Increasing CaCO3 Content Research Articles

Degradability of expanded starch/PVA blends prepared using calcium carbonate as the expanding inhibitor

AbstractIn this study, expanded starch/poly(vinyl alcohol) (PVA) blends for packing material were prepared by using calcium carbonate as the expansion inhibitor to investigate the degradability and the structural and mechanical properties of expanded starch/PVA/calcium carbonate blends (ESPCs). The structure of ESPCs became more compact with increasing CaCO3 content and at least 2 parts of CaCO3 were required to obtain the sufficient inhibiting effect on the expansion. As CaCO3 content increased from 1 to 4 parts, tensile strength more than doubled from 70 to 180 KPa, while elongation at break increased about 1.5‐fold. The moduli of ESPCs also increased with increasing CaCO3 content, but they decreased continuously with exposure to UV radiation over all periods of exposure and remained in the range of 10–15 KPa after exposure for 7 weeks. The weight loss of ESPCs due to exposure to soil environment increased with exposure time and the final weight loss after the 5‐week exposure was about 25–30%. Specifically, the degradability of ESPC with 20 parts of PVA was 5% higher than that of ESPC with 30 parts of PVA. The water solubility of ESPC with 30 parts of PVA was somewhat higher than that of ESPC with 20 parts of PVA. Furthermore, most of ESPCs began to be degraded thermally at 292°C. © 2004 Wiley Periodicals, Inc. J Appl Polym Sci 93: 911–919, 2004

Effects of calcium carbonate and its purity on crystallization and melting behavior, mechanical properties, and processability of syndiotactic polypropylene

AbstractCalcium carbonate‐filled syndiotactic poly(propylene) (CaCO3‐filled s‐PP) was prepared in a self‐wiping, co‐rotating twin‐screw extruder. The effects of CaCO3 of varying particle size (1.9, 2.8 and 10.5 μm), content (0–40 wt %), and type of surface modification (uncoated, stearic acid‐coated, and paraffin‐coated) on the crystallization and melting behavior, mechanical properties, and processability of CaCO3‐filled s‐PP were investigated. Non‐isothermal crystallization studies indicate that CaCO3 acts as a good nucleating agent for s‐PP. The nucleating efficiency of CaCO3 for s‐PP was found to depend strongly on its purity, type of surface treatment, and average particle size. Tensile strength was found to decrease, while Young's modulus increased, with increasing CaCO3 content. Both types of surface treatment on CaCO3 particles reduced tensile strength and Young's modulus, but improved impact resistance. Scanning electron microscopy (SEM) observations of the fracture surfaces for selected CaCO3‐filled s‐PP samples revealed an improvement in CaCO3 dispersion as a result of surface treatment. Finally, steady‐state shear viscosity of CaCO3‐filled s‐PP was found to increase with increasing CaCO3 content and decreasing particle size. © 2004 Wiley Periodicals, Inc. J Appl Polym Sci 92: 201–212, 2004

Origin and palaeo‐environments of calcareous sediments in the Moshaweng dry valley, southeast Botswana

AbstractQuaternary sedimentation in the Moshaweng dry valley of southeastern Botswana is evaluated on the basis of geomorphological evolution and sedimentological analyses. Stratigraphic evidence reveals an upper surface (1095 m) containing abundant sil‐calcrete, an intermediate surface (1085 m) in which sil‐calcrete underlies nodular calcrete and lower (1075 m) surface in which sil‐calcrete and nodular calcrete are interbedded. This subdivision is reflected in the geochemical composition of the sediments which show an overall trend of decreasing SiO2 content (and increasing CaCO3 content) with depth from the highest to the lowest surface levels. The calcretes and sil‐calcretes represent modifications of pre‐existing detrital Kalahari Group sand and basal Kalahari pebbles which thinned over a Karoo bedrock high. Modification took place during wet periods when abundant Ca++‐rich groundwater flowed along the structurally aligned valley system. With the onset of drier conditions, water table fluctuations led to the precipitation of nodular calcretes in the phreatic layer to a depth of about 20 m. A major geochemical change resulted in the preferential silicification of the nodular calcrete deposits. Conditions for silica mobilization may be related to drying‐induced salinity and in situ geochemical differentiation brought about by pebble dissociation towards the top of the sediment pile. As calcretization and valley formation progressed to lower levels, silica release took place on a diminishing scale. Thermoluminescence dating infers a mid‐Pleistocene age for sil‐calcrete formation suggesting that valley evolution and original calcrete precipitation are much older. Late stage dissolution of CaCO3 from pre‐existing surface calcretes or sil‐calcretes led to the formation of pedogenic case‐hardened deposits during a time of reduced flow through the Moshaweng system possibly during the upper or late Pleistocene. Copyright © 2002 John Wiley & Sons, Ltd.

Structural analysis of oriented poly(ε‐caprolactone) including CaCO3 particles with 13C solid‐state NMR

AbstractThe results of a study of the relation between the oriented structure and drawn Poly(ε‐caprolactone) specimens including CaCO3 particles and their dynamic mechanical properties are presented. The loss elasticity, E″, showed almost the same curve for both undrawn sheets and drawn sheets as a function of CaCO3 content. On the other hand, the storage modulus, E′, of drawn sheets increased nonlinearly with increasing CaCO3 content, and their curve showed lower E′ values than those of undrawn sheets. By simulation of 13C CP NMR spectra of drawn PCL/CaCO3 sheets, both oriented and unoriented components were observed. The distribution parameter, p, of drawn PCL/CaCO3 sheets was 13°, which was larger than those (8°) of drawn PCL. Further, the fraction of the unoriented component increased with increasing CaCO3 content. Thus, adding CaCO3 particles into the PCL, the arrangement of the oriented component was disturbed and decreased. In addition, from the line shape analyses of 13C CP MAS NMR spectra, four peaks were obtained in not only undrawn sheets but also in drawn sheets of both PCL and PCL/CaCO3 compounds. Besides, structural change occurred at only drawn PCL/CaCO3 sheets. Therefore, the change in dynamic mechanical properties observed only for drawn PCL/CaCO3 sheets were strongly dependent on the orientational structure, which was formed under shear stress of the stretching drawn process. © 2001 John Wiley & Sons, Inc. J Appl Polym Sci 80: 2376–2382, 2001

Effect of wheat root exudates on mobilization of iron and zinc from calcareous soils

To study the influence of phytosiderophores (PS) released from some Egyptian wheat cultivars on mobilization and absorption of iron (Fe) and zinc (Zn) from pre‐amended calcareous soils, three selected wheat cultivars (Sids 10, Giza 162, and Baniswaif 2) were used. The cultivars were pre‐cultured for 17 days in nylon bags as the control root compartment (RC) and filled with fine sand and provided with nutrient solution +/‐ Fe‐EDTA. The nylon bags with roots of the seedlings were brought in contact for further 4 days with pre‐amended calcareous soils. DTPA‐extractable Fe and Zn from amended calcareous soils with sludge was much higher than from untreated soils. Relative increases in extractable Fe or Zn were found in Fe‐deficient wheat (‐Fe pretreatment) compared with Fe‐sufficient plants. The extractable amounts of Fe‐ and Zn‐DTPA from different calcareous soils were affected by the distance from the central root compartment where minimum values were reached at distance of more than 4 mm. Release of PS and mobilization of Fe and Zn were highest with, Sids 10 and Baniswaif 2 cultivare while Giza 162 was lower particularly under sufficient seedlings. Moreover, increasing CaCO3 content in calcareous soils minimized the growth differences among wheat cultivars. The status of Fe and Zn contents was improved in roots compared with shoots during the 4‐day growth period. Furthermore, nutrient status was generally higher in soils amended with sludge compared with untreated soils. Sids 10 have the highest values of Fe content particularly under Fe‐deficient conditions while Giza 162 was inferior. Zinc content in Sids 10 was superior in high calcareous soil (53% CaCO3 content) while Baniswaif 2 was superior in low calcareous soil (14% CaCO3 content).

Influence of calcium carbonate on the dissolution of Sechura phosphate rock in soils

Different amounts of CaCO3 (5.3 to 20% w/w) (180-75µm) were mixed with Sechura phosphate rock (SPR) (180-75µm) and incubated with Davidstow and Withnell soils. These soils differ in their proton supply and Ca-buffering capacity. The Ca-buffering capacity of Davidstow soil was also changed by adding different amounts of cation-exchange resin (CER). The consumption of protons and the release of Ca during the preferential dissolution of CaCO3 decreased the dissolution of the SPR (measured by P release). However, the negative effect of CaCO3 on SPR dissolution at near equilibrium (60 d) depended on both the proton supply and Ca-sink size of the soil. The Davidstow soil had an adequate proton supply (43.6 mmol H kg−1 pH unit−1) but a small Ca sink (32.0 mmol kg−1), and the dissolution of SPR at 60 d decreased linearly from 27.5 to 19.5% with increasing CaCO3 content. The Withnell soil had an adequate Ca sink (75.5 mmol kg−1) but a small proton supply (21.4 mmol H kg−1 pH unit−1), and the amount of P dissolved at 60 d also decreased (from 49 to 35%) with increasing CaCO3 content. Adding CER to the Davidstow soil increased the Ca-sink size from 32.0 to 39.0 mmol kg−1 and almost prevented the decrease in SPR dissolution with increasing CaCO3 content. This suggests that, in soils with an adequate proton supply and Ca-sink size, CaCO3 present as an accessory mineral in PR materials has a negligible effect on the dissolution of the PR.

The stability of iron chelates in calcareous soils

AbstractThe stability of Fe‐EDTA and Fe‐CDTA was investigated in order to evaluate their effectiveness under calcareous soil conditions. To accomplish this evaluation the reaction rate of fixation, K, the adsorption coefficient, Kd, and the retardation factor, S, of the iron chelate were determined through column experiments at pH 7.8 and two ionic strengths, I, of CaCl2.The results indicated that iron in Fe‐EDTA was more fixed than in Fe‐CDTA. The fixation increased by increasing the ionic strength. Also it increased linearly with increasing CaCO3 content of the soil.The values of retardation factor, S, showed that this parameter depended more on the surface area of the soil than on I or CaCO3 content. The product KS depends on CaCO3 content, surface area of the soil, ionic strength and chelating agent used. It can be taken as an index for the efficiency of the iron chelate under different conditions.Fe‐EDTA was more adsorbed than Fe‐CDTA, the adsorption increased with increasing ionic strength and surface area of the soil.