纳米CaCO3改性聚合物基复合材料研究进展

纳米碳酸钙是一种原料丰富、性能优良的无机填料,在聚合物填充改性方面,纳米碳酸钙填充聚合物基复合材料具有一些普通填充体系无法达到的优良性能。本文综述了纳米碳酸钙在聚甲基丙烯酸甲酯、聚氯乙烯和聚丙烯等材料中的改性研究进展,并对纳米填充粒子和聚合物基体的相容性及增强增韧机理进行了讨论。     

Gas absorption with filled polymer systems

This paper deals with the gas absorption behavior of polymer systems. The emphasis is on the difference between filled and unfilled polymers to explain heterogeneous nucleation in filled polymers. A Foaming Process Simulator has been built to study the gas absorption. It consists of a test chamber that holds the polymer samples. The chamber can be pressurized with gas up to 5000 psi and heated up to 450°F. The gas pressure is monitored by a high‐accuracy pressure transducer and recorded by a data acquisition system. The amount of gas absorbed by a polymer is determined from the pressure change in the test chamber. A rotor applies shear to the polymer melt to investigate the shear effects. Two polymer systems were tested: HDPE with/without talc, and PVC with/without calcium carbonate. The fillers were well dispersed as verified with scanning electron microscope. The tests were done at the melt temperatures from 120°C to 177°C and a saturation pressure of about 18.9 MPa. It was found that the filled polymers absorb more gas compared to the unfilled ones. It is suggested that there is a certain amount of gas accumulated in the filler‐polymer interface. This accumulated gas helps to create cells during the foaming process.     

State of dispersion: Polypropylene filled with calcium carbonate

The influence of mixing conditions on the state of dispersion of calcium carbonate filled polypropylene composite was studied. The polymer and the filler were compounded in a twin screw extruder under various controlled processing conditions. The variables studied were the screw speed, the feed rate, the filler concentration, the barrel temperature profile and the surface treatment of the filler. The state of dispersion of calcium carbonate filled polypropylene composites was characterized using a scanning electron microscope, and was correlated to the residence time and the shearing conditions that were prevailing within the extruder. Degradation of the polymer matrix was also observed.     

Weathering of polypropylene composites containing weldlines

Abstract

This work deals with the weathering behaviour of polypropylene composites containing fillers with various aspect ratios (glass fibre, talc, and calcium carbonate). Single and double end gated injection moulded bars were exposed outdoors in Campina Grande (Brazil) for periods up to 45 weeks and then characterised using infrared spectroscopy, tensile testing, and surface fractography. The unfilled polymer displayed the highest level of mechanical deterioration, followed by polypropylene containing glass fibre, whereas compounds with talc and calcium carbonate were the most resistant to photodegradation. These results are partially a consequence of the screening effect caused by talc and calcium carbonate at the exposed surface. The results indicated that weldlines make the parts weaker, although the strength loss caused by weathering of double end gated samples was similar to that observed with mouldings produced by single gated injection. It was also observed that the adhesion between glass fibre and the polymer matrix was much reduced after weathering, probably as a result of diffusion of water to the interface.     

Influence of chalk and its surface treatment on crystallization of filled polypropylene

Isotactic polypropylene has been shown to crystallize from the melt spherulitically at intermediate undercoolings (100–130°C) in the presence of a high amount (40 wt %) of chalk (calcium carbonate). Linear growth rate is not remarkably affected by the presence of a filler. Both nonisothermal and isothermal crystallization DSC experiments indicate that chalk acts as a weak nucleant. Introduction of liquid [oligomer of ethylene oxide (OEO), M_w = 300] at polymer–filler interface lowers the nucleating activity of chalk. Analysis of crystallization kinetics in Avrami coordinates, followed by dimensional-analysis correction for the case of nonintegral values of exponents, indicates that the amount of extra “chalk nuclei” is approximately constant in the range of 100–130°C while the amount of OEO-modified “chalk nuclei” decreases with the increase of the crystallization temperature. Comparison of the melting endotherms indicates that filled melt-crystallized material contains higher fraction of lower melting crystallites than unfilled polypropylene. This fraction is also higher in the case of polypropylene filled with unmodified chalk. Nucleating activity of chalk has been shown to depend upon its crystal structure (calcite or aragonite), surface topography, and aggregation.     

Advances in the use of molybdenum compounds as smoke suppressants for PVC

Molybdenum-based compounds are effective smoke suppressants for rigid and flexible polyvinyl chloride formulations, both unfilled and filled with calcium carbonate and alumina trihydrate. These compounds, two of which are new compounds based on zinc molybdate with or without a phosphite synergist, are useful as is or extended onto core materials such as clay or talc. The addition of molybdenum-containing additives to flexible PVCs containing antimony trioxide usually raises the oxygen index and thus improves flame retardancy. Tests indicate that molybdenum acts as a flame and smoke suppressant in the solid phase.     

The role of filler type in the photo‐oxidation behaviour of micro‐ and nano‐filled polypropylene

The rising interest in polymer nanocomposites leads also to an increasing concern for their photo‐oxidation resistance. The main properties and photo‐oxidation behaviour of polypropylene‐based microcomposites and nanocomposites were investigated. The results show that the use of nanosized calcium carbonate may lead to a higher photo‐oxidation rate than that of pristine polypropylene, in a way that is comparable to organo‐modified nanoclays. It is also observed that nanosized calcium carbonate causes higher photodegradation rates than microsized calcium carbonate. The main reasons for the increased photo‐oxidation rates when using organo‐modified nanoclays include the presence of iron ions, the degradation of the organo‐modifier and the formation of acidic sites on nanoclay layers, while in the case of calcium carbonate the main reasons are related to the achieved morphology and structure. The presence of calcium carbonate, especially when nanosized, significantly modifies the distribution of photo‐oxidation products in comparison to clay‐filled nanocomposites. Copyright © 2011 Society of Chemical Industry     

Co-injection molding of reinforced polymers

Co-injection molding of calcium carbonate filled polypropylene, short glass-fiber-filled polypropylene, or unfilled high-density polythylene melts is studied using a mediumsize injection-molding machine and a center-gated disc mold. Injection molding is carried out under non-isothermal conditions. Order of injection of the melts, injection speed, and mold temperature is changed in order to understand the mold filling in general and to investigate the type of skin/core structure and mechanical interlocking of the phases in the moldings. It is found that the order of injection is not significant in obtaining a skin/core structure but it is important in obtaining extensive phase interlocking, which is reduced if the flow rafe and the mold temperature are low. Presence of fillers appears to result in more mechanical interlocking of the phases.     

Non-isothermal crystallization kinetics of calcium carbonate-filled β-crystalline phase polypropylene composites

The non-isothermal crystallization behaviour of high purity β-phase and α-phase polypropylene (PP) and their calcium carbonate-filled composites was investigated by means of differential scanning calorimetry. High purity β-PP polymer was prepared by adding an effective β-nucleator consisting of equal amounts of pimelic acid and calcium stearate. The crystallization temperature and crystallization rate coefficient of pure β-PP polymer were considerably higher than those of the α-PP polymer. This was due to the β-PP polymer containing nucleating agents, which act as nuclei for β-spherulites. The calcium carbonate content had little or no effect on the crystallization rate coefficient and Ozawa exponent of the β-phase PP in the composites. On the other hand, the crystallization temperature, crystallization rate coefficient and Ozawa exponent of the α-phase PP composites depended on the calcium carbonate loading. The effect of calcium carbonate additions on the crystallization of α-PP and β-PP is discussed. ©1997 SCI     

An investigation on the mechanical and dynamic rheological properties of single and hybrid filler/polypropylene composites based on talc and calcium carbonate

Some results of experiments on the mechanical and rheological properties of mineral filled polypropylene were presented. Single filler and hybrid filler composites of talc and calcium carbonate (CaCO₃) were prepared in a co‐rotating twin‐screw extruder. The effect of filler type, filler content, and coupling agent on the mechanical and rheological properties of the polypropylene were studied. The coupling agent was maleic anhydride‐grafted polypropylene (PP‐g‐MA). It was found that the mechanical properties are affected by filler type, filler concentration, and the interaction between filler and matrix. The tensile strength of the composite is more affected by the talc while the impact strength is influenced mostly by CaCO₃ content. The elongation at break of PP/CaCO₃ composites was higher than that of PP/talc composites. The incorporation of coupling agent into PP/mineral filler composites increased the mechanical properties. Rheological properties indicated that the complex viscosity and storage modulus of talc filled samples were higher than those of calcium carbonate filled samples while the tan δ was lower. The rheological properties of hybrid‐filler filled sample were more affected by the talc than calcium carbonate. The PP‐g‐MA increased the complex viscosity and storage modulus of both single and hybrid composites. POLYM. COMPOS., 2009. © 2009 Society of Plastics Engineers     

A novel method to prepare zinc hydroxystannate-coated inorganic fillers and its effect on the fire properties of PVC cable materials

Fire-retardant (FR) properties, including limiting oxygen index, peak rate of heat release, and smoke parameter have been measured and compared for unfilled and filled polyvinyl-chloride (PVC)-based cable formulations, containing 15 wt% amounts of uncoated and zinc-hydroxystannate (ZHS)-coated magnesium hydroxide (MH) and calcium carbonate (CaCO₃) fillers at the same addition level. Of the uncoated fillers, MH was more effective at lowering flammability than CaCO₃. When the ZHS coating was applied to MH and CaCO₃, CaCO₃ became the most effective additive at lowering PVC flammability and smoke output. POLYM. ENG. SCI., 47:1163–1169, 2007. © 2007 Society of Plastics Engineers     

Single screw extrusion compounding of particulate filled thermoplastics: State of dispersion and its influence on impact properties

The compounding of calcium carbonate filled polypropylene (PP) is discussed with reference to a single-screw extruder and variants of mixing sections. The mixing section on the screw is exchangeable, and two dispersive mixing elements, namely the Zorro and the Maddock elements, were used. The calcium carbonate was surface treated with a liquid titanate coupling agent (LICA12). The impact strength was measured by a notched Izod impact tester with specimens having a U-shaped sharp notch. The fracture toughness for the PP homopolymer and the filled composites was determined using fracture mechanics principles. The results were correlated with the state of dispersion of the calcium carbonate filler. The effects of filler concentration and surface treatment were examined as well. Correlation between state of dispersion and impact properties for calcium carbonate filled PP was obtained. We also investigated the effect of various mixing elements on the state of dispersion. The experimental results indicate that good dispersion would improve the impact properties of the polymer matrix, but only at moderate filler loading. © 1996 John Wiley & Sons, Inc.     

晶须状碳酸钙填充聚合物材料性能的研究

研究了晶须状碳酸钙的填充量及表面处理状况对填充ＰＶＣ材料和ＰＰ材料性能的影响。力学性能和流变性能的测试结果表明，碳酸钙晶须作为填充材料，在相同的填充量下加工 交小、拉伸强度和冲击强度较高，对晶须进行适当的表面处理后，体系的性能可以得到进一步提高，这是因为晶须具有特殊的针状外形，在加工应力的作用下可以迅速地在聚合物熔体中定向排列，对体系起到良好的增强和增韧作用。     

Tensile property and interfacial dewetting in the calcite filled HDPE, LDPE, and LLDPE composites

Mechanical properties and complex melt viscosity of unfilled and the calcite (calcium carbonate: CaCO₃) filled high density polyethylene (HDPE), low density polyethylene (LDPE), and linear low density polyethylene (LLDPE) composites using dumbbell bar and film specimens are studied. In addition, the formation of air holes between calcium carbonate and the resin matrix was investigated from the phase morphology and interfacial behavior between the above constituents upon stretching using scanning electron microscopy. The tensile stress and the complex melt viscosity of the calcite filled (50%) polyethylene composites were higher than that of unfilled ones, implying that the reinforcing effect of calcium carbonate. The crack was initiated up to first 50% elongation along the transverse direction and the formation of air holes was originated by dewetting occurring through machine direction in the interface between calcium carbonate surface and HDPE. The propagation mechanism of the air hole formation was proposed to firstly originate by dewetting up to 300% elongation, and enlarged not only by breaking of a superimposed fibril structure, but also by merging effect air holes between fibrous resin matrix. However, the crack propagation was not observed at the very beginning elongation for the calcite filled LDPE and LLDPE systems. Less fibril structure was observed in LLDPE, then LDPE composites. The observed shape and the average size of the air holes were different from system to system. This sort of different interfacial behavior and mechanical properties may arise from different configuration of polyethylene.     

Photodegradation of talc-filled polypropylene

Injection-molded talc-filled polypropylene (PP) composites have been exposed to ultraviolet (UV) radiation in the laboratory for periods up to 26 weeks. The extent of chemical degradation has been assessed by means of Fourier transform infrared spectroscopy (FTIR) and gel permeation chromatography (GPC), and the results correlated with the mechanical properties. In the early stages of exposure, the photo-oxidation is faster in the talc-filled composites than in the unfilled polymer, but this trend is reversed for exposures longer than ∼12 weeks. Scanning electron microscopy (SEM) inspection has revealed that surface cracks caused by photodegradation in the filled PP occur in the surface exposed to the UV source only, resulting in much less deterioration in tensile properties when compared with the unfilled polymer which degrades significantly at the unexposed surface also. Measurements of melting temperatures by differential scanning calorimetry (DSC) gave a consistent picture of degradation with that obtained by FTIR and GPC studies. DSC analyses have also shown that an increase in the melting enthalpy for both the unfilled and filled grades occurs during exposure.     

Fracture behavior of glass bead-filled poly(oxymethylene) injection moldings

The mechanical properties of glass bead filled poly(oxymethylene) were investigated as a function of glass bead content and glass bead diameter using injection molded test pieces. Fracture toughness measurements were made using single edge-notched tension and single edge-notched bend specimens. The effect of notch orientation with respect to the mold fill direction on fracture toughness was studied using single gate and double gate moldings. Tensile strength and flexural modulus were measured using standard test pieces. It was found that; (i) fracture toughness of the filled and unfilled polymer was relatively independent of notch orientation, (ii) the presence of weldlines in the molded test pieces did not affect the fracture toughness of unfilled polymer or its composites, (iii) fracture toughness of filled polymer was always considerably lower than that of the unfilled polymer; fracture toughness decreased sharply with increasing bead concentration, (iv) fracture toughness was not a sensitive function of glass bead diameter; it decreased slightly as bead diameter increased, (v) strain energy release rate as measured under impact decreased with increasing bead concentration, (vi) tensile strength decreased linearly with increasing glass bead concentration and was inversely proportional to the square root of the bead diameter, (vii) weldlines did not affect the tensile strength of the polymer or its composities, (viii) flexural modulus increased linearly with increasing glass bead concentration according to the Einstein equation.     

Flame retardation of polypropylene: Effect of silane treated antimony compounds

Flame retardation of polypropylene was accomplished by blending with antimony compounds (Sb₂O₃ and SbPO₄) in conjunction with polyvinyl chloride (PVC) or ferric oxide. The compatibility and dispersion of antimony compounds in the polymer matrix was enhanced by using silane coupling agents, viz., vinyltriethoxysilane (A-151) and γ-aminopropyltriethoxysilane (A-1100). Rheological properties of filled polypropylene were studied in the temperature range 180 to 220°C at shear rates of 29.5 to 119.5 sec^?1. An increase in the melt viscosity was found in the filled polypropylene as compared to virgin polymer. Silanation of antimony compounds also influenced the melt rheology of flame retardant polypropylene. Incorporation of 6 phr Sb₂O₃ and 19 phr PVC raised the oxygen index of polypropylene to 22.9 and this sample was found to be self extinguishing in 65 s with a burning rate of 0.06 mm/s as compared to 1.1 mm/s for unfilled polypropylene. Though silanation of antimony compounds slightly reduced the oxygen index of flame retardant polypropylene, yield strain and flexural rigidity of injection molded samples was improved over unsilanated flame retardant polymer.     

Shear yield behavior of calcium carbonate–filled polypropylene

The rheological properties of calcium carbonate-filled polypropylene has been examined using a Rheometrics dynamic analyzer RDAII. The study included a steady shear test, a transient stress growth test, and a dynamic oscillatory shear flow. Yield behavior was observed in all kinds of rheological tests for highly filled compounds when the volume loading exceeded a critical value at about 20%. The empirical Cox-Merz rule, which is usually applicable to an unfilled polymer, was found to be invalid for highly filled compounds. The modified Cox-Merz rule, in which the apparent viscosity versus the shear rate is equal to the complex viscosity versus the frequency-amplitude in the nonlinear region, was found to be valid only for highly filled compounds. The viscosity and the apparent yield values appear to increase with increasing volume loading of filler particles. The surface treatment of fillers, which presumably reduces the interaction between filler particles and the extent of agglomeration, results in major viscosity reductions and decreases in apparent yield values. The yield values determined from various tests are not the same. The results are interpreted in terms of a system forming a filler network due to weak inter-particle forces. The yield stress resulting from the breakdown and recovery of the network is thus dependent on the characteristic time of the individual test.     

超细重质碳酸钙填充聚丙烯的研究

利用双螺杆挤出机制备了超细重质CaCO3填充聚丙烯(PP)复合材料。测得了PP/超细重质CaCO3复合材料的力学性能。采用SEM、XRD、DSC对PP/超细重质CaCO3复合材料进行了研究。结果表明:超细重质碳酸钙在基体中基本实现了良好分散;在一定填充范围内,超细重质CaCO3的加入可以极大的提高复合材料的冲击强度;复合材料的结晶度随超细重质碳酸钙填充量的增加而有所降低,但复合材料的熔点变化不大。     

Different β nucleants and the resultant microstructural,fracture, and tensile properties for filled and unfilled ISO polypropylene

This article explores the use of two β nucleants to improve the fracture behavior of filled and unfilled homo‐polypropylene (PP). The first was based upon an organic quinacridone, whereas the second was based upon the inorganic calcium pimelate. Formulations containing various concentrations of nucleant were prepared using single screw extrusion and then characterized by X‐ray diffraction, differential scanning calorimetry (DSC), Izod impact strength, and tensile testing. The quinacridone nucleating agent produced higher levels of β crystallinity and better improvement in strain to failure, whereas the calcium pimelate imparted greater improvement in impact strength regardless of whether the PP was filled or unfilled. No direct relationship between β crystallinity and fracture properties was observed though synergistic enhancement in impact strength was evident. By varying the concentration of calcium carbonate in the calcium pimelate from 10 : 1, 5 : 1, 2 : 1, and 1 : 1 weight composition of calcium carbonate to pimelic acid, similar property enhancements were achieved regardless of composition although the 10 : 1 sample did produce superior elongation to break. The importance of cooling rate on microstructure within each sample was explored via a through the thickness study using DSC and nano‐indenting methods. Variations in the β content through the thickness were related to cooling and found to be independent of sample composition and processing. Elastic properties varied inversely with β content. © 2012 Wiley Periodicals, Inc. J. Appl. Polym. Sci., 2013