticating extruder. Measured properties include shear, extensional and intrinsic viscosity, melt flow index, extrudate swell, melting and crystallization temperatures, impact strength, flexural modulus, and tensile stress.     

Mechanical properties,thermal, and crystallization behavior of polypropylene composites reinforced by starch and wasted cotton cloth

In this study, wasted cotton cloth was bonded with soluble starches as an adhesive, then dried, cut into fiber fragments and filled into polypropylene (PP) to achieve resource efficiency. The mechanical, thermal, and crystallization properties of the composites were characterized. The results indicated that with the addition of wasted cotton cloth treated without or with silane coupling agent (RC or TRC), PP composites' tensile strength, impact strength, and flexural strength have been improved. The heat distortion temperatures increased slowly, indicating that wasted cotton cloth filled into PP can be turned back into useful items without degradation of PP composites exhibited. Thus, it is a good avenue for the utilization of an otherwise wasted cotton cloth resource. The crystallization activation energy, nucleation constant, and folding surface free energy of PP were markedly reduced in PP/RC composites and its compatibilized composites. The value of F(T) gradually increased with the increasing relative degree of crystallinity. The addition of wasted cotton cloth could significantly reduce the spherulitic size of PP. © 2011 Wiley Periodicals, Inc. J Appl Polym Sci, 2011     

Influence of organophilic montmorillonite and polypropylene on the rheological behaviors and mechanical properties of ultrahigh molecular weight polyethylene

The effects of organophilic montmorillonite (OM)/poly(ethylene glycol) (PEG) hybrids and polypropylene (PP) on the phase morphology, rheological behaviors, and mechanical properties of ultrahigh molecular weight polyethylene (UHMWPE) were investigated. The presence of the OM/PEG hybrids and PP in UHMWPE was found that it was able to lead to a significant reduction of melt viscosity and enhancement in tensile strength, and elongation at break of UHMWPE. A quantitative analysis indicated a larger affinity of the OM to the PEG than to PP or UHMWPE in the composites, suggesting that OM was intercalated by PEG. This was proposed to be responsible for the reduction of viscosity. Polarizing optical microscopy analysis, on the other hand, indicated that the dispersed OM, which acted as a nucleating agent, lowered the spherulite dimension and increased the spherulite number, resulting in high tensile strength and elongation at break. © 2007 Wiley Periodicals, Inc. J Appl Polym Sci, 2007     

Influence of the molecular weight on the thermal and mechanical properties of ethylene/norbornene copolymers

A series of ethylene‐norbornene copolymers were synthesized using Me₂Si(Me₄Cp)(NtBu)TiCl₂ as the metallocene catalyst and methylaluminoxane (MAO) as the cocatalyst, with the same molecular characteristics except the molecular weight, to evaluate its influence on the determination of the glass transition temperature (T_g). The polymers were characterized using wide‐angle X‐ray scattering, differential scanning calorimetry, microhardness measurements, and dynamic mechanical thermal analysis. The value of the T_g, for the same norbornene content and determined from the last three mentioned methods, increases significantly up to a limit of M_n about 6–10 × 10⁴ (g/mol). Above this value, T_g remains practically constant. © 2003 Wiley Periodicals, Inc. J Appl Polym Sci 89: 3358–3363, 2003     

Influence of process parameters on mechanical properties of physically foamed,fiber reinforced polypropylene parts

Due to the high complexity of the foaming technology, the relationship between processing and final properties of parts produced is not completely understood. Investigating the causality chain Processing–Morphology–Properties is of great importance, especially for the automotive industry, in order to be able to tailor the mechanical properties of foamed parts. This article examines and qualifies the effects of seven process parameters (melt/mold temperature, degree of foaming, injection speed, delay time, gas content, and back pressure) on biaxial bending and flexural behavior—the predominant deformation mechanisms in interior automotive applications—of foamed plaques, using the MuCell process. The results clearly show that three major factors (mold temperature, degree of foaming, and delay time) have significant impact on the mechanical properties of the foamed parts. For a clear understanding of these interactions, computed tomography scans of certain plaques are correlated to process parameters and mechanical performance. This article should forge a bridge between production and performance. © 2018 The Authors. Journal of Applied Polymer Science published by Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2019 , 136, 47275.     

Effects of different compatilizers on mechanical,crystallization and thermal properties of polypropylene/magensium oxysulfate whisker composites

Two kinds of compatilizers, maleic anhydride grafted polyolefin elastomer (POE-g-MAH) and maleic anhydride grafted polypropylene (PP-g-MAH), were incorporated into a polypropylene/magnesium oxysulfate whisker (PP/MOSw) composite. Scanning electron microscopy pictures presented a clear interface between MOSw and the PP matrix in the PP/MOSw composite, while vague interfaces appeared in the PP/iPOE-g-MAH/5MOSw and PP/iPP-g-MAH/5MOSw composites. Dynamic mechanical thermal analysis results indicated that PP-g-MAH was highly compatible with the PP matrix while POE-g-MAH was not. Impact strength results showed that POE-g-MAH had a superior toughening effect on PP/MOSw composites, since the proper interfacial interaction and appearance of β-crystal PP. However, incorporating PP-g-MAH seemed to be conducive to increasing strength and modulus (both for tensile and flexural tests), as evidenced by the greatly raised interfacial adhesion between the PP matrix and MOSw. Quantitative characterization carried out by Turcsányi equation for ternary composites also confirmed that PP-g-MAH efficiently enhanced interfacial interaction, by the proof of higher B values. Therefore, the thermal stability of PP-g-MAH treated composites was far superior to that of PP/iPOE-g-MAH/5MOSw composites. Differential scanning calorimetery and polarized light microscopy results showed that POE-g-MAH promoted PP nucleation, with effects further enhanced with the presence of PP-g-MAH.     

Fabrication of acrylic modified coconut fiber reinforced polypropylene biocomposites: Study of mechanical,thermal, and erosion properties

Coconut shell fiber‐reinforced polypropylene (PP/CSP) biocomposites were prepared by using hand lay‐out technique with different fractions of the modified fibers. Before proceeding to fabrication method, fibers were made compatible by chemical modification with acrylic acid. The interaction of acrylic modified coconut shell fibers with PP matrix was studied by using Fourier transforms Infrared spectroscopy. The morphology of chemically modified coconut fibers and coconut shell fibers reinforced polypropylene biocomposites were studied by using field emission scanning electron microscope. Due to strong interfacial interaction between PP and CSP, mechanical properties were improved. It was found that the tensile strength, elongation at break and loss modulus, rigidity of PP bio‐composites were investigated as compared with that of virgin PP matrix. The thermal properties of the fabricated biocomposites were investigated by using thermogravimetric analysis. The semi‐ductile properties of the fabricated PP biohybrids were confirmed through erosion ring test. POLYM. COMPOS., 38:2852–2862, 2017. © 2015 Society of Plastics Engineers     

Effect of morphology on the permeability,mechanical and thermal properties of polypropylene/SiO2 nanocomposites

Spherical silica nanoparticles with 20 and 100 nm diameters and organic‐template layered silica nanoparticles synthesized by the sol‐gel method were melt blended with a polypropylene (PP) matrix in order to study and quantify their effect on the oxygen and water vapor permeability and mechanical and thermal behavior. With regard to barrier properties, the spherical nanoparticles barely increased the oxygen permeability at low loads (≤10 wt%); meanwhile the layered nanoparticles dramatically increased it even at low loading (<5 wt%) probably due to the percolation effect. The changes in water vapor permeability were similar to those in oxygen permeability. The repulsive interaction between nanoparticles and PP forms interconnecting voids where the gas permeates. Tensile stress–strain tests showed that the composites present up to a 56% increase in the elastic modulus with spherical nanoparticles at 20 wt%, while layered nanoparticles show a decrease probably due to agglomerations and voids. Thermogravimetric analysis under inert conditions showed that the nanoparticles improved the PP thermal degradation process through the adsorption of volatile compounds on their surface, where the smaller spherical nanoparticles show the greatest stabilization. © 2015 Society of Chemical Industry     

Effect of pimelic acid treatment on the crystallization,morphology, and mechanical properties of isotactic polypropylene/mica composites

Pimelic acid (PA) is used as a new surface modifier for mica (MC). The effects of PA treatment on the crystallization, morphology, and mechanical properties of isotactic polypropylene (iPP)/MC composites have been investigated. FTIR analysis reveals that PA reacted with phlogopite MC, and pimelates are formed during the treatment. The results of wide angle X‐ray diffraction, differential scanning calorimetry, and polarized light microscopy prove that PA‐treated MC induces a large amount of β‐iPP and decreases the spherulite size of iPP. The results of SEM show that PA treatment improves the orientation and dispersion of MC plates in the matrix. The notched impact strength of the composites is improved dramatically by PA‐treated MC. The superior toughness is ascribed to the more ductile β spherulites, preferential orientation of MC plates, small spherulite size, and improved dispersion of MC plates in the matrix. POLYM. COMPOS., 31:1572–1584, 2010. © 2009 Society of Plastics Engineers     

Nanocomposites of silica reinforced polypropylene: Correlation between morphology and properties

Polypropylene/fumed hydrophilic silica nanocomposites were prepared via melt mixing method using a single‐screw extruder. Comparative study with and without compatibilizing copolymer agent (maleic anhydride grafted polypropylene: PP‐g‐AM) was conducted. The obtained results were interpreted in terms of silica nanoparticle–silica nanoparticle and silica nanoparticle‐polymer interactions. These results have shown that the addition of nanofillers improves the properties of the nanocomposites. From transmission electron microscopy, it was found that agglomerations of silica particles into the PP matrix increased in average size with increasing silica contents, except in presence of the copolymer. Storage modulus values of the nanocomposites measured by dynamic mechanical thermal analysis were sensitive to the microstructure of the nanocomposites. Higher silica contents resulted in higher storage modulus, revealing that the material became stiffer. By adding the compatibilizer, a further increase of storage modulus was observed due to the finer dispersion of the filler in the matrix and the increased interfacial adhesion. Crystallization rates were found to increase with the increase of silica nanoparticles as well as PP‐g‐MA content. In addition, silica nanoparticles and the compatibilizing agent present centers of germination and nucleation of crystallites. Thus, the use of the coupling agent resulted in a further enhancement of mechanical properties of the nanocomposites due to the reduction of silica agglomeration. POLYM. ENG. SCI., 54:2187–2196, 2014. © 2013 Society of Plastics Engineers