Increasing CaCO3 Content Research Articles

Assessment of New Bio-Cement Method for Sand Foundation Reinforcement

Microbially induced carbonate precipitation (MICP) is a new method used in recent years to improve the soil. However, this method still faces challenges related to low grouting reinforcement strength and efficiency. In this study, both the bio-cement infiltration method and bio-cement mixed method for sand foundation were proposed, and physical model tests were conducted to investigate the mechanical properties of sand treated with the bio-cement method. The results showed that the bio-cement maximized the utilization rate of bacterial liquid and reduced the waste caused by the loss of bacteria compared with traditional methods. Both the size of the reinforced area and bearing capacity of the sand reinforced by bio-cement infiltration method were controlled by the volume ratio of the bio-cement, calcareous sand powder, and the inflow rate. The maximum bearing capacity was 125 N when using a mixture of bio-cement and calcareous sand powder with a ratio of 400/80, with an inflow rate of 20 mL/min. The UCS of the sand reinforced by the bio-cement mixed method gradually decreased from 3.44 MPa to 0.88 MPa with depth, but increased with increasing CaCO3 content. The CaCO3 crystals were primarily concentrated at the contact point between the particles, and the formed crystals were mainly polyhedral. Reduction in the CaCO3 content mainly occurred in the central deep part of the reinforcement area. The result provides an experimental basis for the use of bio-cement in the reinforcement of sand soil foundations.

Biodegradable PBAT/PLA/CaCO3 Blowing Films with Enhanced Mechanical and Barrier Properties: Investigation of Size and Content of CaCO3 Particles

AbstractBiodegradable poly(butylene adipate‐co‐terephthalate)/poly(lactic acid)/calcium carbonate (PBAT/PLA/CaCO3) blend films with variable compositions are prepared using one‐step melt‐blending and a following film‐blowing. The effects of CaCO3 content and particle size on the physicochemical properties of the films are investigated. The rheology results demonstrate that the storage modulus and complex viscosity are increased with the increasing CaCO3 content. The tensile performance and tear resistance including both the machine direction (MD) and transverse direction (TD) are also improved by adding CaCO3. Especially, P7/P3/C300030 achieves the highest tensile and tearing strength in MD of 31 ± 2.5 MPa and 99 ± 4.0 N mm−1, respectively. Compared with unfilled PBAT/PLA films, the water vapor transmission greatly declines from 621 to 287 g m−2 24 h and the oxygen transmission values are also reduced from 1400 to 1010 cm3 m−2 d Pa after the incorporation of CaCO3 particles. A slight decrease in thermal stability is detected in PBAT/PLA/CaCO3, but overall, the decomposition temperature is much higher than the processing and service temperature. Therefore, the biodegradable PBAT/PLA films with low‐cost CaCO3 fillers demonstrate excellent mechanical and oxygen and moisture barrier performance, which show great potentials in food‐packaging and mulch film in the agriculture field.

Combination Effects of Calcium Carbonate and Crumb Rubber Fillers on the Properties of Natural Rubber Latex Foams

The preparation and mechanical properties of natural rubber latex foam (NRLF) using calcium carbonate (CaCO3) or combinations of CaCO3 and crumb rubber (CRM) as fillers were investigated. The CaCO3 contents were varied as 10, 20, and 30 phr. The ratios of CaCO3/CRM at 0.5/1.0, 0.75/0.75 and 1.0/0.5 were used. The experimental findings were that CaCO3 was well dispersed and blended with the natural rubber latex. The density of the NRLF increased with the increase in CaCO3 content. The foam containing less than 20 phr of CaCO3 showed higher tensile strength and elongation at the break than natural rubber latex foam without CaCO3. The percentage of compression set and depression of NRLF increased with increasing CaCO3 content. When the mixture of CaCO3 and CRM was used as a filler in NRLF, it was found that both CaCO3 and CRM were well dispersed and mixed with natural rubber latex. The NRLF containing the mixture of CaCO3 and CRM was more flexible than the foam containing only CaCO3. Furthermore, the NRLF with CaCO3 and CRM at the ratio of0.75/0.75 showed more uniform bubble shape and higher density than foam with other CaCO3/CRM ratios. The tensile strength of the foam decreased with decreasing CRM content, while the percentage of depression was low when the proportion of the CRM was reduced. Furthermore, the foam containing CaCO3/CRM ratio of 0.75/0.75 showed the lowest compression set.

Adsorption of Heavy Metals on Soil Collected from Lixisol of Typical Karst Areas in the Presence of CaCO3 and Soil Clay and Their Competition Behavior

The content of heavy metals in the soil in Guizhou Province, which is a high-risk area for heavy metal exposure, is significantly higher than that in other areas in China. Therefore, the objective of this study was to evaluate the ability of CaCO3 and clay to accumulate heavy metals in topsoil sample collected from Lixisol using the method of indoor simulation. The results showed that the contents of Cu, Zn, Cd, Cr, Pb, Hg and As in the soil sample were 10.8 mg/kg, 125 mg/kg, 0.489 mg/kg, 23.5 mg/kg, 22.7 mg/kg, 58.3 mg/kg and 45.4 mg/kg, respectively. The soil pH values increased with the CaCO3 concentration in the soil, and the fluctuation of the soil pH values was weak after the CaCO3 concentrations reached 100 g/kg. The adsorption capacity of lime soil increased by approximately 10 mg/kg on average, and the desorption capacity decreased by approximately 300 mg/kg on average. The desorption of all heavy metals in this study did not change with increasing clay content. Pseudo-second-order kinetics were more suitable for describing the adsorption kinetics of heavy metals on the soil material, as evidenced by the higher R2 value. The Freundlich model can better describe the adsorption process of As on lime soil. The process of As, Cr, Cd and Hg adsorption on the soil sample was spontaneous and entropy-driven. Additionally, the process of Cu and Pb adsorption on the soil materials was spontaneous and enthalpy-driven. Generally, the adsorption and desorption of heavy metals in polluted soil increased and decreased, respectively, with increasing CaCO3 content. The effect of calcium carbonate on the accumulation of heavy metals in soil was greater than that of clay. In summary, CaCO3 and pH values in soil can be appropriately added in several areas polluted by heavy metals to enhance the crop yield and reduce the adsorption of heavy metals in soils.

Plugging High-Permeability Zones of Oil Reservoirs by Microbially Mediated Calcium Carbonate Precipitation.

Simple plugging of the high-permeability “thief zones” of oil reservoirs is the most plausible and also the most straightforwardly achievable approach to enhance sweep efficiency and oil recovery. Sporosarcina pasteurii is a representative microorganism with the ability to precipitate calcium carbonate (CaCO3) via enzymatic hydrolysis of urea in the presence of calcium ions. Microbially induced calcium carbonate precipitation (MICP) can cement and seal the granular and fractured media and thus can be used as a potential microbial plugging agent for the high-permeability zones of oil reservoirs. The following investigated the microscopic characteristics of MICP plugging and its efficacy in permeability reduction. The columns of near-spherical silica sand and angular silica sand with three separate granularities (40/60, 60/80, and 80/120 mesh) were used as artificial rock cores representing distinct pore sizes and pore characteristics to investigate the efficacy and microprocess of MICP plugging with different biotreatment periods. The results indicated that permeability is reduced significantly after only short periods of biotreatment. After eight cycles of MICP treatments, the permeability for each type of cores dropped by 54–90% of individual initial permeabilities. The measured CaCO3 content indicated that the decreasing rate in permeability with the increasing CaCO3 content experiences three contrasting stages, namely, slow decline, speedy decline, and plateauing. X-ray diffraction indicated that most of the generated CaCO3 crystals occur as vaterite with only a small amount of calcite. Imaging by scanning electron microscopy further revealed the microprocess of MICP plugging. Microorganisms first concentrate on the pore wall to secrete CaCO3, forming a thin and large uniform layer of CaCO3. Then, some nucleation sites of CaCO3 crystals will experience further preferential growth, resulting in large, dominant crystals that act as a plugging agent within the pore space. Compared to extracellular polymeric substances, which are currently the primary microbial plugging agent used to enhance sweep efficiency of oil reservoirs, bio-CaCO3 appears more effective in plugging in terms of its morphology, size, and growth characteristics.

Effects of calcium carbonate on hydro-mechanical properties of bentonite

To simulate characteristic changes of the bentonite mixing with CaCO3 crystals that precipitate from groundwater around the high-level radioactive waste repositories, different amounts of CaCO3 powders were mixed in the bentonite. In this study, four series of bentonite/CaCO3 mixtures were prepared with different contents of CaCO3 powders. A series of swelling, compression and direct shear tests were conducted on the bentonite/CaCO3 samples using deionized water. Terzaghi consolidation theory was adopted to compute the hydraulic conductivity of bentonite/CaCO3 mixtures. The results demonstrated that the final swelling strain decreased with increasing vertical stress and the content of CaCO3 powders. The compression index decreased slightly with increasing CaCO3 content. It was found that as the CaCO3 content increased, the hydraulic conductivity of bentonite/CaCO3 mixtures decreased. There was a peak point in the shear strength of unsaturated samples with the differences of the CaCO3 content. The cohesion of unsaturated samples increased first and then decreased, but saturated samples presented the opposite character. It could be seen from the scanning electron micrograph that the existence of CaCO3 powders filled pores of bentonite/CaCO3 mixtures and made the structure denser.

Structural characteristics and its influencing factors of typical loess

The aim of this study was to analyze the influences of water content, calcium carbonate (CaCO3) content, and dry density on the structural characteristics of typical loess, using comprehensive structure potential (CSP) as the structural parameter. Oedometer testing was conducted on undisturbed, saturated, and disturbed loess samples under various conditions of water content, CaCO3 content, and dry density to obtain the deformation data. Based on the collected data, we calculated the CSP and analyzed the structural properties of the samples. The weight of each influencing factor was quantified using a variation coefficient method. To analyze the evolution mechanism of soil structural properties, we determined the microstructure of the samples by scanning electron microscopy studies and mercury intrusion porosimetry. The results showed that the CSP increased with decreasing water content, increasing CaCO3 content, and decreasing dry density. Water content had the greatest effect on the CSP, and CaCO3 content had the least effect. There were two kinds of changes in the structural properties of samples under different conditions: strengthening and weakening. Large pores exerted a significant influence on soil structural properties.

Validation of water sorption‐based clay prediction models for calcareous soils

AbstractSoil particle size distribution (PSD), particularly the active clay fraction, mediates soil engineering, agronomic and environmental functions. The tedious and costly nature of traditional methods of determining PSD prompted the development of water sorption‐based models for determining the clay fraction. The applicability of such models to semi‐arid soils with significant amounts of calcium carbonate and/or gypsum is unknown. The objective of this study was to validate three water sorption‐based clay prediction models for 30 calcareous soils from Iran and identify the effect of CaCO3 on prediction accuracy. The soils had clay content ranging from 9 to 61% and CaCO3 from 24 to 97%. The three water sorption models considered showed a reasonably fair prediction of the clay content from water sorption at 28% relative humidity (RMSE and ME values ranging from 10.6 to 12.1 and −8.1 to −4.2, respectively). The model that considers hysteresis had better prediction accuracy than the other two that do not. Moreover, the prediction errors of all three models arose from under‐prediction of the clay content. The amount of hygroscopic water scaled by clay content decreased with increasing CaCO3 content. The low organic carbon content of the soils and the low fraction of low‐activity clay minerals like kaolinite suggested that the clay content under‐predictions were due to large CaCO3 contents. Thus, for such water‐sorption based models to work accurately for calcareous soils, a correction factor that considers the reduction of water content due to large CaCO3 content should be included.

Melt processing of maleic anhydride grafted poly(lactic acid) and its compatibilizing effect on poly(lactic acid)/poly(butylene adipate-co-terephthalate) blend and their composite

Poly(lactic acid) (PLA)/poly(butylene adipate-co-terephthalate) (PBAT) blends were prepared using melt processing. The effects of maleic anhydride grafted PLA (PLA-g-MA) and calcium carbonate (CaCO3) content on mechanical, thermal, and morphological properties of the blends were investigated. PLA-g-MA was synthesized by varying monomer and initiator contents using a reactive melt-grafting process. Tensile properties of PLA/PBAT blend were enhanced with adding 2 phr of PLA-g-MA. SEM micrographs exhibited the improvement of interfacial adhesion between PLA and PBAT in the compatibilized blend. Moreover, thermal stability of the blends improved with presence of PLA-g-MA. With increasing CaCO3 content, Young’s modulus of the composites increased.

Evaluation of fracture behavior of polyethylene/CaCO3 nanocomposite using essential work of fracture (EWF) approach

The fracture behavior of two series of polyethylene (PE) films, both the unreinforced and reinforced with different amounts of nanoscale calcium carbonate (CaCO3) particles was investigated in this research work by means of the essential work of fracture (EWF) approach under the loading condition of mode I. For this purpose, EWF test was conducted on deeply double edge notched tension (DDENT) specimens; and the essential and non-essential components of fracture work, were estimated using the plots representing the variation of the specific total work of fracture (wf) versus the ligament length of the specimen. The results showed that the crack resistance for the PE/CaCO3 nanocomposites was lower than that of the unreinforced PE, and for the case of nanocomposite samples, the total plastic energy absorbed during fracture increased with increasing CaCO3 content up to 2·5 wt-% and then decreased for nanocomposite samples containing 5 wt-%CaCO3. The plastic zone size decreased with increasing CaCO3 content, whereas the specific plastic work per unit volume increased with increasing weight percent CaCO3. The observed trends were rationalized using the fracture and deformation mechanisms of nanocomposites.

Late Glacial–early Holocene environmental changes in Charzykowskie Lake (northern Poland) based on oxygen and carbon isotopes and Cladocera data

Based on isotopic and cladoceran investigations of a 6-m-long sediment core, a reconstruction of paleoenvironmental dynamics in Charzykowskie Lake (northern Poland) is proposed. The sediments consist of sandy silts at the bottom, followed (in upward succession) by gyttja characterized by increasing CaCO3 content. The measured δ18O values oscillate from −9.3 to −5‰ and δ13C from – 5.7 to +0.4‰. We identify 24 taxa of subfossil Cladocera and six phases (CAZ) of faunal development. Isotopic and cladoceran data together with detrended correspondence analyses (DCA) allow reconstruction of the environmental conditions, particularly changes in water level, temperature, and trophic status, during the Late Glacial and early Holocene. The lowest water temperature, connected with the inflow of cold melt water, occurred in the Late Glacial and Preboreal period. Since the Boreal period, gradual warming is observed and expressed through a positive trend in both δ18O and δ13C values and changes in Cladocera species assemblages. The lake was deepest at the beginning of the Holocene as a result of dead ice melting (supply of melt water; lowering of lake bottom) and/or precipitation increase (change in atmospheric circulation). During the Boreal period, the fall in water level takes place despite the opposite trend observed at nearby sites. In addition, the cladoceran data indicate an initial decrease in trophic conditions from α-mesotrophic to oligotrophic and then an increase to the β-mesotrophic state.

Morphology, Crystallization and Dynamical Mechanical Behavior of iPP/Nano-CaCO3 Composites

This article describes our study of crystallization behavior of nano-CaCO3-filled polypropylene under nonisothermal from the melt by differential scanning calorimetry (DSC). Morphology observation indicated with increasing CaCO3 content the aggregates increased. Nano-CaCO3 acted as nucleating site during nonisothermal crystallization in all iPP/nano-CaCO3 composites. For nonisothermal crystallization kinetic studies, the result indicated that the Jeziorny and Ozawa approach cannot adequately describe the nonisothermal crystallization kinetic of iPP composite. In addition, Mo equation was employed to describe the nonisothermal crystallization kinetic process with satisfied results. Dynamic mechanical analysis indicated with increasing CaCO3 content the glass transition decreased slightly.

Effect of calcium carbonate on hardening, physicochemical properties, and in vitro degradation of injectable calcium phosphate cements

The main disadvantage of apatitic calcium phosphate cements (CPCs) is their slow degradation rate, which limits complete bone regeneration. Carbonate (CO₃²⁻) is the common constituent of bone and it can be used to improve the degradability of the apatitic calcium phosphate ceramics. This study aimed to examine the effect of calcite (CaCO₃) incorporation into CPCs. To this end, the CaCO₃ amount (0-4-8-12 wt %) and its particle size (12.0-μm-coarse or 2.5-μm-fine) were systematically investigated. In comparison to calcite-free CPC, the setting time of the bone substitute was delayed with increasing CaCO₃ incorporation. Reduction of the CaCO₃ particle size in the initial powder increased the injectability time of the paste. During hardening of the cements, the increase in calcium release was inversely proportional to the extent of CO₃²⁻ incorporation into apatites. The morphology of the carbonate-free product consisted of large needle-like crystals, whereas small plate-like crystals were observed for carbonated apatites. Compressive strength decreased with increasing CaCO₃ content. In vitro accelerated degradation tests demonstrated that calcium release and dissolution rate from the set cements increased with increasing the incorporation of CO₃²⁻, whereas differences in CaCO₃ particle size did not affect the in vitro degradation rate under accelerated conditions.

Mechanical properties, thermal stability, and crystallization kinetics of poly(3‐hydroxybutyrate‐co‐4‐hydroxybutyrate)/calcium carbonate composites

AbstractBacterial polyester poly(3‐hydroxybutyrate‐co‐4‐hydroxybutyrate) (P3/4HB) containing 5 mol% 4HB was composited with different calcium carbonate (CaCO3) fillers. The effect of CaCO3 contents on thermal properties, mechanical property, and crystallization kinetics was evaluated. The thermal stability of P3/4HB was reduced by mixing with CaCO3 particles. With increasing CaCO3 content, the elongation at break, tensile strength, and impact strength decrease; however, elastic modulus increases. When P3/4HB with 20 mol% 4HB was added into the P3/4HB/CaCO3 composite, the impact strength were enhanced significantly; however, the elongation at break and tensile strength were only slight to moderate improvements. However, when compared with nano‐ and light‐CaCO3, heavy CaCO3 had the best mechanical properties. The nonisothermal and isothermal crystallization results demonstrated that the crystallization rate of P3/4HB was reduced and the highest crystallinity was obtained for all kinds of CaCO3 fillers at 40 phr content. POLYM. COMPOS., 2011. © 2011 Society of Plastics Engineers

Properties of Biodegradable Poly(lactic acid)/Poly(butylene adipate-co-terephthalate)/Calcium Carbonate Composites

Poly (lactic acid) (PLA), a biodegradable polyester, derived from renewable resources has been widely used in biomedical and packaging applications. However, the shortcomings for using PLA including its processing instability, low melt viscosity and low flexibility limited its applications. To overcome these shortcomings, poly (butylene adipate-co-terephthalate) (PBAT) was blended with PLA to improve ductility of PLA. However, PLA and PBAT are incompatible. Maleic anhydride grafted PLA (PLA-g-MA) was used to enhance the compatibility of the blends. Moreover, the blend of PLA and PBAT exhibited higher elongation at break but lower tensile strength and Young’s modulus than the pure PLA due to the addition of a ductile phase. Therefore, the addition of calcium carbonate (CaCO3) to PLA/PBAT blends led to achieve balanced properties of the blends. In this study, PLA/PBAT blends and PLA/PBAT/CaCO3 composites were prepared by an internal mixer. PLA-g-MA was as a compatibilizer. Mechanical properties and rheological properties of the blend and composites were investigated. In addition, morphologies of PLA/PBAT blend and their composites were observed by a scanning electron microscope (SEM). The incorporation of PBAT gave rise to remarkable improvement in elongation at break and impact strength of PLA. Tensile strength of PLA/PBAT blend was enhanced by adding PLA-g-MA. With increasing CaCO3 content, Young’s modulus of the composites increased while tensile strength and elongation at break decreased.

Biomass Carbon Ratio of Polymer Composites Measured by Accelerator Mass Spectrometry

The evaluation method of biomass carbon ratio of polymer composite samples including organic and inorganic carbons individually was investigated. Biodegradable plastics and biobased plastics can have their mechanical properties improved by combining with inorganic fillers. Polymer composites consisting of biodegradable plastics and carbonate were prepared by two different methods. Poly(lactic acid) (PLA) composite was prepared by synthesis from l-lactide with catalyst and calcium carbonate (CaCO3) powders from lime. Poly(butylene succinate) (PBS) composite was prepared by hot-pressing the mixture of PBS powder and CaCO3 powders from oyster shells. The mechanical properties of composite samples were investigated by a tensile test and a compression test using an Instron type mechanical tester. Tensile test with a dumbbell shape specimen was performed for PBS composite samples and compression test with a column shape specimen for PLA composite samples. Strength, elastic modulus and fracture strain were obtained from the above tests. Biomass carbon ratio is regulated in the American Standards for Testing and Materials (ASTM). In ASTM standards on biomass carbon ratio, it is required that carbon atoms from carbonates, such as CaCO3, are omitted. Biomass carbon ratio was evaluated by ratio of 14C to 12C in the samples using Accelerator Mass Spectrometry (AMS). The effect of pretreatment, such as oxidation temperature and reaction by acid, on results of biomass carbon ratio was investigated. Mechanical properties decrease with increasing CaCO3 content. The possibility of an evaluation method of biomass carbon ratio of materials including organic and inorganic carbons was shown.

Biodegradable thermoplastic elastomer comprising PLLCA and CaCO3 whiskers: mechanical properties, thermal stability and shape memory properties

A biodegradable and thermoplastic elastomer—poly(L-lactide-co-e-caprolactone) (PLLCA)—was reinforced with 5, 10, 20, and 30 wt% of CaCO3 whiskers. We assessed the influence of the CaCO3 whisker content on the mechanical and thermal properties of the PLLCA/CaCO3 whisker composites. Scanning electron microscopy (SEM) revealed that the CaCO3 whiskers were uniformly distributed in the composite matrices. The results of differential scanning calorimetry (DSC) and dynamic mechanical analysis (DMA) showed that the glass transition temperatures (T g) of the composites increased slightly with increasing CaCO3 whisker content. At low CaCO3 whisker contents, the tensile strengths of the composites increased sharply with increasing CaCO3 content, the Young’s moduli also increased, and the elongation at break values gradually decreased. Thermogravimetric analysis (TGA) showed that the CaCO3 whiskers can promote the thermal degradation of PLLCA. Shape memory test results indicated that an appropriate amount of CaCO3 whiskers can improve the shape memory properties of PLLCA.

Rheological and isothermal crystallization characteristics of neat and calcium carbonate‐filled syndiotactic polypropylene

AbstractSteady‐state and oscillatory shear behavior of three neat syndiotactic polypropylene (s‐PP) resins and a s‐PP resin (s‐PP#8) filled with CaCO3 particles of varying content, size, and type of surface modification were investigated. All of the neat s‐PP resins investigated exhibited the expected shear‐thinning behavior. Both the storage and loss moduli increased with decreasing temperature. The shift factors used to construct the master curves were fitted well with both the Arrhenius and the Williams–Landel–Ferry (WLF) equations. The inclusion of CaCO3 particles of varying content, size, and type of surface modification, to a large extent, affected both the steady‐state and oscillatory shear behavior of s‐PP/CaCO3 compounds, with the property values being found to increase with increasing content, decreasing size, and surface coating of the CaCO3 particles. Lastly, the effects of melt‐annealing and crystallization temperatures on isothermal crystallization behavior of s‐PP#8 filled with CaCO3 particles of varying content, size, and type of surface modification were also investigated. The half‐time of crystallization of neat s‐PP#8 exhibited a strong correlation with the choice of the melt‐annealing temperature (Tf) when Tf was less than about 160 °C, while it became independent of Tf when Tf was greater than about 160 °C. On the other hand, the half‐time of crystallization of s‐PP#8/CaCO3 compounds did not vary much with the Tf. Generally, the observed half‐time of crystallization decreased with increasing CaCO3 content and increased with increasing CaCO3 particle size. Finally, coating the surface of CaCO3 particles with either stearic acid or paraffin reduced the ability of the particles to effectively nucleate s‐PP#8. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 100: 4515–4525, 2006

Effect of calcium carbonate on the mechanical and thermal properties of isotactic polypropylene/ethylene vinyl acetate blends

AbstractThe effect of calcium carbonate (CaCO3) on the mechanical properties (with heat treatment) and thermal properties of polypropylene and isotactic polypropylene (i‐PP)/ethylene vinyl acetate (EVA) blends was investigated. CaCO3, in five different concentrations (3, 6, 9, 12l, and 15 wt %), was added to i‐PP/EVA (88/12) to produce ternary composites. The mechanical properties, including the yield and tensile strengths, elastic modulus, Izod impact strength for notch radii of 0.25 and 1 mm, and hardness with and without an annealing heat treatment, and the thermal properties, such as the melting point and melt‐flow index, of the composites were investigated. The annealing heat treatment was carried out at 100°C for three different holding times: 75, 100, and 150 h. On the basis of the results, attempts were made to establish a relationship between the CaCO3 content, the annealing holding time, and the mechanical and thermal properties to obtain the best results. The tensile test results showed that the heat treatment was not effective for the ultimate tensile strength, and the yield strength and tensile strength decreased gradually as the CaCO3 content increased. However, CaCO3 was effective for higher elastic modulus, impact strength, and hardness values. A considerable increase in the elastic modulus was found with a 3% CaCO3 concentration for a holding time of 100 h. The maximum impact strength for a notch radius of 1 mm was obtained with 3% CaCO3 with annealing for a holding time of 100 h, whereas a 9% CaCO3 concentration produced higher toughness values for a notch radius of 0.25 mm. The fracture surfaces also supported the results from the Izod impact tests. Similarly, hardness values increased with the annealing heat treatment and increasing CaCO3 content. However, different holding times showed similar effects on the hardness values. The increased CaCO3 content caused the melting point to increase 5°C, whereas the melt‐flow index showed a sharp decrease as the CaCO3 content increased to 3%. Taking into consideration the mechanical and thermal properties and the annealing holding time, we recommend a CaCO3 concentration of 3% with an annealing heat treatment for 100 h for optimum properties of such ternary composites. © 2005 Wiley Periodicals, Inc. J Appl Polym Sci 96: 1126–1137, 2005

Effects of calcium carbonate as the expanding inhibitor on the structural and mechanical properties of expanded starch/polyvinyl alcohol blends

AbstractIn this study, expanded starch/PVA/CaCO3 blends (ESPCs) were prepared using the pilot system composed of a supermixer and a twin‐screw extruder to investigate the effects of CaCO3 as the expanding inhibitor on the structural and mechanical properties of ESPCs. The pore ratio of ESPCs with the interconnecting open‐cell structure decreased with increasing CaCO3 content and the structure of ESPCs became more compact. The inhibiting process of CaCO3 during the expansion of starch/PVA blends was proposed and certified by FTIR spectroscopy and X‐ray diffraction. At least two parts of CaCO3 were required to obtain a sufficient inhibiting effect on the expansion. The mechanical properties of ESPCs such as tensile strength, elongation at break, modulus, and specific work of rupture were improved by the addition of CaCO3 as the expanding inhibitor. As CaCO3 content increased from one to four parts, the tensile strength increased 2.6‐fold, from 70 to 180 kPa, whereas elongation at break increased about 1.5‐fold. The moduli of ESPCs also increased with increasing CaCO3 content. © 2004 Wiley Periodicals, Inc. J Appl Polym Sci 93: 1762–1768, 2004