Effects of cooling rates on crystallization behavior and melting characteristics of isotactic polypropylene as neat and in the TPVs EPDM/PP and EOC/PP

Non-isothermal crystallization behavior and melting characteristics of polypropylene (PP) in EPDM/PP and EOC/PP TPVs were studied at various cooling rates using differential scanning calorimetry (DSC). The results revealed that the crystallization of PP in the TPVs occurs at a lower degree of undercooling, relative to neat PP, with smaller size PP crystals. The vulcanized EPDM and EOC particles could accelerate the crystallization of the PP phase either by providing nucleation or by promoting interfacial crystallization. The crystallization exotherm and melting endotherm peaks of the TPVs were broad, and they shifted towards lower temperatures as the cooling rate was increased. The analysis of non-isothermal crystallization kinetics indicates that the crystallization of the PP in the TPVs is heterogeneous nucleation, with two or three-dimensional growth during primary and secondary crystallization. Furthermore, the vulcanized EPDM and EOC particles promote the initial crystallization activation energy of the PP in TPVs to exceed that of the neat PP. The developed mathematical models show an approximately power-law dependence on the cooling rate for the crystallization behavior and the melting characteristics of PP in the TPVs.     

Intumescent flame retardation and silane crosslinking of PP/EPDM elastomer

This study deals with the silane crosslinking and intumescent flame retardation of polypropylene/ethylene‐propylene‐diene copolymer (PP/EPDM) elastomers. The effect of silane crosslinking on the flame retardancy of the PP/EPDM composites containing melamine phosphate (MP) and dipentaerythritol (DPER) was studied by limiting oxygen index, UL 94 and cone calorimetry tests. The chemical composition of the silane crosslinked and flame retarded PP/EPDM composites treated at different temperatures was studied by X‐ray photoelectron spectroscopy and real time Fourier transform infrared (FTIR) spectrometry. Thermal decomposition and crystallization behavior of the PP/EPDM composites were investigated using thermogravimetric analysis and differential scanning calorimetry, respectively. Moreover, the mechanical properties of the composites were also studied. It is found that the flame retardancy, mechanical properties, and thermal decomposition behavior of the composites are influenced by silane grafting and crosslinking. Copyright © 2008 John Wiley & Sons, Ltd.     

Synergistic effects of cerium phosphate and intumescent flame retardant on EPDM/PP composites

An intumescent flame retardant system composed of ammonium polyphosphate (APP) and pentaerythritol (PER) was used for flame retarding ethylene–propylene–diene‐modified elastomer (EPDM)/polypropylene (PP) blends. Cerium phosphate (CeP) was synthesized and the effect on flame retardancy and thermal stability of EPDM/PP composites based on intumescent flame retardant (IFR) were studied by limiting oxygen index (LOI), UL‐94, and thermogravimetic analysis (TGA), respectively. Scanning electron microscopy (SEM) and Fourier transform infrared spectrometry (FTIR) were used to analyze the morphological structure and the component of the residue chars formed from the EPDM/PP composites, and the mechanical properties of the materials were also studied. The addition of CeP to the EPDM/PP/APP/PER composites gives better flame retardancy than that of EPDM/PP/APP/PER composites. TGA and RT‐FTIR studies indicated that an interaction occurs among APP, PER, and EPDM/PP. The incorporation of CeP improved the mechanical properties of the materials. Copyright © 2010 John Wiley & Sons, Ltd.     

Prediction models for the key mechanical properties of EPDM/PP blends as affected by processing parameters and their correlation with stress relaxation and phase morphologies

The optimum condition of processing parameters (mixing temperature, rotor speed, fill factor, and blend ratio) and prediction models for the best key mechanical properties of ethylene propylene diene terpolymer/polypropylene thermoplastic vulcanizates (EPDM/PP TPVs) was investigated by using the Taguchi's optimization technique and data analysis. The results reveal that all of the processing parameters affected significantly the mechanical properties of the EPDM/PP TPVs, but specifically the blend ratio contributed more than 90% in effect size on tensile strength and tension set. There were three main factors, the mixing temperature, the fill factor, and the blend ratio, influencing the elongation at break. Furthermore, the mathematic models were effective and reliable in predicting the properties of TPVs. The correlation of mechanical properties, stress relaxation, and phase morphologies of the TPVs prepared from the predicted models was also investigated. It can be summarized that the morphological structure and stress relaxation of the TPVs were strongly governed by the EPDM content in the blend ratio. That is, the higher the EPDM content, the better phase morphology having smaller size of the vulcanized EPDM particles distributed in the PP matrix and the higher rate of stress relaxation. Moreover, these two properties were then principally pushing the mechanical characteristics of the EPDM/PP TPVs. Copyright © 2015 John Wiley & Sons, Ltd.     

Synergistic effects of layered double hydroxide with phosphorus-nitrogen intumescent flame retardant in PP/EPDM/IFR/LDH nanocomposites

<正>Synergistic effects of layered double hydroxide(LDH) with intumescent flame retardanct(IFR) of phosphorus-nitrogen (NP) compound in the polypropylene/ethylene-propylene-diene/IFR/LDH(PP/EPDM/IFR/LDH) nanocomposites and related properties were studied by X-ray diffraction(XRD),transmission electron microscopy(TEM),scanning electron microscopy(SEM),limiting oxygen index(LOI),UL-94 test,cone calorimeter test(CCT) and thermo-gravimetric analysis (TGA).The XRD and TEM results show that the intercalated and/or exfoliated nanocomposites can be obtained by direct melt-intercalation of PP/EPDM into modified LDH and that LDH can promote the IFR additive NP to disperse more homogeneously in the polymer matrix.The SEM results provide positive evidence that more compact charred layers can be obtained from the PP/EPDM/NP/LDH sample than those from the PP/EPDM/LDH and PP/EPDM/NP samples during burning.The LOI and UL-94 rating tests show that the synergetic effects of LDH with NP can effectively increase the flame retardant properties of the PP/EPDM/NP/LDH samples.The data from the CCT and TGA tests indicate that the PP/EPDM/NP/LDH samples apparently decrease the HRR and MLR values and thus enhance the flame retardant properties and have better thermal stability than the PP/EPDM/LDH and PP/EPDM/NP samples.     

Preparation of polypropylene/ethylene‐propylene‐diene terpolymer/nitrile rubber ternary thermoplastics vulcanizates with good mechanical properties and oil resistance by core‐shell dynamic vulcanization

As the most successful commercialized thermoplastic vulcanizates (TPVs), polypropylene (PP)/ethylene propylene rubber (EPDM) TPVs exhibit poor oil resistance. In this work, we prepared PP/EPDM/butadiene acrylonitrile rubber (NBR) ternary TPVs with good oil resistance using core‐shell dynamic vulcanization. According to the theoretical analysis of the spreading coefficient and the transmission electron microscopy results, the rubber phases exhibited a special core‐shell structure, in which the cross‐linkedNBR‐core was encapsulated by the EPDM‐shell. The core‐shell structure effectively improved the interfacial compatibility between PP and NBR phase as the EPDM‐shell could avoid the direct contact of them, thus improving the mechanical properties of the TPVs. For example, the PP/EPDM/NBR (40/30/30) ternary TPV showed enhanced tensile strength of 12.57 MPa, compared with 10.71 MPa of PP/EPDM (40/60) TPV and 11.11 MPa of PP/NBR (40/60) TPV, respectively. Moreover, the oil resistance of the TPVs was also improved. Compared with PP/EPDM TPV, the change rates in mass, volume, tensile strength and elongation at break of PP/EPDM/NBR TPV after oil immersion decreased by 42.18%, 48.69%, 52.68% and 28.77%, respectively.     

Mechanical properties and morphological structures of short glass fiber reinforced PP/EPDM composite

The mechanical properties and crystal morphological structures of short glass fiber (SGF) reinforced dynamically photo-irradiated polypropylene (PP)/ethylene-propylene-diene terpolymer (EPDM) composites were studied by mechanical tests, wide-angle X-ray diffraction (WAXD), optical microscopy, scanning electron microscopy (SEM), differential scanning calorimetry (DSC), and thermogravimetric analyzer (TGA). The mechanical properties of PP/EPDM composites, especially the tensile strength were greatly strengthened by dynamically photo-irradiation and the incorporation of SGF. The results from the WAXD, SEM, DSC, and TGA measurements reveal: (i) the formation of β-type crystal of PP in the PP/EPDM/SGF composite; (ii) the fiber length in dynamically photo-irradiated PP/EPDM/SGF composites are general longer than that in corresponding unirradiated samples. The size of EPDM phase in the photo-irradiated composites reduces obviously whereas the droplet number increases; (iii) photo-irradiation improves the interface adhesion between SGF and polymer matrix; (iv) the melting and crystallization temperatures of the photo-irradiated composites are not affected greatly by increasing the SGF content; (v) the thermal analysis results show that the incorporation of SGF into PP/EPDM plays an important role for increasing its thermal stability.     

Design of PP/EPDM/NBR TPVs with tunable mechanical properties via regulating the core-shell structure

In this work, polypropylene (PP)/ethylene-propylene-diene monomer (EPDM)/butadiene acrylonitrile rubber (NBR) TPVs with different EPDM/NBR ratios were prepared by the core-shell dynamic vulcanization. The relationship between the core-shell structure and mechanical properties of the TPVs were thoroughly investigated. The formation of core-shell structure by adding NBR is conducive to the mechanical properties of the TPVs. The ratio of EPDM to NBR has an important effect on the structure and performances of the final products, and there is a critical ratio for this effect change. Transmission electron microscope (TEM), tensile test, reprocessing test, ageing test, rheological behavior test and stress relaxation were used to characterize the morphology and properties of the TPVs in detail. It was found that when the ratio of EPDM/NBR was 2:4, the tensile strength increased by ~14% compared with PP/EPDM TPV without NBR. Meanwhile, the reprocessing properties, rheological characteristics and instantaneous tensile deformation, etc. all exhibited sudden changes at this critical ratio.     

Electrical insulation performance of flame retardant fillers filled with polypropylene/ethylene propylene diene monomer composites

Flame retardant fillers composed of zinc hydroxy stannate (ZHS), calcium borates (CaB), and NP‐100 were embedded separately in 50% polypropylene (PP) and 50% ethylene propylene diene monomer (EPDM) blends. Several formulations containing flame retardant fillers, PP, and EPDM were prepared using an internal mixer and were molded in a compression mold to form test samples. The effects of filler loading (15, 30, 45, and 60 vol%) on the dielectric breakdown strength and contact angle were determined. It was found that PP/EPDM/NP‐100 has higher breakdown strength than PP/EPDM/ZHS and PP/EPDM/CaB. The contact angle of PP/EPDM/NP‐100 and PP/EPDM/ZHS showed an ascending order with filler loading, implying an increase in hydrophobicity. With regard to the PP/EPDM/CaB system, the contact angle showed an ascending order up to 30 vol% followed by a descending order at 45–60 vol%. Water absorption studies indicated that PP/EPDM/NP‐100 has lower water absorption compared with PP/EPDM/ZHS and PP/EPDM/CaB. PP/EPDM filled with 15 vol% NP‐100 was found to exhibit interesting insulating properties in comparison with other composite systems, thanks to high breakdown voltage, good hydrophobicity, and low water absorption. Copyright © 2014 John Wiley & Sons, Ltd.     

Polypropylene composites filled by magnesium hydroxide coprecipitated with foreign ions

Rod‐like magnesium hydroxide (MH) particles were prepared via coprecipitation of the magnesium salt with foreign ions, such as copper(II), zinc(II), iron(III), and nickel(II). Flame retardant polypropylene (PP) composites were fabricated using these particles. The microstructure, flame retardation, mechanical properties, thermal behavior, and oxidation‐induced temperature were characterized. It was found that foreign ion compounds increased the flame retardancy. MH containing a zinc compound presented a similar performance as that of neat MH. The presence of a copper compound decreased the thermal behavior and mechanical properties of the flame retardant composite, while iron and nickel compounds brought some improvements. In addition, the thermal degradation mechanisms of the flame retardant composites were investigated by Fourier transform infrared (FTIR) spectroscopy at different temperatures. Copyright © 2008 John Wiley & Sons, Ltd.     

Influence of Fe‐MMT on the fire retarding behavior and mechanical property of (ethylene‐vinyl acetate copolymer/magnesium hydroxide) composite

In this work, Fe‐montmorillonite (Fe‐MMT) is synthesized and used as a synergistic agent in ethylene vinyl acetate/magnesium hydroxide (EVA/MH) flame retardant formulations. The synergistic effect of Fe‐MMT with magnesium hydroxide (MH) as the halogen‐free flame retardant for ethylene vinyl acetate (EVA) is studied by thermogravimetric analysis (TGA), limiting the oxygen index (LOI), UL‐94, and cone calorimetry test. Compared with that of Na‐MMT, it indicates that the synergistic effects of Fe‐MMT enhance the LOI value of EVA/MH polymer and improve the thermal stability and reduce the heat release rate (HRR). The structure and morphology of nanocomposites are studied by X‐ray diffraction (XRD) and transmission electron microscopy (TEM). The mechanical properties of the EVA composites have also been studied here, indicating that the use of Fe‐MMT reduces the amount of inorganic fillers. MH hence enhances the mechanical properties of the EVA composite while keeping the UL‐94 V‐0 rating. Copyright © 2008 John Wiley & Sons, Ltd.     

Preparation and characterization of vinyltriethoxysilane grafted ethylene propylene diene terpolymer/linear low density polyethylene (EPDM‐g‐VTES/LLDPE) blends

Graft polymerization of vinyltriethoxysilane (VTES) onto ethylene‐propylene‐diene terpolymer (EPDM) was carried out in toluene using dicumylperoxide (DCP) as initiator. Effects of various parameters (EPDM content, VTES content, reaction time, reaction temperature and initiator concentration) on the grafting efficiency of VTES onto EPDM were investigated. At the optimum grafting efficiency conditions, EPDM‐g‐VTES was developed by melt mixing in a twin screw extruder and then linear (l), statically vulcanized (s) and dynamically vulcanized (d) blends of EPDM‐g‐VTES with linear low‐density polyethylene (LLDPE) with varying percentage compositions were prepared by melt mixing in the twin screw extruder. The grafting of VTES onto EPDM and its crosslinking was confirmed by FT‐IR. The characterization of mechanical properties such as tensile strength, elongation at break, Young's modulus and hardness, differential scanning calorimetry (DSC) analysis and morphology were studied and compared for the EPDM‐g‐VTES/LLDPE blends. The study reveals that the dynamically vulcanized blend improves the mechanical and thermal properties due to the presence of efficient interaction between component polymers when compared with other blends. Copyright © 2005 John Wiley & Sons, Ltd.     

Effect of ethylene-acrylic acid copolymer on flame retardancy and properties of LLDPE/EAA/MH composites

Halogen-free flame retardant linear low density polyethylene (LLDPE)/ethylene-acrylic acid copolymer (EAA) blends were prepared in a melt process using magnesium hydroxide (MH) as flame retardant. The effect of EAA on flame retardancy and properties of LLDPE/EAA/MH composites was studied. The flammability of composites was investigated using Limiting Oxygen Index (LOI) and Cone calorimeter test. The results showed that the introduction of EAA into composites apparently increased LOI from 28% to 39%, meanwhile, reduced heat release rate (HRR) and smoke production rate (SPR) according to Cone calorimeter results, which was mainly due to the uniform dispersion of MH as a result of hydrogen bonding and acid-base reaction between MH and EAA. This improved interfacial adhesion was confirmed by Scanning Electronic Microscopy (SEM). Thermogravimetric analysis (TGA) showed that EAA could enhance the thermal oxidative stability of composites. It was attributed to the formation of a stable barrier to prevent the heat and mass transfer in fire, which was confirmed by the observation of fire performance with Cone calorimeter. The crystallization and rheological behaviour of composites were studied using Differential scanning calorimeter (DSC) and oscillatory rheological measurements. Mechanical test results indicated that the addition of EAA could increase the elongation at break and impact strength of composites.     

Preparation of Intumescent Flame Retardant Polypropylene composite through Solid State Mechanochemical Method

Polypropylene (PP), with characteristics of good mechanical properties, good resistance to water and low cost, has been widely used in many fields such as building, transport, furniture and electrical industries. However, a fateful drawback of polypropylene is its high flammability,restricting its wider applications. Addition of flame retardants is an effective way to improve its flame retardancy. An effective halogen-free flame retardant system used is the mixture of melamine, ammounium phosphate and pentaerythritol (intumescent flame retardant). But how to enhance the dispersion of this mixture in polypropylene matrix is a big problem. A self-made mechanochemical reactor, pan type milling equipment, can exert strong shear and squeeze forces,and has good mixing function. As a result, a uniform dispersion of flame retardants in the polymer matrix can be expectably obtained by using this equipment.In this paper, flame-retarded Polypropylene (PP) composites with intumescent flame retardant (IFR) were prepared via solid state mechanochemical method (pan-mill) and conventional method (twin-roll masticator) respectively. Particle diameter analysis, melt flow index (MFI), differential scanning calorimetry (DSC) and scanning electronic microscopy (SEM) were used to characterize these composites, and the mechanical properties and flame retardancy were also determined. The experimental results showed that the blend of PP and IFR were effectively pulverized from 3～4 mm to less than 300i m under the strong shear forces of pan-mill. With increasing the milling cycles, the MFI value of IFR/PP blend decreased first and then increased. The mechanical properties and flame retardancy of IFR/PP blends prepared by solid state mechanochemical method were proved to be better than those prepared by conventional method because of the dispersing function of pan-mill.Also it was found that IFRs were the nucleating agent for PP and the crystallinity of PP increased first and then decreased with increasing the milling cycles.     

Effect of Phosphorus-Nitrogen Intumescent Flame Retardant on Structure and Properties of Poly(propylene)

Summary : Phosphorus-nitrogen intumescent product (R₂₀₀₀) was filled into polypropylene (PP) as a flame retardant. The neat PP and flame-retarded PP blends were studied for their structural and mechanical properties after verification of the flame retardancy character of blends. In this paper, the influence of incorporation of different amount (5%, 10%, 15%, 20%, and 25%) of R₂₀₀₀ was studied. The flame retardancy is evaluated by limiting oxygen index (LOI) value, which is enhanced from 17.5 for pure PP to 22.7 for the blend comprising 15% intumescent product, phosphorus-nitrogen based (R₂₀₀₀). The thermal degradation behaviour of the PP/R₂₀₀₀ blends was investigated using thermogravimetric analysis (TGA) under nitrogen (N₂) and oxygen (O₂) atmospheres. The influence of the R₂₀₀₀ on the PP crystallization was examined by X-ray diffraction (XRD) and differential scanning calorimetry (DSC). Further, the mechanical properties of the materials were studied by dynamic mechanical analysis (DMA). The incorporation of the flame retardant had no effect on the crystallization of the neat polymer and the mechanical properties of the materials remained unaffected.     

乙丙橡胶/聚丙烯共混体系的界面相互渗透

本文用X射线衍射仪、差热分析仪、动态力学扭摆仪和测定有效网链密度等方法,研究了乙丙橡胶/聚丙烯(EPDM/PP)共混体系中PP的非晶部分和EPDM的相互渗透。EPDM和PP不具有互溶性,但PP的非晶部分和EPDM两相界面处有较强的相互渗透,即部分互容性。有效链密度和性能间关系的数据表明,共混体系不一定存在硫化胶那样的对应关系。     

Mechanical and Rheological Behavior of Unvulcanized and Dynamically Vulcanized i-PP/EPDM Blends

The mechanical and rheological behavior of dynamically vulcanized PP/EPDM blends is examined and compared with those of unvulcanized blends. The effect of blend ratio and dynamic vulcanization of EPDM rubber on tensile properties and flow are investigated. The mechanical properties of the blends are strongly influenced by the blend ratio. With the increasing of EPDM content the value of yield stress in a solid state decreases with the elastomer volume fractions less than 0.45 for the unvulcanized blends. For the dynamically vulcanized blends the interval of EPDM content, at which the yield peak is seen, is rather limited below 0.25 elastomer volume fractions. It is shown that dynamic vulcanization changes the deformational behavior of PP/EPDM blends. The rheological properties of dynamically vulcanized blends depending on the ratio of the components may be similar to the properties of polymer composites containing the highly disperse structuring filler. The distinction between the rheological behavior of unvulcanized and dynamically vulcanized blends is related to differences of their structures and viscoelastic characteristics of unvulcanized and vulcanized EPDM phase.     

Effect of β-phase on the fracture behavior of dynamically vulcanized PP/EPDM blends studied by the essential work of fracture approach

The effect of β phase polypropylene (PP), induced by β-nucleating agent (β-NA), on the fracture behavior in dynamically vulcanized thermoplastic elastomers (TPVs) based on dynamically vulcanized PP/ethylene-propylene-diene rubber (EPDM) blend was studied. Differential Scanning Calorimetry (DSC) and Wide-angle X-ray diffraction (WAXD) were employed to study the melting behavior and crystalline structures, and the results indicated that the β-NA induced β phase of PP effectively in TPVs. With the increasing dosage of the β-NA incorporated in, the content of β phase increased while the total crystallinity of the blend kept constant. The fracture behavior of the TPVs with different β phase content was studied with double edge notched tensile loaded specimens (DENT) using the essential work of fracture (EWF) approach. The specific essential work of fracture (w_e) increased with the increasing of β phase content, indicating that the presence of β phase could effectively enhance the fracture toughness of TPVs.     

A new intumescent flame‐retardant: preparation,surface modification,and its application in polypropylene

Melamine salt of tripentaerythriol phosphate (MTP), as a new intumescent flame‐retardant, was prepared from tripentaerythritol (TPE), polyphosphoric acid, phosphoric pentoxide, and melamine, and then incorporated into polypropylene (PP) to obtain flame‐retarded PP‐MTP. FT‐IR analysis showed that MTP was in the form of cage structure. The flammability, combustion behavior, and thermal degradation and stability of flame‐retarded PP were characterized by using LOI, UL‐94 test, cone calorimetry, and TGA, respectively. By SEM, the char structure of PP‐MTP was analyzed. XRD diffraction tests showed that PP‐matrix of PP‐MTP presented better crystallized phases, when MTP was modified by methyl hydrogen siloxane. The relations of the dispersion of MTP in PP matrix to the compatibility between PP and MTP, and to the flame retardancy were discussed. Copyright © 2008 John Wiley & Sons, Ltd.     

Synthesis of a novel polyphosphazene/triazine bi‐group flame retardant in situ doping nano zinc oxide and its application in poly (lactic acid) resin

A novel polyphosphazene/triazine bi‐group flame retardant in situ doping nano ZnO (A4‐d‐ZnO) was synthesized and applied in poly (lactic acid) (PLA). Fourier transform infrared (FTIR), solid state nuclear magnetic resonance (SSNMR), X‐ray photoelectron spectroscopy (XPS), scanning electron microscope (SEM), transmission electron microscope (TEM), and energy dispersive spectrometer (EDS) were used to confirm the chemical structure of A4‐d‐ZnO. The thermal stability and the flame‐retardant properties of the PLA composites were characterized by thermogravimetric analysis (TGA), differential scanning calorimetry (DSC), limiting oxygen index (LOI), vertical burning test (UL‐94), and micro combustion calorimeter (MCC) test. The results of XPS showed that A4‐d‐ZnO has been synthesized, and the doping ratio of ZnO was 7.2% in flame‐retardant A4‐d‐ZnO. TGA results revealed that A4‐d‐ZnO had good char forming ability (40 wt% at 600°C). The results of LOI, vertical burning test, and MCC showed that PLA/5%A4‐d‐ZnO composite acquired a higher LOI value (24%), higher UL94 rating, and lower pk‐HRR (501 kW/m²) comparing with that of pure PLA. It indicated that a small amount of flame‐retardant A4‐d‐ZnO could achieve great flame‐retardant performance in PLA composites. The catalytic chain scission effect of A4‐d‐ZnO could make PLA composites drip with flame and go out during combustion, which was the reason for the good flame‐retardant property. Moreover, after the addition of A4‐d‐ZnO, the impaired mechanical properties of PLA composites are minimal enough.