Rheological characteristics of blends of isotactic polypropylene with high density polyethylene

Binary blends of iPP/HDPE have been prepared in order to evaluate the effect of the ratio of the viscosities of the parent polymers on the rheological behaviour of the blends. The viscosity of a blend is intermediate when the viscosities of the homopolymers are very different; a slight minimum occurs when the viscosity ratio is near to one. Some tests have also been performed on an iPP/LDPE blend generally confirming these results without peculiarities due to the branching. The die-swell values of the blends are intermediate, also when the values for the parent polymers are similar. For the critical shear rate, a maximum occurs when the critical shear rate of the polyethylene is larger than that of the polypropylene.     

CRYSTALLIZATION AND MECHANICAL PROPERTIES OF BLENDS OF METALLOCENE SHORT CHAIN BRANCHED POLYETHYLENE WITH CONVENTIONAL POLYOLEFINS

Metallocene-catalyzed short chain branched polyethylene (SCBPE) was blended with LDPE, HDPE, PS, EPDM and iPP in the weight proportions of 80 and 20. The crystallization and mechanical properties of these blends were studied by PLM, DSC and DMA. It has been observed in PLM that SCBPE/LDPE, SCBPE/HDPE and SCBPE/EPDM can form band spherulites whose band width and size are both smaller than that of the pure SCBPE. Tiny crystallites are observed in the completely immiscible SCBPE/PS blend. The crystallites in SCBPE/iPP are very small and only irregular spherulites are seen. The crystallization kinetics and mechanical properties of SCBPE are greatly affected by the second polyolefin, but in a different way, depending on the phase behavior and the modulus of the second components. SCBPE may be phase miscible in the melt with HDPE, LDPE and EPDM and co-crystallize together with HDPE or LDPE during cooling. A big change of crystal morphology and crystallization kinetics is seen in SCBPE/iPP blend compared with pure SCBPE and the lowest tanδ is also seen for this system. DMA results show that the tensile modulus of the blends has nothing to do with phase behavior, but only depends on the modulus of the second component.     

PP/LDPE共混体系的辐射效应

研究了在多官能团单体—三烯丙基异氰脲酸酯存在下ＰＰ／ＬＤＰＥ共混体系接受γ－辐射的效果。用溶解度参数和ＴＥＭ技术评估了共混体系的相容性与多官能团单体在共混体系中的分布，并用ＳＥＭ、ＤＳＣ、动态力学等方法对共混体系相容性进行了表征。结果表明，ＰＰ／ＬＤＰＥ是不相容的共混体系，三烯丙基异氰脲酸酯主要分布在共混体系的相界面区域，辐照强化了共混体系的相间结合，增加了界面厚度，改善了共混体系的相容性。     

Evolution of products during the degradation of polyethylene in a batch reactor

The thermal degradation of two polyethylene samples (LDPE and HDPE) has been carried out in a batch reactor under dynamic conditions. The evolution of products generated after regular intervals of 5 min (temperature increments of approximately 25 °C) has been analyzed. The behaviour of LDPE and HDPE has been compared, and no differences in the quantity and weight fraction of the gaseous products obtained have been found. For both polymers, n-paraffins are the major products at the very beginning of the process, while as the decomposition proceeds 1-olefins are more abundant. The condensed fraction is much larger than the gaseous fraction and its analysis reveals some differences between the behaviour of LDPE and HDPE at the beginning of the degradation process. These differences disappear at higher temperatures where more similar trends are observed. 1-Olefins, n-paraffins, dienes and olefins with wide carbon number distributions are the most important condensed compounds obtained in the thermal degradation of both polyethylenes. The formation of 1-olefins and n-paraffins begins at slightly lower temperatures than for dienes and olefins. On the other hand, as the temperature increases, the amount of low and high molecular weight compounds increases at the expense of intermediate molecular weight products and the former become the most important by the end of the degradation process. This behaviour could be related to the thermal cracking of waxes through secondary reactions.     

Properties of Low Density Polyethylene/Polypropylene Blends

ABSTRACT

The role of di-cumyl peroxide (DCP) as compatibilizer in low density Polyethylene/Polypropylene (LDPE/PP) blends has been explored. Mixtures with varying LDPE/PP ratio were prepared in a Brabender plasticorder and tested for their mechanical properties and calorimetric response. Then peroxide was added at concentrations up to 0.5%, and the mechanical properties of the these new blends were measured. Also, the mixing torque, melt flow index and gel content of the above products were recorded as a function of peroxide concentration. It was found that the incorporation of DCP restricts the thermoplastic characteristics of the melt, which was primarily attributed to branching which occurs in LDPE. This results in an enhancement in the adhesive bonding between the two polymers mainly due to chain entanglements. This was further supported by the fact that mechanical properties of the treated blend were significantly improved.     

Polymer blends based on the β-modification of polypropylene

iPP/sPP, iPP/rPP, iPP/PVDF and iPP/PA-6 blends, and their β-nucleated forms were prepared in the present study. The components of iPP/sPP and iPP/rPP blends are compatible in the molten state. The phase structure of the melt of iPP/PVDF and iPP/PA-6 blends is heterogeneous. The melting and crystallisation characteristics as well as the structure and polymorphic composition of these blends were studied by polarised light microscopy (PLM) and differential scanning calorimetry (DSC). When semicrystalline polymers are added to iPP, the most important factor of the formation a blend with β-crystalline phase is the α-nucleation effect of the second polymer. In the case of polymers with an α-nucleating effect, the temperature range of their crystallisation should be lower than that of β-iPP. β-nucleated iPP/PVDF and iPP/PA-6 blends are extreme examples showing that completely β-iPP matrix can not form even in the presence of a highly effective β-nucleant, because of the strong α-nucleating ability and higher crystallisation temperature range of PVDF and PA-6. We found that the β-crystallisation tendency of random propylene copolymers can be enhanced by adding an iPP homopolymer.     

间规聚苯乙烯/等规聚丙烯/间规聚苯乙烯-b-聚(1-丁烯)共混体系相容性

间规聚苯乙烯(sPS)的改性主要是对其增韧改性,提高其力学性能.sPS的化学改性已有较多文献报道[1,2].     

A novel zinc chelate complex containing both phosphorus and nitrogen for improving the flame retardancy of low density polyethylene

A novel metal chelate complex containing phosphorus, nitrogen and zinc (II) ion was synthesized and used as the flame retardant of low density polyethylene (LDPE). The zinc chelate complex was synthesized by reacting zinc acetate with the ligand of tetraethyl (1,2-phenylenebis(azanediyl)) bis (2-hydroxylphenylmethylene) diphosphonate (TEPAPM). The chemical structure of the target Zn-TEPAPM was confirmed by FTIR, ¹H NMR, ¹³C NMR and ³¹P NMR spectra. The flame retardancy and thermal behavior of LDPE containing various amount of Zn-TEPAPM were investigated by limiting oxygen index test, thermogravimetric (TG) analysis and cone calorimetry. The results show that Zn-TEPAPM can greatly increase the thermal stability, the char formation and smoke suppression ability of LDPE. The TG curves show that even when the filler content of Zn-TEPAPM is as low as 1 wt% in LDPE, the onset degradation temperature of LDPE is increased from 429 °C to 442 °C, and the maximum degradation temperature is increased from 469 °C to 488 °C. Also, a reduction of 32% for the peak heat release rate (PHRR) is obtained in the cone test. Moreover, Zn-TEPAPM is demonstrated to be a very effective synergist of ammonium polyphosphate (APP). When 1 wt% of Zn-TEPAPM was introduced into the LDPE/APP (mass ratio 80/19) blend, the PHRR value is reduced by 32%, compared with that of LDPE/APP blend without Zn-TEPAPM, and the char layer becomes more compact and intact.     

Morphology and thermal degradation studies of melt-mixed poly(lactic acid) (PLA)/poly(ε-caprolactone) (PCL) biodegradable polymer blend nanocomposites with TiO2 as filler

The morphology and thermal stability of melt-mixed poly(lactic acid) (PLA)/poly(ε-caprolactone) (PCL) blend nanocomposites with small amounts of TiO₂ nanoparticles were investigated. The nanoparticles were mostly located in the PLA phase, with good dispersion of individual particles, although significant aggregation was also visible. The thermal stability and degradation behaviour of the different samples were studied using thermogravimetric analysis (TGA) and TGA-Fourier-transform infrared (FTIR) spectroscopy. Neat PCL showed better thermal stability than PLA, but the degradation kinetics revealed that PLA had a higher activation energy of degradation than PCL, indicating its degradation rate more strongly depends on temperature, probably because of a more complex degradation mechanism based on chain scission and re-formation. Blending of PLA and PCL reduced the thermal stabilities of both polymers, but the presence of TiO₂ nanoparticles improved their thermal stability. The nanoparticles also influenced the volatilization of the degradation products from the blend, acted as degradation catalyst and/or retarded the escape of volatile degradation products.     

Conducting films of poly(aniline‐co‐1‐amino‐ 2‐naphthol‐4‐sulfonic acid) blended with LDPE for its application as antistatic encapsulation material

The paper presents the electrostatic charge dissipative (ESD) properties of the conducting copolymers of aniline (AN) and 1‐amino‐2‐naphthol‐4‐sulfonic acid (ANSA) blended with low‐density polyethylene (LDPE). The copolymers of aniline and ANSA were synthesized under different reaction conditions. Blending of copolymers with LDPE was carried out in twin screw extruder by melt blending method by loading 0.5 and 1.0 wt% of the conducting copolymer in LDPE matrix. The mechanical properties of the blended films depend on the incorporation of copolymer in the LDPE matrix. The morphology of copolymer–LDPE blend was studied by scanning electron microscopy. The conductivity of the blown film of poly(AN‐co‐ANSA)/LDPE blend was found to be in the range of 10^?6–10^?11 S/cm, showing its potential use as antistatic bag for the encapsulation of electronic equipments. The static decay time of the film was found to be of the order of 0.1–1.9 sec on recording the decay time from 5000 to 500 V. Static charge measurements carried out on the films show that no charge is present on the surface. The level of interaction between the copolymers and the matrix polymer was determined by the FTIR spectra, blend morphology, electrical conductivity, and thermal analysis. The effect of the morphology on electrical and antistatic behavior of copolymers has also been investigated. Copyright © 2009 John Wiley & Sons, Ltd.     

Pyrolysis mass spectrometry analysis of poly(vinyl acetate), poly(methyl methacrylate) and their blend coalesced from inclusion compounds formed with γ-cyclodextrin

Direct insertion probe pyrolysis mass spectrometry (DIP-MS) analyses of poly(methyl methacrylate) (PMMA), poly(vinyl acetate) (PVAc) and binary PMMA/PVAc guests, coalesced from their inclusion compounds (ICs) formed with host γ-cyclodextrin (γ-CD) through removal of the γ-CD host, have been performed. A slight increase in the thermal stabilities of the coalesced polymers were recorded both by TGA and DIP-MS compared to the corresponding as-received polymers. The DIP-MS observations pointed out that the thermal stability and degradation products of these polymers are affected once they are included inside the IC channels created by the stacked host γ-CDs. DIP-MS observations suggested that the degradation mechanisms for PMMA and PVAc chains in their coalesced blend were significantly altered from those observed in their as-received and solution blended samples. This was attributed to the presence of specific molecular interactions between the intimately mixed PMMA and PVAc chains in their coalesced blend.     

Starch plasticized with glycerol from biodiesel and polypropylene blends

Plastics have been used in short-life products, which have presented harmful consequences for the nature, due to the low degradation rate reached by the most common polyolefins, such as the polypropylene. By this way, the incorporation of pro-oxidants has been shown nice results to the bio-assimilation of the common polymers. The aim of this study is to evaluate the mechanical and thermal properties of pure iPP, plasticized starch (TPS) with biodiesel glycerol (TPS_Bio) or commercial glycerol (TPS_Com), and their blends (iPP/TPS_Plas). TPS was plasticized in proportions of 80/20 (wt starch/wt glycerin). Blends of iPP/TPS_Plas were obtained by extrusion in the following composition rates: 95/5, 90/10, 80/20, and 70/30 of modified PP/TPS_Plas. Mechanical properties, calorimetric analysis, and thermogravimetric data were obtained, and biodegradation under simulated soil was performed. It can be verified that there were no meaningful variation induced by the incorporation of TPS_Plas on the melting temperature on the blends, when compared to pure iPP. The addition of TPS_Plas caused an increasing on the crystallinity of iPP, mainly for the compositions 90/10 and 80/20 of iPP/TPS_Plas, probably due a morphological alteration such as crosslinking, which may have modified the molecular arrangement of the iPP macromolecules by the presence of glycerol, which was also indicated by mechanical evaluations.     

Epitaxial crystallization and oriented structure of linear low‐density polyethylene/isotactic polypropylene blends obtained via dynamic packing injection molding

In this work, as a part of a long‐term project aimed at controlling of crystal structure and phase morphology for a injection molded product, we investigated the oriented structure and possible epitaxial growth of polyolefin blend (low‐density polyethylene (LLDPE)/isotatic polypropylene (iPP)), achieved by dynamic packing injection molding, which introduced strong oscillatory shear on the gradually‐cooled melt during the packing process. The crystalline and oriented structures of the prepared blends with different compositions were estimated in detail through 2D X‐ray diffraction, calorimetry, and optical microscopy. As iPP was the dominant phase (its content was more than 50 wt%), our results indicated that it could be highly oriented in the blends. In such case, it was interesting to find that LLDPE epitaxially crystallized on the oriented iPP through a crystallographic matching between (100)_LLDPE and (010)_iPP, resulting in an inclination of LLDPE chains, about 50° to the iPP chain axis. On the other hand, as iPP was the minor phase, iPP was less oriented and no epitaxial growth between iPP and LLDPE was observed; even LLDPE remained oriented. The composition‐dependent epitaxial growth of LLDPE on oriented iPP could be understood as due to: (1) the effect of crystallization sequence, it was found that iPP always crystallized before LLDPE for all compositions; (2) the dependence of oriented iPP structure on the blend composition; (3) the “mutual nucleation” between LLDPE and iPP due to their partial miscibility. Copyright © 2009 John Wiley & Sons, Ltd.     

Degradation of polymer blends—Part XI. Blends of polystyrene with polyisoprene

The degradation behaviour of polystyrene and cis-1,4-polyisoprene when both are present in the same film as a 1:1 blend has been compared with that when the polymers are degraded separately. Degradations have been studied under programmed heating conditions using TG, TVA, DTA and DSC and also under isothermal conditions at 340 and 360°C. Volatile products of degradation have been studied and separated by sub-ambient TVA and also identified by spectroscopic methods. The volatile products from the blend are the same as those from the constituent polymers. Volatile production occurs less readily for each polymer than when it is degraded alone. Stabilisation of PS is especially marked and under isothermal conditions at the above temperatures, PS does not evolve volatiles until PI degradation is completed. Chain scission in PS, prior to volatilisation, is increased, however, in the presence of PI. It is concluded that the increased scission results from attack on PS by PI radicals of short chain length and that the stabilisation effect on the PS is due to an inhibiting action of dipentene evolved by the PI. Both these reactions follow diffusion of mobile species of rather low volatility from the PI phase into the PS phase.     

Crystallization behavior and morphology of one-step reaction compatibilized microfibrillar reinforced isotactic polypropylene/poly(ethylene terephthalate) (<Emphasis Type="Italic">i</Emphasis>PP/PET) blends

One-step reaction compatibilized microfibrillar reinforced iPP/PET blends(CMRB) were successfully prepared through a "slit extrusion-hot stretching-quenching" process.Crystallization behavior and morphology of CMRB were systematically investigated.Scanning electronic microscopy(SEM) observations showed blurry interface of compatibilized common blend(CCB).The crystallization behavior of neat iPP,CCB,microfibrillar reinforced iPP/PET blend(MRB) and CMRB was investigated by differential scanning calorimetry(DSC) and polarized optical microscopy(POM).The increase of crystallization temperature and crystallization rate during nonisothermal crystallization process indicated both PET particles and microfibrils could serve as nucleating agents and PET microfibrils exhibited higher heterogeneous nucleation ability,which were also vividly revealed by results of POM.Compared with MRB sample,CMRB sample has lower crystallization temperature due to existence of PET microfibrils with smaller aspect ratio and wider distribution.In addition, since in situ compatibilizer tends to stay in the interphase,it could also hinder the diffusion of iPP molecules to the surface of PET phase,leading to decrease of crystallization rate.Two-dimensional wide-angle X-ray diffraction(2D-WAXD) was preformed to characterize the crystalline structure of the samples by injection molding,and it was found that well-developed PET microfibrils contained in MRB sample promoted formation ofβ-phase of iPP.     

Thermomechanical study of low-density polyethylene, polyamide 6 and its blends

By using thermomechanical analysis (TMA) multiple relaxation transitions in the amorphous part of semi-crystalline polymers and their blends can be found. These result from differences in the interaction energies between segments of macromolecules, and as a result, in molecular mobility. TMA shows essential changes in the structure of low-density polyethylene (LDPE) resulting from the grafting of a maleic anhydride (LDPE-g-MAH) onto this semi-crystalline polymer. The grafting process did not suppress the ability of polyethylene to crystallize. Essential changes were found in molecular weight distribution and relaxation transitions of the ternary blends LDPE/PA6 (polyamide 6, PA6)/LDPE-g-MAH studied. For a concentration of PA6 up to 30 wt.%, a single relaxation transition is visible, which testifies that the components are miscible in the amorphous region. For blends with 40 and 50 wt.% of PA6, this structure was transformed and two relaxation transitions are visible. From the results obtained in this study it is concluded that the introduction 5 wt.% of grafted polyethylene is sufficient to produce a PA6/LDPE blend only for PA6 concentration up to 30 wt.% which is homogenous on “molecular” level. The transformation of the structure of the ternary polymer blend was explained by the interaction of the components during the melt mixing and changes in the structure of its amorphous regions.     

等规聚丙烯/二元乙丙橡胶合金相分离对结晶动力学的影响

用小角激光光散射(SALLS)、相差显微镜(PCM)、示差扫描量热仪(DSC)和偏光显微镜(POM)研究了聚丙烯/二元乙丙橡胶(iPP/EPR)共混体系的相分离行为和等温结晶行为.发现iPP/EPR(50/50,W/W)发生的液-液相分离遵循spinodal机理.通过Cahn-Hilliard方程求得了不同实验温度下iPP/EPR的表观扩散系数(Dapp)以及spinodal温度(Ts).考察了不同相分离程度的iPP/EPR体系结晶动力学,发现延长相分离时间(tps)或提高相分离温度(Tps)均会导致半结晶时间(t1/2)增大,即结晶速率降低.这被归于EPR成核作用的降低.动力学分析结果表明Avrami模型适用于描述该体系的等温结晶过程,其结晶机理基本不受相分离程度的影响,结晶均以瞬时成核和三维生长为主.     

iPS－b－iPP共聚物对iPS／iPP共混物的性能和形态影响的研究

报道了苯乙烯－丙烯等规嵌段共聚物（ｉＰＳ－ｂ－ｉＰＰ）增溶作用及ｉＰＳ－ｂ－ｉＰＰ／ｉＰＳ／ｉＰＰ三组分共混体系微观形态和力学性能的研究结果。ｉＰＳ－ｂ－ｉＰＰ的加入明显地改善了ｉＰＳ／ｉＰＰ二组分共混物的力学性能;共聚物含量超过１５％时,三组分共混物的抗冲击强度超过ＮＩＰＳ的抗冲击强度,并具有较高的耐热性。ＳＥＭ结果表明,ｉＰＳ－ｂ－ｉＰＰ在ｉＰＳ／ｉＰＰ共混中起到了相分散和相间“偶联”作用,并降低了共混体系的微相尺寸和增加相间相互作用或粘附性。ｉＰＳ－ｂ－ｉＰＰ／ｉＰＳ／ｉＰＰ共混合金具有高的软化温度和刚性。     

Semicrystalline blends of polyethylene and isotactic polypropylene: Improving mechanical performance by enhancing the interfacial structure

The low‐temperature mechanical behavior of semicrystalline polymer blends is investigated. Isotactic polypropylene (iPP) is blended with both Zeigler–Natta polyethylene (PE) and metallocene PE. Transmission electron microscopy (TEM) on failed tensile bars reveals that the predominate failure mode in the Zeigler–Natta blend is interfacial, while that in the metallocene blend is failure of the iPP matrix. The observed change in failure mode is accompanied by a 40% increase in both tensile toughness and elongation at −10 °C. We argue that crystallite anchoring of interfacially entangled chains is responsible for this dramatic property improvement in the metallocene blend. The interfacial width between PE and iPP melts is approximately 40 Å, allowing significant interfacial entanglement in both blends. TEM micrographs illustrate that the segregation of low molecular weight amorphous material in the Zeigler–Natta blend reduces the number and quality of crystallite anchors as compared with the metallocene blend. The contribution of anchored interfacial structure was further explored by introducing a block copolymer at the PE/iPP interface in the metallocene blend. Small‐angle X‐ray scattering (SAXS) experiments show the block copolymer dilutes the number of crystalline anchors, decoupling the interface. Increasing the interfacial coverage of the block copolymer reduces the number of anchored interfacial chains. At 2% block copolymer loading, the low‐temperature failure mode of the metallocene blend changes from iPP failure to interfacial failure, reducing the blend toughness and elongation to that of the Zeigler–Natta blend. This work demonstrates that anchored interfacial entanglements are a critical factor in designing semicrystalline blends with improved low‐temperature properties. © 2000 John Wiley & Sons, Inc. J Polym Sci B: Polym Phys 38: 108–121, 2000     

Degradation of polymer blends—II. Oxidative radiolysis and stabilization of blends of low-density polyethylene and styrene-butadiene-styrene copolymers

The solubility, infra-red and mechanical properties have been studied for LDPE-SBS blends irradiated with γ-rays in the presence of oxygen. The results have been compared with those obtained for the oxidative radiolysis of pure LDPE and for the photo-oxidation of the same LDPE-SBS blend. The oxidative degradation mainly occurs in the polybutadiene part of the blend. Efficient stabilization by hindered amines Tinuvin 770 is reported.