Polypropylene/calcium carbonate nanocomposites

Polypropylene (PP) and calcium carbonate nanocomposites were prepared by melt mixing in a Haake mixer. The average primary particle size of the CaCO₃ nanoparticles was measured to be about 44 nm. The dispersion of the CaCO₃ nanoparticles in PP was good for filler content below 9.2 vol%. Differential scanning calorimetry (DSC) results indicated that the CaCO₃ nanoparticles are a very effective nucleating agent for PP. Tensile tests showed that the modulus of the nanocomposites increased by approximately 85%, while the ultimate stress and strain, as well as yield stress and strain were not much affected by the presence of CaCO₃ nanoparticles. The results of the tensile test can be explained by the presence of the two-counter balancing forces—the reinforcing effect of the CaCO₃ nanoparticles and the decrease in spherulite size of the PP. Izod impact tests suggested that the incorporation of CaCO₃ nanoparticles in PP has significantly increased its impact strength by approximately 300%. J-integral tests showed a dramatic 500% increase in the notched fracture toughness. Micrographs of scanning electron microscopy revealed the absence of spherulitic structure for the PP matrix. In addition, DSC results indicated the presence of a small amount of β phase PP after the addition of the calcium carbonate nanoparticles. We believe that the large number of CaCO₃ nanoparticles can act as stress concentration sites, which can promote cavitation at the particle-polymer boundaries during loading. The cavitation can release the plastic constraints and trigger mass plastic deformation of the matrix, leading to much improved fracture toughness.     

The toughening mechanism of polypropylene/calcium carbonate nanocomposites

The toughening mechanism of polypropylene (PP) filled with calcium carbonate (CaCO₃) nanoparticles is described. In a previous study (Macromolecule 2008;41:9204), we observed that intensive ligament-stretching following debonding of nanoparticles was responsible for the significant improvement in the impact toughness of the annealed PP/CaCO₃ nanocomposites. Furthermore, we hypothesized that strong ligaments, which have high fracture stresses, are needed to stabilize the crack-initiation process and to increase the energy dissipation in the crack-initiation stage. In this study, we used a high-molecular-weight PP to test this hypothesis because strong ligaments could be created from this high-molecular-weight PP. The notched Izod impact strength of the nanocomposites containing the high-molecular-weight PP and 20 wt% CaCO₃ nanoparticles with a monolayer coating of stearic acid was measured to be about 370 J/m, whereas the impact strength of the unfilled PP was 50 J/m. The size of the plastic deformation zone was found to be dependent on the molecular weight of the PP matrix because the strong ligaments of the high-molecular-weight PP enabled the expansion of the plastic deformation zone, leading to a considerable increase in the impact strength. The synergic effect of the high-molecular-weight PP and the monolayer-coated nanoparticles produced nanocomposites with high impact strength, which is much greater than the inherent impact strength of the unfilled polymer. In addition, the effect of the high-molecular-weight PP on the dispersion of the nanoparticles was investigated.     

Solvothermal preparation of maleic anhydride grafted onto acrylonitrile-butadiene-styrene terpolymer (ABS)

The grafting copolymerization of maleic anhydride (MAH) onto acrylonitrile-butadiene-styrene terpolymer (ABS) was carried out through solvothermal process. Infrared (IR) spectra and ¹H NMR spectra confirmed that maleic anhydride was successfully grafted onto the ABS backbone. The influences, such as MAH concentration, the initiator's content, reaction temperature and time, comonomer, ABS concentration and different solvents, on the grafting copolymerization were also studied. Results indicated that the preparation of MAH grafted onto ABS through solvothermal method can be carried out in both good solvent and poor solvent, which is much different from the traditional solution grafting method, and high grafting degree can be obtained in good solvent.     

一种针状纳米碳酸钙的制备方法

用石灰乳液碳酸化法制备出针状纳米碳酸钙微粒,讨论了碳化温度和结晶导向剂用量等因素对纳米碳酸钙粒径和形貌的影响。结果表明:结晶导向剂用量为1%~3%(质量分数),温度为14℃,氢氧化钙浆液浓度为8%~12%(氢氧化钙占浆液的质量分数),CO2气体浓度为40%~60%(体积分数),搅拌速度为200~300 r/m in时能制备出长径比大、粒径分布均匀、分散性好的产品;并采用TEM,XRD对其结构进行了表征。     

纳米碳酸钙的原位包覆及应用

为更好地改性纳米碳酸钙,采用脂肪酸（SA）对纳米碳酸钙进行原位包覆,并对原位包覆法机理作了探讨。先在纳米碳酸钙浆液中加入一定量强碱,然后将浆液加热至75.0～90.0 ℃,再在机械搅拌辅助下加入适量脂肪酸,浆液经过滤、干燥和粉碎解聚得表面包覆改性的纳米碳酸钙。包覆碳酸钙的吸油值、接触角测试,扫描电子显微镜表征及其在室温硫化硅橡胶和DOP糊中的应用实验表明：脂肪酸在纳米碳酸钙表面形成均匀、完整的包覆层,改性碳酸钙在聚合物中具有极佳的应用效果。研究发现,温度为90 ℃,n（SA+OA）∶n（OH^-）=1∶1,n（SA+OA）/m（CaCO₃）= 1.0×10^-4 mol/g是原位法表面包覆纳米碳酸钙比较合适的条件。     

彩色纳米碳酸钙的研制

以纳米碳酸钙中试装置为平台,通过控温碳化、加热湿法染色、加热湿法改性和分散处理,制得了具有良好一次粒子形态的彩色纳米碳酸钙产品。激光粒度仪测试表明,彩色纳米碳酸钙产品的D₅₀约为350 nm,具有粒度分布均匀、分布范围窄等特点。产品在空气中长期放置不氧化、不褪色,说明具有良好的化学稳定性。亲水性实验表明,彩色纳米碳酸钙产品在水中长时间放置、反复搅拌,仍然不沉降、不掉色,说明染色和活化都是牢固的。以酸性媒染蓝黑B染料和硬酯酸为例,分析了纳米碳酸钙的湿法染色和湿法活化机理,并且探讨了硬酯酸分子、染色剂分子和碳酸钙颗粒之间的化学交联作用。     

超声辅助制备针状纳米活性碳酸钙的研究*

针状碳酸钙是一种质优价廉的新型无机填料,可广泛应用于塑料、橡胶、造纸等领域。以简化实验方法和节省能源为目的,采用超声辅助并选用合适的改性剂,合成和改性一体化进行了制备针状纳米活性碳酸钙的实验。综合考察了溶液浓度、改性剂用量、反应温度、加水量等反应条件,通过正交实验得到最佳反应条件：溶液浓度为0.05 mol/L、反应温度为60 ℃,改性剂用量为1.25%（质量分数）、加水量为60 mL、超声功率为250 W、搅拌速度为200 r/min。经过验证实验,最终制得平均粒径为150 nm、长径比为21.7、活化度为98.67%、吸油值为0.455 g/g的针状纳米活性碳酸钙。     

碳酸钙在复合改性中的应用

无机填料碳酸钙在聚丙烯复合体系中的应用,研究了碳酸钙的加入对聚丙烯光学性能、分散性、力学性能中的冲击强度的影响,同时深入分析了无机填料对聚丙烯复合体系的增强增韧机理。     

纳米碳酸钙悬浮体流变性能研究

以碳酸钙、氧化钙和邻苯二甲酸二辛酯组成的悬浮体为研究对象,模拟了碳酸钙在涂料及密封胶中流变行为,探讨了碳酸钙颗粒形貌、粒径及表面状态对其流变性能的影响。结果表明：不同形貌碳酸钙制备的悬浮体分散稳定性从强到弱依次为：立方形、纺锤形、链状。立方形碳酸钙配制成的悬浮体触变性最好,屈服应力最大;纳米碳酸钙平均粒径越大,粒径分布区间越窄,颗粒规整程度越高,其悬浮体触变性及屈服应力也越高。随着包覆量增加,触变性增强,但包覆量超过3%（质量分数）时,呈现出负触变性。     

Synthesis of nanosized calcium carbonate (aragonite) via a polyacrylamide inducing process

A carbonation route for the synthesis of nanosized calcium carbonate (aragonite) was studied. In the process, polyacrylamide was used as an organic substrate to induce the nucleation and growth of calcium carbonate. The calcium carbonate particles were produced by means of carbonation of the mixture of calcium hydroxide and polyacrylamide by bubbling CO₂/N₂ gas mixture_. The operating parameters such as the concentration of organic substrate and temperature were varied to study their influences on the polymorph and crystal sizes of calcium carbonate particles. The morphology of the calcium carbonate particles was characterized with transmission electron micrograph (TEM). The synthesized calcium carbonate particles in the presence of organic substrate are the mixture of aragonite with needle shape and calcite with cubic shape. Fourier transform infrared spectroscopy (FTIR) analysis reveals the presence of aragonite and calcite. The polymorphs and their crystal sizes were characterized with X-ray diffraction (XRD). The calcium carbonate nucleated in the organic substrate exhibited different endothermic peak in differential thermal gravity (DTG) results compared to one coexisting with the organic substrate.     

添加剂对纳米碳酸钙形貌与粒度的影响

采用碳化法和复分解法,通过选用不同添加剂及控制其添加量制备了不同形貌和粒径的纳米碳酸钙。用TEM、SEM对所得产物的形貌和尺寸进行了表征。结果表明,当柠檬酸的添加量为0.25%~0.75%（质量分数,下同）时,可实现对纳米碳酸钙颗粒粒径的调控,并选用硬脂酸钠作为表面改性剂对其进行改性,改性后的纳米碳酸钙颗粒更大,形状更规整,分散性更好;当季戊四醇添加量为0.1%~10%时,分别制备出了不同粒径的球形和立方形纳米碳酸钙颗粒。初步探讨了有机酸类、糖类和醇类对合成纳米碳酸钙的影响效果和作用机理。     

Synthesis of exfoliated acrylonitrile-butadiene-styrene copolymer (ABS) clay nanocomposites: role of clay as a colloidal stabilizer

Acrylonitrile-butadiene-styrene copolymer (ABS) clay nanocomposites were synthesized using two clays (sodium montmorillonite, laponite). Both colloidal stability and mechanical properties of the nanocomposites were dependant on aspect ratios of clays. Laponite, a low aspect ratio clay, reduced particle sizes of ABS clay nanocomposite latexes, enhanced colloidal stabilities, and increased viscosity of the latexes. The colloidal stability of ABS clay latexes may result from four factors. Firstly, the electrostatic repulsion forces originated from surface charges of clays and anionic surfactant contribute to colloidal stability. Secondly, laponite layers separate sodium montmorillonite layers and polybudadiene latex particles preventing the coagulation. Thirdly, the laponite layers adsorbed on latexes act like steric barriers against coagulation. Fourthly, increased viscosity reduces latex mobility, lowering collision possibility among latex particles. Resultant ABS clay nanocomposites showed exfoliated structures, and their mechanical properties related to the relative weight ratio of sodium montmorillonite to laponite: as portions of sodium montmorillonite increased, dynamic moduli of the nanocomposites increased, because sodium montmorillonite has higher aspect (length/thickness) ratio than laponite.     

Comparison of polylactide/nano-sized calcium carbonate and polylactide/montmorillonite composites: Reinforcing effects and toughening mechanisms

Semicrystalline polylactide (PLA) exhibits high tensile strength and modulus but very low strain-at-break and toughness. In this study, PLA nanocomposites with nano-sized precipitated calcium carbonate (NPCC) and organically modified montmorillonite (MMT) clay were prepared by melt extrusion. Morphologies, tensile mechanical properties, dynamic mechanical and rheological properties, polymer–nanoparticle interactions, and toughening mechanisms of the PLA/NPCC and PLA/MMT nanocomposites were compared. MMT and NPCC showed significantly different effects on the strength, modulus and elongation of the PLA nanocomposites. Different toughening mechanisms were first elucidated for the two types of nanocomposites based on the evidence from both macroscopic and microscopic observations. Under uniaxial tension, large quantities of microvoids were created in both PLA nanocomposites. The microvoids in PLA/NPCC caused massive crazing, while in PLA/MMT they resulted in shear yielding, particularly in the nanocomposite with 2.5 wt% MMT. The MMT stacks and platelets were found to be located between the microvoids in the extended specimens and prevented them from collapsing and coalescing.     

镍、锌盐对纳米碳酸钙结晶的影响

采用复分解法,设计了适当的反应装置和实验条件,分别以硝酸镍、硫酸锌作晶型控制剂,合成了纳米碳酸钙。使用傅里叶变换红外拉曼光谱仪、扫描电子显微镜、X射线衍射分析仪对产物进行表征。结果表明,硝酸镍、硫酸锌的加入对碳酸钙的结晶有比较明显的影响,出现了多种不同形态的颗粒,产品呈现出方解石型、球霰石型、文石型的微晶。该研究为不同添加剂的使用及效果提供了实验数据,为此类反应提供了可行的实验经验和思路。     

碳酸钙干燥设备概况与发展

对碳酸钙（轻钙，重钙，纳米钙，专用钙等）的干燥及其有关设备的现状和发展作了回顾，并就轻钙、重钙、纳米钙等干燥效率的提高、设备的改进以及组合干燥的应用实际效果作了阐述。     

Preparation of ABS/montmorillonite nanocomposite using a solvent/non-solvent method

Polymer layered silicate nanocomposites have been studied for many years and due to their distinguished properties and applications, it is still the subject of many research programs. There are different methods of preparation, with the melt intercalation method as the mostly used method. Due to the thermal destructive effects of melt mixing on the polymer chains there are currently efforts to develop some new methods of preparation. A solvent/non-solvent method has been developed in this study for the preparation of ABS/clay nanocomposites. ABS nanocomposite is precipitated after addition of ethanol (non-solvent) containing organic modified montmorillonite from a THF solution while it is stirring. A kind of mixing system known as homogenizer has been used in this work. The final product has been determined having an intercalated structure with a uniform interlayer spacing of the silicate layers. The ABS nanocomposites prepared in this work has been studied by X-ray diffraction, FTIR, transmission electron microscope and thermogravimetric analysis. The effect of using homogenizer on the characteristics of the nanocomposites also has been investigated and discussed in several parts of the present work.     

Toughening of poly(butylene terephthalate) with epoxy-functionalized acrylonitrile-butadiene-styrene

Glycidyl methacrylate (GMA) functionalized acrylonitrile-butadiene-styrene (ABS) copolymers have been prepared via an emulsion polymerization process. These functionalized ABS copolymers (ABS-g-GMA) were blended with poly(butylene terephthalate) (PBT). DMA result showed PBT was partially miscible with ABS and ABS-g-GMA, and DSC test further identified the introduction of GMA improved miscibility between PBT and ABS. Scanning electron microscopy (SEM) displayed a very good dispersion of ABS-g-GMA particles in the PBT matrix compared with the PBT/ABS blend when the content of GMA in PBT/ABS-g-GMA blends was relatively low (<8 wt% in ABS-g-GMA). The improvement of the disperse phase morphology was due to interfacial reactions between PBT chains end and epoxy groups of GMA, resulting in the formation of PBT-co-ABS copolymer. However, a coarse, non-spherical phase morphology was obtained when the disperse phase contained a high GMA content (≥8 wt%) because of cross-linking reaction between the functional groups of PBT and GMA. Rheological measurements further identified the reactions between PBT and GMA. Mechanical tests showed the presence of only a small amount of GMA (1 wt%) within the disperse phase was sufficient to induce a pronounced improvement of the impact and tensile properties of PBT blends. SEM results showed shear yielding of PBT matrix and cavitation of rubber particles were the major toughening mechanisms.     

Controllable synthesis of calcium carbonate polymorphs at different temperatures

Calcium carbonate with various structures and morphologies were prepared by double injection of the CaCl₂ and NH₄HCO₃ solutions with molar ratio of 1:1 at 30-80 °C. The lamellar vaterite particles, the mixture composed of vaterite, aragonite and calcite, and the aragonite whiskers were formed at 30-40 °C, 50-70 °C and 80 °C, respectively. Thermodynamic calculation showed that the value of [CO₃²⁻]/[Ca²⁺] decreased with the increase of temperature, which may be one of the reasons for the formation of the lamellar vaterite at 30-40 °C and the aragonite whiskers at 80 °C.     

Modification of calcium carbonate surface properties: macroscopic and microscopic investigations

Understanding the wettability of mineral powders and its modification by the addition of various surface active agents is crucial for many industrial applications. In many cases, wettability is investigated by macroscopic characterization techniques. In this framework, we decided to study non-porous calcium carbonate powders coated by known amounts of water-repellent molecules. A detailed characterization of the interface, focusing on the analysis of surface heterogeneity, was carried out using water vapor, nitrogen, and argon adsorption. It clearly reveals specific adsorption sites for water-repellent molecules. Wettability and immersion enthalpy measurements show that saturation of the carbonate surface by water-repellent molecules is not necessary for obtaining maximum hydrophobicity. It is reached for approximately one-third of surface saturation; at that point, some high-energy surface sites are still available for water and nitrogen adsorption. This suggests that wettability is not only linked to the availability of surface sites for water molecules.     

改性纳米碳酸钙用于硅酮胶挤出性研究

采用碳化法合成纳米碳酸钙,在反应过程中,调整反应起始温度合成不同晶型大小的纳米碳酸钙。通过透射电镜（TEM）、激光粒度仪对碳酸钙的物相、形貌、粒度进行分析,将改性纳米碳酸钙应用于硅酮胶基料制备及挤出性研究,分析改性纳米碳酸钙的颗粒大小、分散性、流变性能及表面改性剂对挤出性的影响。结果表明：粒径介于50~90 nm,屈服值介于66.4~148.9 Pa,黏度介于0.5~0.75 mPa·s,硬脂酸钠与LH-2、LH-3两种包覆剂进行复配改性的纳米碳酸钙用于硅酮胶基料具有较好的挤出性能。