Rate Of Polycondensation Research Articles

Applying pH Modulation to Improve the Thermal Stability of Melamine-Formaldehyde Microcapsules Containing Butyl Stearate as a Phase-Change Material.

This paper presents a two-stage microencapsulation process that uses pH modulation to enhance the thermal stability of microcapsules that consist of a melamine-formaldehyde (MF) shell and a butyl stearate core. In the first stage, the pH value was modulated between 6.0 and 8.0. Rising the pH value to 8.0 slowed the polycondensation rate, allowing the MF resin with a lower degree of polymerization to migrate to the capsule surface and form a smooth shell. Lowering the pH value to 6.0 accelerated polycondensation. In the second stage, a relatively fast, continuous reduction in the pH value to 5.0 led to further MF polycondensation, hardening the shell. Post-curing at 100 °C prevented shell damage caused by the liquid-gas phase transition of the core material during the process. The microcapsules produced by increasing the pH value to 8.0 twice demonstrated improved thermal stability, with only a minimal overall weight loss of 5% at 300 °C. Significant weight loss was observed between 350 and 400 °C, temperatures at which the methylene bridges in the MF shell undergo thermal degradation. The results from differential scanning calorimetry, electron microscopy, and thermogravimetry analyses confirmed a successful optimization of the microencapsulation, showing that these microcapsules are promising for thermal energy storage and other applications that require high thermal stability.

Geopolymerization of Coal Gangue via Alkali-Activation: Dependence of Mechanical Properties on Alkali Activators

Coal gangue (CG) is a residual product from coal mining and washing processes. The reutilization of CG to produce geopolymers is a low-carbon disposal strategy for this material. In this study, the calcined CG (CG700°C) was used as aluminosilicate precursors, and the effects of alkali activators (i.e., Na2SiO3/NaOH, NaOH concentration, and liquid–solid) on the mechanical characteristics and microstructure of CG700°C-based geopolymers were investigated. The findings indicated that the specimens with a liquid–solid ratio of 0.50 (G2.0-10-0.50) exhibited a compact microstructure and attained a compressive strength of 24.75 MPa. Moreover, increasing the Na2SiO3/NaOH mass ratio has shortened the setting times and facilitated geopolymer gel formation, resulting in a denser microstructure and improved compressive strength. The higher NaOH concentrations of alkali activators facilitated the dissolution of CG700°C particles, and the geopolymerization process was more dependent on the condensation of SiO4 and AlO4 ions, which promoted the formation of geopolymer networks. Conversely, an increase in the liquid–solid ratio from 0.50 to 0.65 had a negative impact on compressive strength enhancement, impeding the polycondensation rate. Examination through scanning electron microscopy and mercury intrusion porosimetry revealed that employing a lower Na2SiO3/NaOH mass ratio (G1.2-10-0.55), smaller NaOH concentrations (G2.0-8-0.55), and a higher liquid–solid ratio (G2.0-10-0.65) led to the presence of larger pores, resulting in decreased 28 days compressive strength values (15.87 MPa, 13.25 MPa, and 14.92 MPa, respectively), and a less compact structure. The results suggest that the performance of CG700°C-based geopolymers is significantly influenced by alkali activators.

Synthesis of flexible, strong, and lightweight oxide ceramic nanofibers via direct electrospinning of inorganic sol for thermal insulation

Oxide ceramic nanofibers are widely used in aerospace and civil facilities due to their superior thermal stability and fire resistance. Currently, electrospinning, one of the important methods for preparing oxide ceramic nanofibers, must rely on adding organic polymers to impart spinnability to inorganic sols. However, these organic polymers will inevitably leave hole flaws in the ceramic nanofibers due to thermal decomposition during the subsequent ceramization process, seriously damaging their mechanical properties. Here, a direct electrospinning strategy for inorganic sol through hydrolyzation–polycondensation rate modulation is proposed, which gets rid of the dependence of spinnability of inorganic sol on organic polymer. Taking silica nanofibers as an example, it exhibits excellent flexibility and mechanical strength (tensile stress up to 1.4 MPa), as well as thermal insulation properties (thermal conductivity as low as 0.0551 W m−1 K−1 at 300 °C). This work provides new insights into developing other high–performance oxide ceramic materials.

Single-Crystalline Hydrogen-Bonded Crosslinked Organic Frameworks and Their Dynamic Guest Sorption

ConspectusPorous organic framework materials constructed by periodically aligned molecular entities offer chemically tailored microenvironments to absorb molecules and ions for various applications. Fundamentally understanding the microenvironments of these porous organic materials─from pore size, shape, and dynamics to potential substrate binding sites─is critical for the rational design of porous organic materials. The solid-state structures of these porous organic materials, such as covalent organic frameworks (COFs), can provide unambiguous atomic-level structural details. However, it remains challenging to synthesize these materials as single crystals that can be fully characterized by single-crystal X-ray diffraction (SCXRD) or rotational electron diffraction (RED) analysis. In addition, the balance of single crystallinity, permanent porosity, and good chemical stability requires delicate control of the assembly of the molecular building blocks and covalent crosslinking during synthesis. In this Account, we discuss the development of hydrogen-bonded crosslinked organic frameworks (HCOFs) possessing balanced single crystallinity and high chemical stability. HCOFs are obtained through covalently crosslinking molecular crystals that are preorganized via hydrogen bonding. Due to the dual hydrogen-bonded network and covalent crosslinking, HCOFs can deform upon guest adsorption by breaking the hydrogen bonds and subsequently restore their original form through the desorption of guests by re-establishing the hydrogen-bonded networks. Thus, HCOFs can dynamically adjust their pore sizes according to the framework–substrate interactions. In the discussion, we link HCOFs with COFs and single-crystalline 2D polymers by comparing their synthetic approaches to accessing high crystallinity. The method to synthesize HCOFs allows for the employment of various flexible building blocks and linking motifs that are largely avoided in the current design regimes of COFs and 2D polymers. We also draw the connections between HCOFs and hydrogen-bonded organic frameworks (HOFs) by highlighting their shared design principles for constructing hydrogen-bonding networks with large voids. Compared to their hydrogen-bonded precursor crystals, reinforcing the hydrogen-bonded networks with covalent linkages endows HCOFs with enhanced chemical and structural stability. In addition, we emphasize that the structure elucidation of HCOFs often requires combined SCXRD analysis and experimental evidence, with the methods and challenges thoroughly discussed. The details are presented in the following sequence: (1) synthesizing single-crystalline COFs by matching the polycondensation rate to the nucleation rate and their subsequent analyses by SCXRD/RED; (2) obtaining single-crystalline polymers and networks through topochemical reactions; (3) constructing HOFs with designed voids using highly directional hydrogen bonding building blocks; and (4) developing HCOFs via monomer crystal engineering followed by single-crystal to single-crystal (SCSC) synthesis and studying their unique dynamic guest sorption behaviors. We hope this Account will inspire researchers to expand the synthetic methods for advancing HCOFs with detailed solid-state structures, as well as designing porous organic framework materials with dynamic sorption capabilities to enhance their performance for applications in molecular storage, separation, catalysis, etc.

Измельченные бумажно-смоляные пленки как реакционно-способные наполнители карбамидоформальдегидных смол

Powdered paper-resin films (PRF) composed of melamine-urea-formaldehyde resin and bleached pulp seem to be promising fillers for plywood glues as they increase the viscosity of the glue composition and interact chemically with the components of ureaformaldehyde resins. It is generally accepted that when 4–6 % PRF is mixed with ureaformaldehyde resin, the viscosity of the glue increases by 80–110 %, however the increase in viscosity is followed by an increase in the gelatinization time of the glue by 25–35 %. The reactivity of the films defined by the polycondensation rate of urea- and melamine-ureaformaldehyde oligomers was studied by determining the residual hydroxymethyl groups in the cured adhesive compositions. Our results show that when we add PRF into the resin, the content of unreacted hydroxymethyl groups increases from 1.0 % of a composition without any fillers to 2.5 % of a composition with 10 % of films in it. We found that the content of unreacted hydroxymethyl groups in the cured glue depends on the gelatinization time of the glue composition by 90 %. To speed up the glue curing, we replaced the ammonium chloride with a more effective curing agent МО-4СБ (Russian abbreviation), which helps to reduce the time of gelatinization time by 15 % for a mass fraction of 4–5 %. The content of hydroxymethyl groups in the cured glue with 4 % of PRF and 4–5 % of МО-4СБ was 0.6–0.7 %, which is 30–40 % less than in the resin without fillers. Samples of 3-layer plywood that contain 4 % of filler and 4 % of modifier-curing agent МО-4СБ had a glued seam that was 5 % stronger that of a control plywood sample which consisted of 8 % of kaolin and 1% of ammonium chloride. The increase in strength has reduced the rate of glue consumption by 15 % while meeting the requirements of the State Standard GOST 3916.1–2018 for the physical and mechanical parameters. As a result, using 4 % PRF as a filler for glue made from urea-formaldehyde resin helps to increase the viscosity of the glue on par with other mineral fillers. In addition, it increases the strength and the water resistance of the cured polymer. The growth of the physical and mechanical parameters occurs due to the polycondensation of urea- and melamine-urea-formaldehyde oligomers. However, an acceptable reaction rate requires the use of more effective curing agents than ammonium chloride.

Study of the open porosity of carbon materials using thermoporometry

Thermoporometry is a calorimetric method for characterizing pore structure from the melting or freezing point depression of a liquid confined in a pore, by the reason of the added contribution of surface curvature to the phase-transition free energy. Porous materials are widely used in the production of noise and vibration-absorbing coatings, thermal insulation, filters, etc. We present the results of studying the porous structure using thermoporometry, a method based on lowering the melting point of the working substance (penetrant) which previously filled micro- and mesopores of the sample under study. The open porosity of carbon materials based on phenol-formaldehyde resins and a pore former obtained after pyrolysis under different conditions of microphase separation induced by polymerization is analyzed. The tests were carried out using a differential scanning calorimeter. Bidistilled water, which has a relatively high value of the enthalpy change upon melting of the crystalline phase is used as a penetrant to lower the error of measurements. Differential and integral curves of the size distribution of micro- and mesopores are presented. It is shown that an increase in the microphase separation temperature entails an increase in the total porosity. Moreover, an increase in the polymerization rate of phenol-formaldehyde resin due to resin modification with m-cresol also facilitated an increase in the cumulative volume of micro- and mesopores. It is shown that replacement of phenol with paracresol leads to an increase in the total porosity even under a significant decrease in resole resin polycondensation rate. The results obtained can be used in the development of carbon matrices with controlled parameters of the mass transfer.

Parameter Estimation in a PO3G Model with Temperature Effects

AbstractA comprehensive dataset containing 1779 measured values, collected from seven experimental runs, is used for parameter estimation in a model for batch polycondensation of biobased 1,3‐propanediol. The data are from dynamic experiments conducted between 160 and 180 °C using a super‐acid catalyst with concentrations between 0.1 and 0.25 wt%. The model accounts for generation, consumption, and evaporation of linear and cyclic oligomers, the inhibitory influence of water on the rate of polycondensation, and the dynamic behavior of an overhead condenser. In total, the model contains 70 kinetic, transport, and thermodynamic parameters. A mean‐squared‐error criterion reveals that the influence of temperature on mass‐transfer coefficients is significant. The model provides a good fit to the data and also gives reliable predictions of validation data that are not used in parameter estimation. Typical deviations between model predictions and data are within 1.75% of average measured values for linear and cyclic oligomers.

Effect of Particle Size of Quartz Sand Filler on Microstructure and Strength of Alkali-Activated Slag-Based Materials

Interaction between quartz sand and water glass has been investigated and characterized by using the Si/Na molar ratio to determine the role of silica in the polycondensation rate and mechanical properties of the synthesized materials as a function of quartz sand particle size. Results of atomic emission spectroscopy, SEM and compressive strength tests show that interactions between sodium silicate solution and quartz sand depend on the degree of dispersibility that determines the degree of amorphization of quartz sand. When using ordinary quartz sand sodium silicate solution acts as a thin layer of glue covering the grains of sand and weakly binds them to each other, while using finely ground quartz sand in the mixture there is a dissolution–precipitation reaction that modifies the surface layers of the particles and more strongly consolidating the granular system. The increase in the molar ratio of Si/Na in sodium silicate solution containing finely ground quartz sand occurs due to the increase in the proportion of amorphous quartz (according to XRD) and corresponds to the described mechanism. Then, samples of alkali-activated slag-based materials with a coarse ordinary quartz sand and finely ground quartz sand were synthesized, compared in terms of strength and the latter characterized by SEM, porosimetry, XRD. The increase of dispersibility and amorphization of quartz sand is established to favors to form consolidated of low-temperature curing materials based on alkali-activated slag and quartz sand with the significantly increased compressive strength from 30–44 MPa for mixtures based on ordinary coarse quartz sand to 95–140 MPa for finely ground slag/sand blended mixture.

SrZr0.9Y0.1O3−δ thin films by in-situ synthesis of triple alkoxide for protonic ceramic electrolyser membranes

Synthesis of the proton-conducting electrolyte SrZr0.9Y0.1O3−δ(SZY) was undertaken by the sol–gel method employing an all-alkoxide route from reaction of strontium alkoxide produced in-situ and commercial zirconium and yttrium alkoxides. The solution was homogenized by a previous ligand exchange in 2-methoxyethanol to control the polycondensation rate and achieve SZY at the low final firing temperature of 700–800 °C. SZY thin films (~270 nm) were assisted by dip-coating on different substrates and characterized by scanning and transmission electron microscopy, grazing X-ray diffraction and confocal micro-Raman spectroscopy, revealing well-crystallized SZY phase with orthorhombic symmetry (space group, Pnma). Impedance spectroscopy of a thin film deposited on a quartz substrate revealed that protons contribute to transport in wet conditions as confirmed by a lower conductivity in D2O-humidified air (1.02 eV) compared to H2O-wetted air (0.99 eV), with the difference in activation energy consistent with a conductive isotope effect.

Hierarchically porous monoliths based on low-valence transition metal (Cu, Co, Mn) oxides: gelation and phase separation.

Hierarchically porous monoliths based on copper (Cu), cobalt (Co) and manganese (Mn) oxides with three-dimensionally (3D) interconnected macropores and open nanopores were prepared using metal bromides as precursors via a sol–gel process accompanied by phase separation. The difficulty of gelation for low-valence metal cation was overcome by introducing a highly electronegative Br atom near to the metal atom to control the rates of hydrolysis and polycondensation. The 3D interconnected macropores were obtained using appropriate polymers to induce phase separation. The domain sizes of macropores and skeletons can be controlled by reaction parameters such as concentration and/or average molecular weight of polymers, and the amount of hydrochloric acid. The crystalline metal oxide monoliths with their 3D interconnected macroporous structure preserved were obtained after heat treatment in air.

ДОРОЖНЫЙ БИТУМ С ТЕХНОГЕННЫМ МОДИФИКАТОРОМ

In this work, for the development of oil bitumens, the high-tar oil of the Karazhanbas field, which is economically unprofitable for processing, is used as an additive to the tar of a mixture of oils of Martyshi + Mangystau. As a modifying and plasticizing agent, a technogenic modifier – elemental sulfur (waste from the Tengiz oil and gas processing complex) was used, and various induction moments were introduced, which are an additional source of structure formation of the oxidized feedstock. The Karazhanbas oil field, although economically unprofitable for processing, is unique in its component composition. It contains a large number of high-molecular and resinous-asphaltene components (resins 24,18% and asphaltenes 4,85%) prone toassociative interactions and structure formation. Asphaltenes, in turn, are stabilizers of molecular weight growth, and, in general, make a significant contribution to improving the technological parameters of the target product-bitumen. The mechanism of action of elemental sulfur is that when dispersed with a reaction mixture, there is an increase in the release of acid gases, such as: H2S, CO, SO2, which is explained by an increase in the rates of polycondensation and compaction reactions. This increases the rate of reaction of bitumen sulphurization in the reaction system. Over time, the intensity of gas release decreases due to a gradual decrease in the rates and further cessation of compaction and polycondensation reactions. The structure of the bitumen stabilizes. Induction moments were used as an additional object of the structure builder. The creation of the induction factors increased the amount of reactive monocularity and bicyclogermacrene hydrocarbons (as confirmed by the indicators of instrumental analysis) that accelerate the formation of high molecular compounds, which leads to increased molecular weight of oxidizable starting material, thereby improving the technological parameters of the resulting bitumen. Technogenic sulfur and induction moments in tandem have a combined effect on the physical and mechanical characteristics of the developed bitumen. Summarizing the above results of experimental work, it should be noted that by choosing the calculated amount of raw materials, additives and varying various induction moments, you can get bitumen of the BN 80/120 brand, and this makes it possible to dispose of man-made waste, which is economically and environmentally appropriate.

Reactivity and Aggregative Stability of Colloidal Silica

The properties of colloidal silica taking into account the reactivity of silica, as well as the kinetics of polycondensation and depolymerization, are analyzed. The breaking of siloxane bonds during depolymerization leads to the appearance of reactive Si–OH and Si–O–Me+ groups, destruction of the silica structure, formation of gel-like layers on the surface and in the volume of particles (at a high level of alkalinity), growth of their hydrophilicity, and the dissolution of silica (limiting depolymerization). The formation of gel-like structures is accompanied by an increase in the hydrodynamic radii of the particles, an increase in the viscosity of aggregative stable sols, a decrease in their turbidity upon transition from acidic to alkaline media, sol dilution, and the introduction of electrolytes. Alkalis affect the solid phase depolymerization process by increasing the cation basicity in the series K+ > Na+ > Li+. The formation of gel-like structures causes an increase in the aggregative stability of the sol at pH> 5.5–6.0. Upon reaching pH 9.0–9.5, the quasi-equilibrium of the polycondensation rates and depolymerization reactions ensures the high aggregative stability of the sol. The further increase in alkalinity (increase in pH, silica modulus) in the aqueous phase increases the concentration of depolymerization products and silicate anions containing ionized and non-ionized silanol groups. Under these conditions, the oligo- and polymeric molecules of silicic acids are formed in the aqueous medium during the secondary polycondensation, and, based on them, linear supramolecular structures, the viscosity of the colloidal system grows, and gels are formed.

Dendritic and Core-Shell-Corona Mesoporous Sister Nanospheres from Polymer-Surfactant-Silica Self-Entanglement.

Mesoporous nanospheres are highly regarded for their applications in nanomedicine, optical devices, batteries, nanofiltration, and heterogeneous catalysis. In the last field, the dendritic morphology, which favors molecular diffusion, is a very important morphology known for silica, but not yet for carbon. A one-pot, easy, and scalable co-sol-gel route by using the triphasic resol-surfactant-silica system is shown to yield the topologies of dendritic and core-shell-corona mesoporous sister nanospheres by inner radial phase speciation control on a mass-transfer-limited process, depending on the relative polycondensation rates of the resol polymer and silica phases. The trick was the use of polyolamines with different catalytic activities on each hard phase polycondensation. The self-entanglement of phases is produced at the {O- , S+ , I- } organic-surfactant-inorganic interface. Mono- and biphasic mesoporous sister nanospheres of carbon and/or silica are derivatized from each mother nanospheres and called "syntaxic" because of similar sizes and mirrored morphologies. Comparing these "false twins", or yin and yang mesoporous nanospheres, functionalized by sulfonic groups provides evidence of the superiority of the dendritic topologies and the absence of a shell on the diffusion-controlled catalytic alkylation of m-cresol.

Organosilane film for sand migration control based on in-situ hydrolysis and polycondensation effects

Loosely consolidated or unconsolidated reservoir is susceptible to sand migration that results in rapid production decline and short-lived stimulation enhancement. In this study, water-soluble organosilane used for sand migration control was proposed by considering in-situ hydrolysis and polycondensation effects. A variety of organosilanes were screened by evaluating their hydrolysis and polycondensation rate. The suitable structure of organosilane for sand consolidation was determined. Based on the selected organosilane FX, various factors influencing hydrolysis and condensation rates were studied to determine the usage of organosilane. The result indicates that the rate of hydrolysis and polycondensation dominates the consolidation performance of organosilane by changing the amount of active Si-OH reacting with sand surface. HCl was used to control hydrolysis and polycondensation rate of the organosilane with appropriate formation temperature, operation and shut-in time. The various process control parameters were optimized with the organosilane concentration of 3%–5%, the catalytic HCl concentration of 1%–3%, and formation temperature lower than 100 °C. Static and dynamic sand stabilization experiment showed that the organosilane had a high compressive strength, little loss of permeability, long-term stability against typical formation fluids, and wide compatibilities with various types of acidizing slug. Micro-experiment confirmed the in-situ generation of a hydrophobic film on the touchpoint of sand surface connecting migrated sand with matrix.

Effective binary catalysts of Brønsted acidic ionic liquids and stannous chloride dihydrate for melt polycondensation of l-lactic acid

Sulfonic acid-functionalized task-specific ionic liquids, named as Brønsted acidic ionic liquids (BAILs), stable to water, vacuum and heat, have shown excellent catalysis for esterification. BAILs with imidazolium cation and different anions were reasonably applied as catalysts or cocatalysts of stannous chloride dihydrate (SnCl2·2H2O) for melt polycondensation of l-lactic acid under relatively high vacuum and temperature. Binary catalysts of BAILs and SnCl2·2H2O always presented higher catalytic efficiency compared with the single component. We carefully investigated the influences of acidity and ionic structures of BAILs, amount of catalysts and pressure on polycondensation rate and molecular weight and properties of poly(l-lactic acid) (PLLA). Compared to the traditional binary catalysts of p-toluenesulfonic acid/SnCl2·2H2O, BAILs/SnCl2·2H2O could improve the thermal properties of the products. PLLAs with high molecular weight, good crystallinity, high optical purity and regular stereostructure were synthesized and characterized by GPC, DSC, 13C NMR, XRD and polarimeter.

The study of different additives on a geomaterial reformulated mixture

Geopolymers are new binders resulting from the activation of an aluminosilicate source by an alkaline solution. These ecomaterials are economically and environmentally profitable because they have the advantage of ensuring adhesion between mud bricks and wood. In this context, this paper focuses on the study of the effect of various additives on the kinetic of the setting of geopolymers to facilitate adhesion between various supports. For this purpose, the chemical composition of a laboratory formulation was modified by the addition of aluminous (boehmite) and amorphous silica. Characterization of various mixtures showed that the rate of polycondensation is controllable by the addition of a different aluminosilicate source. Preservation of the working properties of the formed materials was observed. Finally, the addition of a delaying mineral compound allowed the setting time of the geopolymer binder to be adjusted while preserving the mechanical properties.

Recycling of geopolymer waste: Influence on geopolymer formation and mechanical properties

Geopolymers are new binders resulting from the activation of an aluminosilicate source by an alkaline solution. These binders are economically and environmentally profitable since they have the advantage of reusing recycled waste and industrial by-products as aluminosilicate sources. In this context, this paper focuses on the geopolymer wastes incorporation in different formulations and their effect on geopolymer formation and the properties of the final materials. For this purpose, the geopolymer wastes were at first characterized. Three compositions differing in the used alkaline solution and the amount of metakaolin added were investigated. A feasibility study allowed retaining 20% as the waste percentage added or substituted to the metakaolin to still obtain geopolymer materials. Moreover, it was shown that the incorporation of the geopolymer waste may disturb the polycondensation rate which was proven to strongly depend on the solid to liquid ratio and the Si/K ratio of the alkaline solution. Finally, relationships were demonstrated between the compressive strengths and the chemical compositions of the different samples. The low reactivity of geopolymer waste can be compensated with the use of highly reactive alkaline solution or the increase of the amount of metakaolin in the mixture.

Addition of low reactive clay into metakaolin-based geopolymer formulation: Synthesis, existence domains and properties

This paper investigates the addition of low reactive Tunisian clay into metakaolin-based geopolymer as a valorization way in alkaline media. To conduct this investigation, the aluminosilicate precursors used were primarily characterized. Then, several samples were prepared by varying the amounts of metakaolin and clay in the mixture as well as the Si/K molar ratio of the alkaline solution. Correlations between (i) the polycondensation rate of the synthesized mixtures, followed by FTIR spectroscopy; (ii) the working properties, evaluated by the compression test; and (iii) the chemical composition were established, and a model of reactivity was proposed to elucidate the different networks formed for each sample. It appears that the Tunisian clay, after heat treatment, exhibits some reactivity that allows for the formation of consolidated materials. The associated minerals present in the clay seem not to participate in the polycondensation reaction and are simply agglomerated by the alkaline solution. However, the increase of the proportion of metakaolin in the mixture and the depolymerized species in the alkaline solution may improve the polycondensation rate and the working properties of the final materials. The optimal properties were obtained for a mixture of 50% low reactive Tunisian clay and 50% metakaolin and a Si/K ratio of the alkaline solution of 0.50.

Competitive Effects of Stereocomplexation and Hyper‐Conjugation of Triethoxysilyl‐Terminated Poly(d‐lactide) in Poly(l‐lactide) matrices

Triethoxysilyl‐terminated poly(d‐lactide)s (eSi‐PDLA) were successfully prepared by hydrosilylation of allyl‐terminated PDLAs (A‐PDLA‐ac) which were readily prepared by ring‐opening polymerization of d‐lactide and the following terminal protection by acetylation. Their acid‐catalyzed hydrolysis produced hyper‐conjugated PDLAs with terminal silanol coupling. Blend PLLA films containing eSi‐PDLA (Mn = 2.1 kDa) in 5‐25 wt.% were successfully prepared by the solution casting method. The blend films were found to take a nano‐porous or micro‐phase separation structure, being different from that of the blend PLLA films containing trimethoxysilyl‐terminated poly(d‐lactide) (mSi‐PDLA) which exhibited particle distribution structure. This difference was reasonably attributed to the different rate of hydrolytic polycondensation of the trimethoxy‐ and triethoxy‐silyl terminals. These results revealed that the competing sterecomplexation/ hyper‐conjugation/phase separation can afford specific morphologies, allowing fine control of properties.

Strength and microstructural properties of fly ash based geopolymer concrete containing high-calcium and water-absorptive aggregate

In this research, performance of limestone and oil palm shell (OPS) as the alternative aggregates in fly ash based geopolymer concrete was evaluated based on the fresh and hardened concrete test. Fly ash and oil palm shell were studied due to their abundant availability as industrial and agricultural waste. Experimental works were conducted by replacing the portion of coarse and fine aggregate in concrete with limestone and oil palm shell in various percentages. Evaluation of its performance was done based on slump, compressive strength, and porosity test. Microstructure analysis was added via Scanning Electron Microscope (SEM) and Energy Dispersive X-Ray (EDX) test to support the generated hypothesis. From the fresh properties test, the increasing amount of limestone and OPS have shortened the setting time of fresh geopolymer concrete, even though they presented small variations in the slump's height and diameter results. The availability of Calcium Aluminate Silicate Hydrate (C–A–S–H) structure in limestone based specimen and higher polycondensation rate due to optimum water content in OPS based specimens have stimulated the rapid production of geopolymer gel and improved the strength performance of geopolymer concrete in ambient curing condition. Moderate water absorption from OPS fibers and additional dissolution of Al and Si elements due to formation of C–A–S–H gels from limestone inclusion have presented 10% OPS and 25% limestone as the optimum replacement to river sand and coarse granite aggregate, respectively. In ambient curing, 25% limestone presented a 35.23% higher strength while 10% OPS had 11.01% higher strength than control. An escalation to the curing temperature reduced the efficiency of both aggregates, where only 25% limestone was able to produce specimen with 2.34% higher strength than control A supportive analysis from SEM and EDX has also revealed the existence of poly(sialate), poly(sialate-siloxo), poly(sialate-disiloxo) and sialate link in the geopolymer matrix. From this research, the applications of limestone and oil palm shell in geopolymer concrete have presented a nurturing result, particularly as the alternative aggregates in ambient-cured application.