Number Of Flocs Research Articles

Measurements of frazil ice flocs in rivers

Abstract. Frazil floc sizes and concentrations have been investigated in a small number of laboratory studies, but no detailed field measurements have been reported previously. In this study, a submersible camera system was deployed a total of 11 times during the principal and residual supercooling phases in the North Saskatchewan, Peace, and Kananaskis rivers to capture time-series images of frazil ice particles and flocs. Images were processed to accurately identify flocs and to calculate their sizes and concentrations. Key hydraulic and meteorological measurements were collected, and air–water heat fluxes were estimated to investigate their influence on floc properties. A lognormal distribution was found to be a good fit for the floc size distribution. The mean floc size ranged from 1.19 to 5.64 mm and the overall mean floc size was 3.80 mm. The mean floc size decreased linearly as the local Reynolds number increased. The average floc number concentration ranged from 1.80×10-4 to 1.15×10-1 cm−3. The average floc volumetric concentration ranged from 2.05×10-7 to 4.56×10-3 and was found to correlate strongly with the fractional height above the river bed. No significant correlations were found between the air–water heat flux and floc properties. Time series analysis showed that during the principal supercooling phase, floc number concentration and mean size increased significantly just prior to peak supercooling and reached a maximum near the end of principal supercooling. During the residual supercooling phase, the mean floc size did not typically vary significantly even 2.5 h after the residual phase had ended and the water temperature had increased above 0 °C.

Effect of biopolymer concentration on the kinetics of marine snow formation

Marine snow floc refers to coagulation of microbes and marine debris in the upper ocean layers, bound together by bio-polymers such as transparent exopolymer particles (TEP) secreted by microbes. The stickiness of TEP plays a crucial role in determining the rate of marine snow floc formation. Additionally, the effect of TEP on the size distribution of marine snow influences the sinking velocity of the flocs. Using a surrogate material system, we study the kinetics of marine snow using a custom-built experimental setup, which allows direct measurement of floc size, floc number density, and floc sinking velocity as a function of TEP concentration. By comparing the experimental floc size with Smoluchowski coagulation theory, we obtain stickiness index, which increases with TEP concentration first, reaches maximum around 0.3 g/L of TEP and decreases upon further increase in TEP concentration. The experimental sinking velocity scales with floc size as ws=adb, with b ranging from 0.57 to 0.68. The exponent is slightly higher than that of 0.5 expected in the Stokes limit. This study establishes a clear link between stickiness index, sinking velocity, and polymer concentration, providing valuable insights for modelling of marine snow dynamics in deep ocean conditions. These findings contribute to a better understanding of the kinetics of marine snow formation, essential for predicting carbon sequestration within the biological carbon pump.

Machine learning framework for modeling flocculation kinetics using non-intrusive dynamic image analysis

The implementation of a machine learning (ML) model to improve both the effectiveness and sustainability of the water treatment system is a significant challenge in the water sector, with the optimization of flocculation processes being a major setback. The objective of this study was to develop a ML model for predicting flocs evolution of the flocculation process in water treatment. Furthermore, we have devised a framework for its potential adoption in large-scale water treatment. Therefore, the paper can be split into two parts. In the first one, flocculation evolution has been studied from an experimental setup, using a non-intrusive image acquisition method. Subsequently, the ML framework has been implemented. Batch assay data of two velocity gradients (Gf 20 and 60 s−1) and flocculation time of three hours were partitioned into five groups for flocs length range 0.27–3.5 mm and upscaled using linear method. Multilayer Perceptron (MLP) and Long-Short Term Memory (LSTM) models, and traditional time series model, Auto Regressive Integrated Moving Average (ARIMA) were explored to predict floc length evolution data. The experiments illustrate the kinetics of flocculation, where the initial stage is characterized by a rapid floc growth followed by a plateau during which floc length fluctuates within a narrow range. Results demonstrate that ML is sensitive to flocculation; however, the model should be selected with care. ARIMA model is not suitable for predicting number of flocs with negative test accuracy (R2). In contrast, MLP recorded R2 of 0.86–1.0 for training and 0.92–1.0 for testing, across Gf 20 s−1 and Gf 60 s−1. LSTM model has the best prediction R2 of 0.92–1.00 for Gf 20 s−1 and accurately predicts the number of flocs across all groups and Gfs. Our study has proven that the developed framework could be replicated for water treatment modeling and promotes the application of smart technology in water treatment.

Study on Performance Evaluation of Multifunctional Microgel System

Soft Microgel (SMG) used to enhance oilfield recovery is a kind of aqueous dispersion chemical agent system of microgel particles. It is usually used in medium and low permeability reservoirs and is generally not used for plugging large pores of reservoirs due to the limitation of particle size. To resolve the problem that SMG cannot effectively block large pores of the reservoir, the multi-functional system (SMG-w) can be synthesized by introducing inorganic components into SMG under special conditions. The main physical and chemical properties of SMG-w are carried out in the laboratory. The results of the study show that SMG-w has an excellent resistant ability to temperature and salinity. Besides, it can also decrease the interfacial tension of oil and water. What’s more, it can react with Ca2+ or Mg2+ in formation water from a large number of flocs in the high salinity reservoir, which can enhance physical and chemical properties of SMG-w and make it be applied in deep profile control of high permeability reservoirs with high temperature and high salinity.

In-situ microscopy investigation of floc development during coagulation-flocculation with chemical and natural coagulants

ABSTRACT This study aimed to include in-situ microscopy in the analysis of floc development during coagulation-flocculation for drinking water treatment. To this end, jartest series were carried out for natural and synthetic waters using aluminum sulfate, sulfate chloride, ferric chloride, and Opuntia sp. as coagulants. Coagulation under optimized conditions was monitored by an in-situ microscope in conjunction with image analysis. Obtained results enabled some insights on the coagulation process. Images captured different stages of initial floc development, including flocs exhibiting heterogeneous, branched, and irregular surface structures. From image analysis, wide distributions of flocculated particle sizes were found for both natural (19–15834 μm) and synthetic water (19–21607 μm), suggesting the occurrence collisions by adhesion and transport between particles, thus influencing floc formation rates depending on the medium. Average size and number of flocs, as determined by the image analysis algorithm as a function of the time, showed inverse correlation of floc growth with water clarification. The microscopic images also illustrated how different coagulants in different water sources undergo breaking through fragmentation or erosion. Our findings also highlight the importance of investigating additional aspects that involve conditions of mixing, development, breaking, regrouping, and resistance of flocs.

Rheological evaluation of nano-metakaolin cement pastes based on the water film thickness

The aim of this study was to evaluate the rheology of nano-metakaolin (NMK) cement pastes based on the water film thickness (WFT). The effects of the NMK content, water-to-binder (w/b) ratio, superplasticizer (SP), environmental temperature, and hydration time were considered in the rheological test. The fluidity, apparent viscosity, yield stress, plastic viscosity, packing density, and WFT of the investigated NMK cement pastes were determined. The flocculation structures (flocs) of the NMK cement pastes were examined. A mathematical model and a BP neural network model were established to predict rheological parameters. The results showed that the NMK increased the apparent viscosity, yield stress, and plastic viscosity of fresh cement pastes. NMK weakened the effects of environmental temperature and hydration time on the rheology of fresh cement pastes. The NMK addition increased the number of flocs in fresh cement pastes and yielded a lower packing density and WFT. A mathematical model and a BP neural network model based on WFT were available to accurately predict the rheological parameters.

Analysis of flocculation in a jet clarifier. Part 2 - Analysis of aggregate size distribution versus Camp number

Among the various existing technologies for water treatment, the jet clarifier is considered as an effective and compact system as it couples flocculation and clarification in a single unit. In this work, a quasi-two-dimensional apparatus was designed to visualise the interaction between floc size distribution and hydrodynamics in the flocculation zone of a jet clarifier. Measurements of the number of flocs and their size distributions are performed by means of shadowgraphy method and image analysis. Thanks to a coupling between population size distributions and results on local hydrodynamics, the evolution of the number of aggregates along the jet is directly correlated to the recirculation loop present in the flocculation zone. The relative independence of the floc size distributions on the flow rate is discussed in light of the Camp number Gt which remains constant for different flow rates investigated and can thus explain the efficiency of the jet clarifier in terms of flocculation.

Investigation of a novel enhanced stabilized foam: Nano-graphite stabilized foam

To solve the problem of poor stability of ordinary foam in high-temperature conditions, nano-graphite (NG) was used in this study as a foam stabilizer to enhance stability. First, the foam was statically evaluated by the stirring method, and the influence of surfactants, NG, and temperature on foamability and stability were evaluated. Then, the surface tension, apparent viscosity, micromorphology, and contact angle of the foam were measured using a rheometer, microscope, and contact angle measuring instrument. Finally, the plugging ability of the foam was evaluated through a water flooding experiment. The results showed that the synergistic effects of nano-graphite and surfactant significantly improved foam stability, and the best surfactant and nano-graphite concentrations were determined. Compared with ordinary foam, NG-stabilized foam had better stability with increasing temperature. Using the apparent viscosity, surface tension, micromorphology, and contact angle, the mechanism of nano-graphite stabilization of foam was explained: the mixture of NG and surfactant formed a small number of flocs, which increased the apparent viscosity of the foam. Nanoparticles were adsorbed on the gas–liquid interface, which increased the thickness of the liquid film, improved the mechanical strength of the liquid film, and delayed the drainage of the liquid film and the coalescence of bubbles, thereby improving the stability of the foam. After injecting foam, the pressure difference generated by NG-stabilized foam was approximately twice that of ordinary foam, showing stronger plugging ability.

Optimal floc structure for effective dewatering of polymer treated oil sands tailings

Synthetic polymeric flocculants such as anionic polyacrylamides are widely used for dewatering mature fine tailings (MFT) generated from oil sands mining operations. Many studies have investigated the effects of polymer properties on dewatering efficiency. However, only a few studies have investigated the reasons for effective dewatering at optimum dosages from the perspective of understanding changes in the internal and external microstructure of the floc. In MFT, clay solids are dispersed in brine (along with trace amounts of bitumen) and are known to have a house-of-card like microstructural arrangement due to electrostatic stabilization. In this study, we investigated why there is maximum dewatering in the specific polyacrylamide (PAM) polymer-MFT system at optimum dosage. To understand this, we investigated the morphological changes in the house-of-cards microstructure in terms of porosity and floc density when flocculated at different polymer dosages as well as the corresponding floc strength, size, and re-flocculation tendencies. SEM imaging results showed that at the optimum dosage of 1000 ppm the internal floc microstructure had two different characteristic zones of reduced porosity and open channels, respectively, indicating that this arrangement could have led to an effective squeeze-out of water from the pores. Focused Beam Reflectance Microscopy results indicated that optimum dosage leads to effective dewatering due to flocs formed in the size range of 10–50 μm and 50–150 μm having reduced re-flocculation tendencies. Optimum dosage resulted in the least number of flocs and the reduction of flocs in the size range of 10–50 μm and < 10 μm was maximum while the corresponding increase of flocs in the size range of 50–150 μm was maximum as compared to other dosages. Additionally, the flocs at optimum dosage did not change in number for a given size range of flocs even after 1-hour stirring indicating strong floc formation. These observations are specific for the particular pairing and could form a basis for investigating other polymer-tailing systems.

Change of sandstone microstructure and mineral transformation nearby UCG channel

In order to study the evolution law of surrounding rock microstructure of underground coal gasification, and to reveal the principle from the change of mineral composition and organics in rock, the sandstone nearby the gas transmission channel was used as the tested rock. In this paper, the rock was heated at 300, 400, and 500 °C, simulating the heat convective environment of the gas transmission channel. The mineral, organic functional groups, and microstructure of sandstone transformation products were detected by XRD, FTIR, and SEM. It is concluded that the kaolin in the sandstone gradually transforms into metakaolin with the increase of temperature, meanwhile the carboxyl group and the oxygenic functional group decrease. The generation of metakaolin and the precipitation of organics increase the number of fractures in samples, which is the main reason for the compressive strength and elastic modulus for the sandstone decreases with increasing temperature for temperatures greater than 500 °C. The microscopic manifestation is the appearance of a large number of flocs on the surface. Macroscopically, the exterior appears as a grayish shell. The flow resistance and the adsorption property are weakened, and the permeability is enhanced.

Characterization of Filamentous Flocs to Predict Sedimentation Parameters Using Image Analysis

In wastewater treatment plants, the degradation of complex substances that contaminate water is carried out by microorganisms, which are fixed by a network formed by filamentous bacteria, creating large flocs that settle easily. However, the excessive growth of said bacteria causes a series of drawbacks such as the reduction of settling velocity, leakage of activated sludge with the effluent, and formation of supernatant, a phenomenon known as bulking. This research work seeks to develop and evaluate a procedure for the physical characterization of the flocs to determine the parameters that affect the settling velocity and thereby detect and control bulking. For this purpose, sedimentation and image analysis tests were carried out from wastewater from the Aguas Antofagasta treatment plant (Chile). The image analysis was performed with images captured from an optical microscope in two magnifications (100x and 50x), which were analyzed by marking each floc individually and characterized by an image processing software. Additionally, sedimentation tests were performed on columns (area of 74 (cm2) and height of 70 (cm)). As a result, an inversely proportional dependence was found on the settling velocity evaluated by the Vesilind equation in the zone of constant fall velocity with respect to the number of flocs connected per cluster, giving an estimate of the settling velocity depending on the number of flocs connected. This would allow predicting settling velocity with image analysis, taking into account that the problem of bulking is determined by the type of filamentous bacteria that causes it and the sedimentation process is affected in large part by local factors. It can be concluded through this study that as the number of flocs connected per cluster increases, the settling velocity decreases. This study provides wastewater treatment plants with a practical tool to determine sedimentation times and thus improve the quality of the treated water, avoiding problems of flocs leaking with the effluent. In addition, the image analysis itself allows rapid detection of the phenomenon of bulking and its severity.

Cationic xylan- (2-methacryloyloxyethyl trimethyl ammonium chloride) polymer as a flocculant for pulping wastewater

In this work, pulp mill wastewater was treated with a novel polymer flocculant, which was synthesized through polymerizing (2-methacryloyloxyethyl) trimethyl ammonium chloride (DMC) and xylan. Xylan-DMC polymer removed 94.5% of turbidity, 61.7% of chemical oxygen demand (COD), 45.0% of lignin, 65.7% of sugar and 73.5% of biological oxygen demand (BOD) from the wastewater at the polymer concentration of 500 mg/L. The flocculation mechanism was fundamentally assessed with determining hydrodynamic size and chord length of flocs in the wastewater at different dosages of xylan-DMC polymer in the system. By adding polymers, the number of flocs with a small chord length (10–50 μm) decreased, while that with a large chord length (150–300 μm) increased, indicating the small particles agglomerated via bridging induced by the polymer. The sedimentation of formed flocs was quantitatively investigated by a vertical scan analyzer and the results depicted that the flocs could settle readily from the system.

Effects of C/N ratio on nitrate removal and floc morphology of autohydrogenotrophic bacteria in a nitrate-containing wastewater treatment process

The effects of C/N ratio of a nitrate-containing wastewater on nitrate removal performed by autohydrogenotrophic bacteria as well as on the morphological parameters of floc such as floc morphology, floc number distribution, mean particle size (MPS), aspect ratio and transparency were examined in this study. The results showed that the nitrate reduction rate increased with increasing C/N ratio from 0.5 to 10 and that the nitrogen removal of up to 95% was found at the C/N ratios of higher than 5 (between 0.5–10). Besides, high C/N ratio values reflected a corresponding high nitrite accumulation after 12-hr operation, and a fast decreasing rate of nitrite in the rest of operational time. The final pH values increased with the C/N ratio increasing from 0.5 to 2.5, but decreased with the C/N ratio increasing from 2.5 to 10. There were no significant changes in floc morphology with the MPSs ranging from 35 to 40μm. Small and medium-sized flocs were dominant in the sludge suspension, and the number of flocs increased with the increasing C/N ratios. Furthermore, the highest apparent frequency of 10% was observed at aspect ratios of 0.5 and 0.6, while the transparency of flocs changed from 0.1 to 0.7.

플럭크기를 이용한 응집공정 진단에 관한 연구

An assessment of flocculation was performed by measuring the distribution of the floc size during sedimentation in water works. The size and number of flocs have a greater effect on an evaluation of the efficiency of flocculation rather than the turbidity. The data was collected in situ using particle image velocimetry and image analysis. The measurements were carried out at a water depth of 1m. The removal efficiency of the total organic compounds, UV absorbance and turbidity depended on the size and floc size distribution in flocculation as the G value. The G value of 50 sec-1, 30 sec-1 and 10 sec-1 showed the highest degree of efficiency in the case of an inlet water turbidity of 5 NTU, and the highest degree of efficiency was observed at a G value of 65 sec-1, 40 sec-1 and 10 sec-1 when the inlet water turbidity was 263 NTU. The number of flocs with a distribution of above 1,200㎛ was 14. The dynamics between two important growth mechanisms were investigated as the energy input changed. This is a certain method that makes use of the size and number of flocs as an efficiency assessment.

선회류를 이용한 응집침전모듈의 개발 및 실증 연구

본 연구의 목적은 소규모 응집침전모듈의 개발 및 lab-scale 테스트를 통한 실증이다. 최근 하수처리율이 높아짐에 따라 비점오염원 관리에 대한 관심이 높아지고 있어 소규모 처리장치 개발의 필요성이 증대되고 있다. 본 연구의 응집침전모듈은 응집공정 이후 외부 영역에서 선회류를 통한 플럭(floc)의 추가 성장 및 미세 플럭 수의 감소, 내부 침전 영역에서 수직 수평류 복합침전방식을 통한 침전효율 증대로 효과적인 고액분리가 가능토록 하였다. 응집침전모듈은 수직 수평류 복합침전 방식을 통해 재래식침전조에 비해 같은 체적에서 침전면적 및 표면부하율을 4.4배 증가시킬 수 있었다. 본 연구에서 외부 및 내부 침전 영역에서의 선회류 형성 유지와 내부 침전영역에서의 균등한 유량분배를 본 공정의 중요한 설계인자로 선정하였고, 이의 도출을 위해 유체유동해석 모델인 FLUENT를 이용하였다. 선회류 유동경향 모사를 통해 유입속도, 외부조의 규격, 하부콘호퍼 깊이 등을 결정하였고 속도분포 및 유량분배 해석을 통해 유출공 직경과 개수, 유출홀 직경 등 내부 침전영역의 세부 규격을 도출하였다. <TEX>$60{\ell}/hr$</TEX>규모의 파일럿 테스트 결과 20분의 체류시간 동안(표면부하율은 <TEX>$37.3m^3/m^2$</TEX>일)탁도 300~800 NTU의 폐수를 고분자응집제 주입 없이 10 NTU 이하로 처리할 수 있었으며, 유체유동해석 모델을 활용한 설계인자 도출의 가능성을 확인하였다. The purpose of this study is small scale coagulation module is developed and demonstrated through a lab-scale test. Recent as a sewage treatment rate increases, have heightened the interest in the necessity on the nonpoint source and developing a small processing unit has been increased. Coagulation sedimentation module in this study is additional growth of floc through swirling in the outside zone, reduction of microstructure floc number and the internal settling zone through vertical/level flow complex sedimentation method after the coagulation process precipitation method as an effective high separation efficiency can be divided was also assessed. Coagulation sedimentation module can increase the load factor was 4.4 times compared to conventional clarifier base on the same volume and surface area through vertical/level flow. In this study, this process was selected formation and maintenance of swirling and uniform flow distribution in the internal settling zone as an important design factor, to derive its FLUENT was used to characteristics of the flow model. Through the simulation of swirling, influent velocity, dimensions of external basin, hopper depth of bottom cone was determined and through analysis of velocity distribution, flow distribution detailed specifications are derived like as diameter and number of effluent hole. Lab-scale(<TEX>$120{\ell}/hr$</TEX>) test results, influent of 300~800 NTU to less than 10 NTU without polymer feeding was able to operate in the 20minutes retention time(surface loading rate <TEX>$37.3m^3/m^2$</TEX>-day), and through analysis FLUENT the possibility of using design parameters were derived.

Influence of cycles of high and low turbulent shear on the growth rate and equilibrium size of mud flocs

Abstract Effects of repeated exposure to multiple cycles of high and low turbulent shear on mud floc growth pattern and equilibrium size were investigated through a laboratory study. The specific research questions examined were: (1) do repeated cycles of floc growth and breakup change the equilibrium floc size from one cycle to the next?; and (2) do these repeated cycles impact the floc growth rate and path to equilibrium? For the experiments, a 50 mg/l mixture of kaolinite and montmorillonite clay was sonicated and introduced to a mixing chamber to allow for flocculation under a mean turbulent shear rate of G = 35 s− 1. Floc size time series, floc circularity index, and time series of the number of flocs were measured using a camera system and image processing routines. After the flocs reached an equilibrium size, the floc suspension was broken down with vigorous turbulent mixing (G = 400 s− 1) for 15 h. Flocs were then allowed to regrow at a shear rate of G = 35 s− 1. This procedure was repeated seven consecutive times. The data show that the different initial particle size distributions after sonication and after intense shearing had almost no effect on the equilibrium floc size, but that difference in initial size did significantly impact the floc growth pattern before the equilibrium was reached. With each repeated floc breakup and growth cycle, the rate of floc growth decreased. Each of the seven regrowth cycles was modeled with the Winterwerp (1998) equation for the mean floc size by calibrating the collision and breakup efficiency coefficients for each cycle. To obtain a good fit to the data, both the collision and breakup efficiency coefficients had to be reduced with each successive cycle. The observations and modeling results suggest that flocs become slightly stronger and less reactive with each repeated cycle of growth and breakup. The consistency of the equilibrium floc size in the experiment suggest that given enough time, floc settling velocity maybe reasonably modeled as a function of local conditions. However, if the time it takes to reach equilibrium is larger than the time scale of the flow of interest, then the floc settling velocity may be difficult to define without knowledge of the turbulent shear conditions encountered prior to the point of analysis; even when using a size evolving floc modeling approach.

A Research on the Morphology and Composition of Flocs (Part 1: Floc Breaage Disregarded)

The characteristics of flocs aggregated in flocculation have been paid more and more attention for a long time. In this paper, a new classification and analyses method dealing with the flocs is developed. The flocs formed after flocculation is divided into four kinds, including the left primary particles, linear flocs with all component particles in a line, planar flocs with all component particles on a plane and volumetric flocs with all component particles in a three-dimensional space. By analyzing the formation approaches of different kind of flocs regardless of the floc breakage, the number of every kind of floc is analyzed to be related with the suspension concentration mathematically. After comparing the different items in the models describing the relationship of floc number and concentration, a series of simplified expressions are presented. Lastly, a mathematical equation relating the measurable suspension viscosity with the numbers of different flocs is obtained.

Floc growth kinetics in magnesium hydroxide coagulation process

The population balance modeling (PBM) had been applied to simulate the floc growth with time in magnesium hydroxide coagulation process. Floc number and size distribution were investigated to evaluate the kinetics in a continuous steady experiment. The floc grows fast in rapid mixer and very slow in flocculation basin and sedimentation tank. The experimental data agreed well with the size-dependent model, and the floc formation and growth empirical function was also obtained to understand the relationship between floc formation rate and growth rate under different stages of coagulation. It was also found that floc growth rate increased with the increase of floc size. Although the floc counts in the range of 2–5μm accounting for about 90%, the setting characteristics of kaolin colloidal suspensions presents good and the turbidity removal efficiency can reach 98%.

Sizing and counting of saccharomyces cerevisiae floc populations by image analysis, using an automatically calculated threshold

A standardized image analysis method has been developed permitting determination of the number of yeast flocs and their size distribution. The method includes image grabbing, image enhancement, automatic determination of the appropriate threshold, curve fitting of the areahistogram, determination of the mean single floc area and its standard deviation, and floc counting. The extension of the method to other applications is immediate and straightforward. Two Saccharomyces cerevisiae floc Populations (with ages of 48 and 72 h) were analyzed. The results showed a variation around the mean of 9%-12% for the single floc mean area, 6%-7% for the number of single flocs, and 5%-6% for the total number of flocs. Aggregates of two flocs (doublets) and three flocs (triplets) were enumerated. The correctness of the method was checked by analyzing the parameters of interest as a function of the threshold. The constant correlation between the parameters and the threshold showed the validity and consistency of the method. (c) 1996 John Wiley & Sons, Inc.

Relations between the aspect ratio of carbon nanotubes and the formation of percolation networks in biodegradable polylactide/carbon nanotube composites

AbstractThe biodegradable polylactide composites containing carbon nanotubes (CNTs) with high aspect ratio (HAR) and low aspect ratio (LAR) were prepared by melt mixing. The physical properties of those two systems were characterized in terms of rheology, conductivity, and mechanical properties for establishing preliminary structure–property relations. Several viscoelastic models were then used to further describe the relations between aspect ratio and percolation network of CNTs. The results show that these two CNTs present different structural characteristics in the polylactide (PLA) matrix during melt mixing: the LAR CNTs are far stiffer than the HAR CNTs. At low loading levels, the former is dispersed as bent fibers or their small bundles, whereas the latter is dispersed as self‐entangled flocs, presenting far larger hydrodynamic radius than the former. At high loading levels, both are dispersed as flocs due to strong tube–tube interactions. However, the two CNTs show approximate average floc size and mesh size because they present same rigid length and effective aspect ratio. At identical loadings, therefore, the HAR CNTs have more total number of flocs than that of the LAR CNTs, forming network with more compact structure and imparting higher contributions to properties of the composites as a result. © 2010 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 48: 479–489, 2010