Crystallization Peak Temperature Research Articles

Ultrasound and pulsed electric field treatment effect on the thermal properties, oxidative stability and fatty acid profile of oils extracted from berry seeds

AbstractThe seeds of berry fruits which are considered as a by-product may be valorized by recovering the oil they content. Nevertheless, the conventional extraction methods are time, energy and organic solvents consuming. In order to make extraction more environmental-friendly, alternative methods, like ultrasound-assisted and pulsed electric field-assisted processes, are being developed. The procedure of extraction may however influence the quality of obtained oil. The following study aims to define the effects of ultrasound and pulsed electric field application in the extraction process on the thermal properties, i.e., oxidative stability, melting and cyclic heating/cooling profiles, thermal decomposition characteristics. Additionally, fatty acid profile assessment was included in the study. Seeds of blackberries, blackcurrants, chokeberries, raspberries and redcurrants were used to extract oil. Based on the results, it can be summarized that extraction method influenced the resistance of oils to oxidation. Ultrasound-assisted process resulted in oils with the highest oxidation induction times. Melting profile was slightly influenced by extraction method, with peak temperatures indicating the presence of low-melting and middle-melting triacylglycerol fractions. Differential scanning calorimetry with heat/cool/heat procedure let determine crystallization peak temperatures around − 60 °C, which could be associated with the specific triacylglycerol profile of berry seed oils. The courses of thermogravimetric analysis curves were comparable for all the tested samples. The fatty acid profile study revealed that all the studied thermal properties were affected by the unique fatty acid percentage share, with a great predominance of polyunsaturated fatty acids. Obtained results allowed to conclude that extraction method influenced oxidative stability, thermal properties and fatty acid profile only to some extent. The most promising extraction method among analyzed seems to be ultrasound-assisted extraction as it provided oil with high oxidative stability, typical thermal properties and unchanged fatty acid profile, without being harmful to natural environment due to possible reduction in solvent and time consumption.

Conjugated safflower seed oil and its oleogels stabilization properties: Thermodynamic properties, rheology, oxidative stability

Conjugated safflower seed oil (CSSO) was used as the base oil, and beeswax (BW) was used as the gelling agent to prepare BW-CSSO oleogel. The effects of different additions of wax on the properties of BW-CSSO oleogel, as well as their oxidative stability, were investigated. The results indicated that an oleogel could be formed with CSSO at a BW concentration of 5 wt% at 25 °C, and the oil-holding capacity and hardness of the oleogel increased significantly as the BW concentration increased from 5 wt% to 11 wt%. Differential scanning calorimetry results showed that the peak crystallization and melting temperatures of the oleogel generally increased with the increase of wax addition, and both the crystallization and melting peaks became clearer and sharper. The rheological results indicated that all the samples showed shear-thinning behavior and higher concentrations of BW-CSSO oleogel were more capable of forming robust structures with lower frequency dependence. The free fatty acid release rate from BW-CSSO oleogel decreased with increasing BW concentration because the oleogel was stronger due to the formation of a more robust network, and the network of strong crystals influences the contact between lipase and oil, slowing down the release of oil from the interior of the oleogel structure and affecting the hydrolysis of oil. The network structure of the oleogel could inhibit the generation of CSSO secondary oxidation products and improve the oxidative stability of CSSO. This study provides the relevant parameters of the BW-CSSO oleogel and lays the foundation for subsequent studies.

Identification of percolation threshold of spray‐dried cellulose nanocrystals in homopolymer polypropylene composites

AbstractUnderstanding the percolation threshold is essential for determining the performance of particle‐reinforced polymer composites. Spray‐dried cellulose nanocrystals (SDCNC) of micrometer size reinforced homopolymer polypropylene (HPP) composites at 20, 30, 40, and 50 wt.% were prepared to investigate the percolation threshold of SDCNC particles in HPP. The effect of a compatibilizer (maleic anhydride polypropylene (MAPP)) at 3, 5, and 7 wt.%, on the SDCNC percolation networks and composites performance were also studied. The results indicated that SDCNC particle percolation networks in HPP were established between 30 and40 wt.%. For composites without MAPP, the impact strength significantly increased by up to 23% below the percolation threshold and declined beyond it. The peak crystallization temperature of HPP was steadily increased until 30 wt.% SDCNC particles were added due to the SDCNC saturated nucleation function at the threshold. Introducing MAPP significantly improved tensile strength (58%), tensile strain (61%), flexural strength (45%), and impact strength (91%) compared with the corresponding composites without MAPP, attributed to the enhanced interfacial adhesion between the SDCNC particles and HPP. Water absorption results indicated that adding MAPP changed the SDCNC particle distribution networks within the matrix above the percolation threshold but did not change it below the threshold.

The synthesis of a novel polymer‐type antistatic agent and its effect on the properties of polypropylene

AbstractIn this paper, a novel polymeric antistatic agent, TMQ, with excellent antistatic properties, low cost, and good compatibility with polypropylene (PP), was prepared from isopentenyl polyoxyethylene ether (TPEG), maleic anhydride (MAH) and homemade quaternary ammonium salt (QAS). The structure is characterized using FTIR and 1H NMR. How the addition of TMQ and the molar ratio of TPEG, QAS, and MAH affect the antistatic, mechanical, and crystalline properties of PP are investigated. The results show that as the feed ratio of TPEG, MAH and QAS is TPEG:MAH:QAS = 1:8:8, the modified PP displays the best overall performances. Further exploring finds out when TMQ is added at 15 wt%, the surface resistivity of PP reduces to 6.78 × 109 Ω/sq and the volume resistivity of PP reduces to 7.9 × 109 Ω cm−1, the notched impact strength and melt index improve by 357% and 991%, respectively, while the tensile strength decreases by 38.6% compared with that of pure PP. Besides, the crystal study shows after TMQ is added, the crystallinity of PP reduces, the melt peak temperature remains essentially unchanged, and the crystallization peak temperature increases slightly. The material has excellent antistatic resistance to washing and durability, and the changes in relative humidity have little effect on its antistatic properties.

Thermal Stability, Crystallization, and Melting Behaviours of Iodine Doped Semiconducting Polyethylene Terephthalate (PET) Thin Films

The influence of iodine doping on the thermal stability, degradation kinetics, and the melting and crystallization behaviors of polyethylene terephthalate (PET) films were investigated. Iodine doping was performed by immersing PET films in 0.4 M I2/l toluene. The thermal stability and degradation kinetics of PET and the semi-conducting PET/iodine complex films were studied using the thermogravimetric analysis-derivative thermogravimetric analysis (TGA-DTGA) studies and the differential scanning calorimetry (DSC). It was found that iodine incorporation accelerated the thermal degradation and weight loss through increased chain mobility owing to the imperfections formed by doping. Both pure and doped films exhibited appreciable thermal stability with the peak degradation temperature above 400 °C. DSC thermograms of the pristine PET and the PET/iodine films in the crystallization regions were recorded during the cooling scan and the significant parameters were studied. The peak crystallization temperature of PET increased from 192 to 209 °C after iodination. Doping initiated crystallization at an early stage of cooling with an increase in the rate of crystallization and smaller crystallization half time. Iodine catalyzed crystallization and acted as a nucleating agent. DSC scans were also used to study the melting characteristics of the polymer samples. The peak melting temperature was lower and the absolute crystallinity reduced for the iodine doped PET films.

Optimized growth of LiZnBO3 monoclinic phase in lithium zinc borate glass ceramics for electrode material

Glass-ceramics (GCs) of glass composition 20ZnO.30Li2O.50B2O3 were prepared via controlled heat treatment at hold times of 2h, 4h, 6h and 8h at crystallization peak temperature (846K). The effect of the hold time of heat treatment on the physical, structural, optical, and electrochemical properties was studied. XRD study revealed the formation of a pure LiZnBO3 crystalline phase. FTIR study revealed the transformation of BO4 units to BO3 units with an increase in the time of heat treatment. Optical band gap energy has been estimated from Diffuse Reflectance spectroscopy and, its values range from 3.26eV–3.36eV. Electrochemical properties were studied using Cyclic Voltammetry and compared with parent glass composition. The GC 20ZnO.30Li2O.50B2O3 heat treated for 8h exhibits the highest value of specific capacitance (∼48 mAh/gV) and energy density (∼18 J/g) indicating that it can be used as an electrode material in Li-ion batteries.

Influence of Sb doping on thermal properties and electrical conductivity mechanism of SbxSe50–xSn20Te30 chalcogenide glassy systems

Tunability of thermal, and electrical characteristics of SbxSe50-xSn20Te30 (x = 2, 4, 6, and 8 at. %) bulk glass systems with varying doping concentrations are the major objective of this study. The melt quenching technique has been employed to synthesize the samples. Various thermal parameters have been inspected by using DSC measurements. The effect of Sb addition on the glass transition temperature (Tg), crystallization temperature (Tc), peak crystallization temperature (Tp), and melting temperature (Tm) have been observed from DSC thermograms. The dependence of Tg, Tc, Tp, and Tm on the heating rate has been measured. The thermal analysis is performed under non-isothermal conditions at heating rates of 5, 10, 15, and 20 K/min. The activation energies for the glass transition temperature are estimated by using the Kissinger method and are found to decrease from (211.21-168.85) KJ.mol−1. Thermal stability and glass forming ability for all glassy compositions have been examined in terms of Hruby's parameter. In addition, electrical conductivity mechanisms over vast temperature and frequency ranges are analyzed. The DC conductivity mechanism has been analyzed by deploying Mott and Greaves's variable range hopping model, while the AC conductivity mechanism has been analyzed by deploying the modified correlated barrier hopping model. AC conductivity scaling property has been examined by using the Pan and Ghosh model. The influence of Sb addition has been observed as the DC and AC conductivity increases with the increase of doping concentration.

Impact of aluminum fluoride addition on crystallization, structure and thermal properties of lead borate glasses

The glass composition (70-x)PbO–(30-y)B2O3–(x+y)AlF3, where x and y ranges from 0 to 20 mol%, were prepared using the conventional melt-quenching-annealing technique. The structural and thermal properties of the glasses were comprehensively analyzed using techniques like Differential Thermal Analysis (DTA), Dilatometry, Fourier-Transform Infrared Spectroscopy (FTIR), X-ray Diffraction (XRD), and Scanning Electron Microscopy (SEM). XRD confirmed the amorphous, non-crystalline structure of the glasses. The glass network was found to be composed of structural units such as PbO4, BO4, BO3 and AlO6 using FTIR spectroscopy. FTIR analysis revealed significant structural changes, including the transformation of BO4 to BO3 units and the increase in non-bridging bonds, particularly with higher AlF3 content. DTA was instrumental in determining characteristic temperatures, such as the glass transition, melting, and peak crystallization temperatures, along with glass stability parameters (∆T, Hr, Tgr) for all samples. The study found that the addition of AlF3 led to a decrease in these characteristic temperatures when replacing B2O3, but an increase when replacing PbO. Variations in the density and thermal expansion of the lead borate glass were observed upon the addition of AlF3, decreasing when substituting for PbO and increasing when substituting for B2O3. These findings provide insights into the properties of oxyfluoride glasses, paving the way for future optimization in their composition for varied applications.

Aging processes in dental thermoplastics – Thermoanalytical investigations and effects on Vickers as well as Martens hardness

ObjectiveThe influence of various aging protocols, representing and accelerating influences present in the dental context, on possible changes in the microstructure and mechanical properties of thermoplastics was investigated. In order to minimize the complexity of the systems, first pure polymers and then later the equivalent dental polymeric materials were analyzed. Materials and methodsPure polymers (Poly(methyl methacrylate) – PMMA, Polyoxymethylene homopolymer – POM-H, Polyether ether ketone – PEEK, Nylon 12 – PA12, Polypropylene – PP) were analyzed before as well as after applying different aging protocols relevant to the oral environment (ethanol, thermocycling, alkaline and acidic setting) by differential scanning calorimetry (DSC) and thermogravimetric analysis (TGA). The thermoanalytical parameters used were glass transition temperature (Tg), melting peak and crystallization peak temperature (Tpm, Tpc) and decomposition behavior.In a second step selected commercially available dental products (Telio CAD – PMMAD, Zirlux Acetal – POMD, Juvora Natural Dental Disc – PEEKD) aged by the protocol that previously showed strong effects were examined and additionally tested for changes in their Vickers and Martens hardness by Mann-Whitney-U test. ResultsThe combinations of pure polymers and viable aging protocols analyzed within this study were identified via TGA or DSC as PA12 & thermocycling, POM-H & denture cleanser/lactic acid/ethanol, PP & lactic acid. The dental polymeric materials PMMAD and POMD due to aging in lactic acid showed slight but significantly (p < 0.01) reduced Vickers and partly Martens hardness. PEEK showed the greatest material resistance within this study.

Impacts of substituting magnesium with zinc on crystallization behaviors in an aluminosilicate glass.

A series of zinc-magnesium mixed aluminosilicate glasses with the molar composition (1-r)MgO·rZnO·Al2O3·2.5SiO2, where r = 0.00, 0.25, 0.50, 0.65, 0.75, and 1.00, were fabricated to probe the effects of substitution of magnesium with zinc on crystallization behaviors. Based on the evolution of phase compositions as revealed by calorimetric behaviors and X-ray diffraction patterns, a series of transparent surface crystallized glasses ranging from high transparency for the pure Zn-end member to heavy translucency for the pure Mg-end member were fabricated through heat treatment at the first crystallization peak temperature for 20 min. With the substitution of Mg with Zn, the evolution of morphology unveiled by optical microscopy is ascribed to the alteration of crystal phases formed from the sole metastable Zn-β quartz solid solution to the coexistence of polycrystal phases containing Zn-β quartz solid solution, μ-cordierite, or α-cordierite. These findings are very helpful for optimizing the performance of crystallized aluminosilicate glasses.

Crystallization of poly(lactic acid) nucleated with the sorbitol TBPMN

We report on the crystallization of poly(lactic acid) (PLA) films in the presence of a sorbitol-based nucleating agent; 1,2,3-tridesoxy-4,6:5,7-bis-O-[(4-propylphenyl) methylene]-nonitol (TBPMN). Dispersion of the nucleating agent was performed by solution-mixing and melt-blending. Crystallization behavior was studied by differential scanning calorimetry (DSC). The structure and morphology were characterized by wide-angle X-ray scattering (WAXS), optical imaging, and atomic force microscopy (AFM). A significant impact of the nucleating agent was observed at or above a threshold concentration of 2 wt%, which was assigned to the solubility limit of TBPMN. The degree of crystallinity reached up to 39.6 % with 2 wt% TBPMN. An influence of the dispersion method was observed on the peak temperature of crystallization (Tcp). While Tcp decreased slightly for solution-mixed films, a sigmoidal trend was noted for melt-blended samples. Under isothermal conditions at 100 °C, the crystallization half-time was lowered from 6.5 min to 1.0 min. Avrami analysis pointed to the formation of 2-dimensional or 3-dimensional crystalline domains; WAXS data revealed α- and α'-crystals, depending on the dispersing method. AFM imaging showed a nanosized fibrillar network of the nucleator within the PLA matrix, demonstrating that TBPMN acted as a soluble self-assembly nucleator.

Effect of Surface Properties of Nanoparticles on the Crystallization Behavior of Polypropylene/Polypropylene‐g‐Silica Nanocomposites

AbstractIn order to investigate the effect of surface properties of nanoparticles (NPs) on the crystallization behavior of nanocomposite, three kinds of silica (SiO2) NPs are dispersed in isotactic polypropylene (iPP) matrix by solution blending method. Specifically, the poor compatibility between inorganic bare SiO2 NPs and organic PP matrix triggers the formation of aggregates and induces the fractionated crystallization with two crystallization peaks at higher particle loading (Φ), i.e., main crystallization peak (MCP) and low temperature crystallization peak (LCP, always located at 124.0 °C). Once short PP chains (0.9 × 104 g mol−1) are grafted onto the surface of SiO2 NPs, the nanocomposites with all Φ only exhibit a single MCP which is attributed to the strong interfacial interaction. With the increase of grafting chain length (9 × 104 g mol−1), the more stretched conformation of grafting chains can provide numerous heterogeneous nucleation sites and significantly accelerate the crystallization rate of PP chains near the surface of SiO2 NPs, which lead to the formation of an extra high temperature crystallization peak (HCP, almost kept constant at 133.0 °C). The occurrence of various crystallization peaks implies that the surface properties of nanoparticles play a vital role in the nucleation ability of nanoparticles.

Thermal behavior of gadolinium-silica gels prepared via sol–gel route combined to γ-irradiation process

Gadolinium-silica (Gd-silica) gels were prepared via sol–gel route combined to γ-irradiation (0–30 kGy), starting from Tetra-Ethyl-Orthosilicate (Si(OCH2CH3)4, TEOS) and gadolinium nitrate Gd(NO3).6H2O used as raw materials. The phase transformation and morphology of the gels derived from both precursors were characterized by XRD and TEM analysis. Differential scanning calorimetry (DSC) under non-isothermal conditions was used to determine the crystallization activation energy (E c) at different γ-doses (0, 8, 15, 25 and 30 kGy), using the methods suggested by Kissinger, Moynihan and Ozawa. XRD analysis of the samples calcined up to 1100°C for 2 h reveals the formation of gadolinium silicate (Gd4.67 (SiO4)3O) apatite crystalline phase with the presence of small traces of gadolinium pyrosilicate (Gd2Si2O7), the average particle sizes about 50 nm. TEM observations show spherical Gd-silicate nanoparticles homogeneously dispersed in silica matrix, the mean diameter size is about 40 nm. From DSC analysis, it was observed that the onset crystallization temperature (T x) and peak crystallization temperature (T c) both increase with increasing γ-dose. According to Kissinger, Moynihan and Ozawa models, the crystallization activation energies for Gd-silicate phase formation were found to be 465.2, 474.5 and 465.7 kJ mol−1, respectively for unirradiated samples and 429.1, 447 and 438 kJ mol−1 when the γ-irradiation reaches 30 kGy respectively. Results revealed that the values of E c decreased when the γ-dose increases and attains the minimum value at the dose of 15 kGy and then increase at higher doses. The crystallization rate factor (K) was also seen to decrease with increasing of γ-dose. Gamma irradiation increases the crystallization peak temperature (T c). The crystallization activation energy (E c) estimated from the three models is in good agreement and much well with those reported for silicate systems. Gamma irradiation decreases the E c and crystallization rate factor (K). These preliminary results can provide useful technical information for a better understanding and control of the crystallization process of this type of nanomaterial.

Preparation and characterization of MgO-Al2O3-SiO2 glass-ceramics with different MgO/Al2O3 ratio and La2O3 addition

MgO-Al2O3-SiO2 (MAS) glass-ceramics were prepared by traditional melting and sintering method, and the effects of MgO/Al2O3 ratios and La2O3 contents on the microstructure and physicochemical properties of MAS glass-ceramics were studied. Herein, differential scanning calorimetry (DSC), X-ray diffraction (XRD), fourier-transform infrared spectrophotometer (FTIR), Field-emission scanning electron microscopy (FESEM), density, corrosion resistance, dielectric properties and thermal expansion coefficient (CTE) were carried out to evaluate the properties of both parent glass and glass-ceramics samples. The results show that adjusting the MgO/Al2O3 ratio from 0.69 to 0.47 can increase the characteristic temperatures of transition temperature (Tg) and crystallization peak temperature (Tp) in MAS parent glass. The reduction of MgO/Al2O3 ratio could promotes the precipitation of α-cordierite phase (Mg2Al4Si5O18), and the grain size of α-cordierite phase were increased from 200 to 500 nm. When the MgO/Al2O3 ratio was 0.63, the MA-2 sample has the highest flexural strength of 127.46 MPa. Furthermore, we also investigated the influence of La2O3 addition on the structure and properties of MAS glass-ceramics by employed MA-2 sample as a reference. The results show both the Tg (742–748 °C) and Tp (936–943 °C) of parent glass exhibit a slightly increasing with the La2O3 content was increased from 0.0 to 2.0 wt%. The La2O3 addition show a negligible influence on the crystal phase and morphology of MAS glass-ceramics. With increasing of the La2O3 content, the MAS glass-ceramics samples have a larger density (2.58–2.76 g/cm3) and a better chemical stability, and the CTE (6.12–8.17 × 10−6/°C), εr (5.04–6.17), and the flexural strength (127.46–150.15 MPa) also show an increased change trends. The prepared MAS glass-ceramics can be packaged with high expansion coefficient chips (such as GaAs) and is expected to become a potential candidate of dielectric materials for electronic devices, especially for high frequency applications in integrated circuits.

Phase behaviors and nucleation effects of phytosterols and phytosterol esters in medium chain triglycerides

AbstractFree phytosterols (PS) and phytosterol esters (PSE) usually coexist in natural edible oils, which affect the crystallization behaviors of oil significantly. However, the phase behaviors of PS and PSE in oils and their roles on the crystallization behaviors of oil are still unclear. In this study, the isolation and dissolution behaviors of PS and PSE in medium chain triglyceride (MCT) were studied, and then their influences on the crystallization behaviors of MCT were clarified further. The results showed that when the mass ratio of PS:PSE was greater than 3:7 at the total amount of PS and PSE fixing 5 wt%, PS and PSE isolated to form a new crystal structure, which was different from PS spherical or PSE plate‐like crystal structure, in MCT. The new PS/PSE crystal structure had a larger surface area, and its melting point was between PS and PSE. It also showed the synergistic ability to promote the crystallization nucleation of MCT. When the total content of PS and PSE was 1 wt%, and the mass ratio of PS:PSE was 5:5, the crystallization peak temperature of PS/PSE/MCT was 12°C higher than that of virgin MCT, 2.5°C higher than that of PSE/MCT, and 10.3°C higher than that of PS/MCT.

Preparation of rigidity toughness balance and stable poly(glycolic acid) based on chain extension reaction

AbstractAs a completely degradable material, poly(glycolic acid) (PGA) has excellent rigidity, barrier properties, degradability and biocompatibility. However, the inherent brittleness and easily hydrolysable characteristics limit its widespread application. Herein, we introduced chain extension ADR to modify PGA to ameliorate these defects. The results showed that ADR could react with PGA to form “comb‐like” and “cross‐linked” chain extension structures resulting in the improvement of complex viscosity and formation of gel. Because of the chain entanglement of chain extension structures, the toughness of modified PGA was improved (which was verified by the impact strength value of 4.3 kJ/m2 that was about 126% of virgin PGA) without sacrificing its rigidity. Furthermore, the hydrolysis results indicated that the representative PGA/1.0ADR had better hydrolysis stability, it had more complete morphology and slower degradation rate than virgin PGA in the 17‐day hydrolysis experiment. Apart from better toughness and hydrolysis stability, there was also improvements in crystallization performance, the sample PGA/1.0ADR endowed with higher crystallization peak temperature (2.3°C higher than virgin PGA) and lower crystallization activation energy. In short, this work prepared a kind of modified PGA with rigidity toughness balance and better hydrolysis stability, which could expand the application range of PGA‐based materials.

Effects of Structural Relaxation of Glass-Forming Melts on the Overall Crystallization Kinetics in Cooling and Heating.

In the theoretical treatment of crystallization, it is commonly assumed that the relaxation processes of a liquid proceed quickly as compared to crystal nucleation and growth processes. Actually, it is supposed that a liquid is always located in the metastable state corresponding to the current values of pressure and temperature. However, near and below the glass transition temperature, Tg, this condition is commonly not fulfilled. In such cases, in the treatment of crystallization, deviations in the state of the liquid from the respective metastable equilibrium state have to be accounted for when determining the kinetic coefficients governing the crystallization kinetics, the thermodynamic driving force of crystallization, and the surface tension of the aggregates of the newly evolving crystal phase including the surface tension of critical clusters considerably affecting the crystal nucleation rate. These factors may greatly influence the course of the overall crystallization process. A theoretical analysis of the resulting effects is given in the present paper by numerical solutions of the J(ohnson)-M(ehl)-A(vrami)-K(olmogorov) equation employed as the tool to model the overall crystallization kinetics and by analytical estimates of the crystallization peak temperatures in terms of the dependence on cooling and heating rates. The results are shown to be in good agreement with the experimental data. Possible extensions of the theory are anticipated and will be explored in future analysis.

Effect of Al2O3 and BN compounding on thermal and mechanical properties of PP composites

Using polypropylene (PP) as a matrix, boron nitride (BN), and alumina (Al2O3) as fillers, PP thermally conductive composites were prepared by melt blending, injection molding and hot press molding, and the effects of BN and Al2O3 compounding on the thermally conductive, crystalline and mechanical properties of the composites were investigated. It is found that with the shear force during processing and the volume flow force of PP matrix, BN and Al2O3 can be uniformly dispersed and oriented in PP matrix, and the two synergize with each other to form a three-dimensional thermal conductivity pathway, and The thermal conductivity of the composite reaches 0.54 W m−1 K−1 when the volume shares of BN and Al2O3 is 9.09 % and 8.10 %, which is an increase of 157.14 % compared with pure PP, and the crystallization peak temperature is the highest at this time. Meanwhile, through the LED lamp heat dissipation experiment, it was found that PP/BN-9.09/Al2O3-8.25 could effectively reduce the working temperature of LED, which has excellent practical value. In addition, the compounding of BN with a small amount of Al2O3 can greatly improve the mechanical properties of the composites.

Material properties of spray‐dried cellulose nanocrystal reinforced homopolymer polypropylene composites

AbstractSpray‐dried cellulose nanocrystal (SDCNC) particles have attracted intense interest as reinforcements in polymer composites because of their unique physical and mechanical properties. This work aims to develop homopolymer polypropylene (HPP) composites with different loading levels of SDCNC particles (5, 10, 15, and 30 wt%) to understand their impact on composite mechanical, morphological, and thermal properties. The SDCNC‐reinforced HPP composites were manufactured using a C.W. Brabender bowl internal mixer with a masterbatch concept and an injection molding process. The mechanical, morphological, and thermal properties of the composites were investigated. Compared to pure HPP, the tensile, and flexural modulus of elasticity (MOE) of composites with 30 wt% SDCNC significantly increased by up to 67% and 49%. The impact strength of the composites with the absence of a compatibilizer significantly increased by up to 19%, which was attributed to the mechanical interlocking network established between SDCNC particles and HPP. Additionally, increasing SDCNC loading in the composites led to higher crystallization peak temperatures and increased the degree of crystallinity (especially at 30 wt% SDCNC content), indicating that the SDCNC particles can act as heterogeneous nucleating agents during the crystallization process. The thermal stability of the composite was slightly improved upon SDCNC introduction.Highlights With the incorporation of spray‐dried cellulose nanocrystal (SDCNC), the tensile modulus of elasticity (MOE), flexural MOE, and impact strength of filled homopolymer polypropylene (HPP) composites were significantly improved by up to 67%, 49%, and 19%, respectively. Mechanical interlocking network established between SDCNC and HPP contributed to the enhanced the impact strength. SDCNC particles can act as heterogeneous nucleating agents to promote the crystallization process of HPP. SDCNC particles slightly enhanced the thermal stability of HPP composite.

THE STRUCTURAL AND ELECTRICAL PROPERTIES OF NON-STOICHIOMETRIC CADMIUM SELENIDE THIN FILMS

Non-stoichiometric CdxSe100-x (x=10, 20, 30 at. %) alloys were prepared by melt-quenching technique, while thin films of these alloys were prepared by vacuum thermal evaporation technique. The Differential thermal analysis (DTA) results showed that the composition affects the characteristic temperatures, for instance, the glass transition, and peak crystallization temperatures. X-ray diffraction patterns (XRD) of the as-deposited films confirmed its amorphous nature except for films with x=30 at. %. These results were confirmed by scanning electron microscopy (SEM) investigations and correlated to the rigidity percolation threshold of the lattice. Furthermore, XRD patterns indicated that amorphous structures transformed into crystalline structures for annealed thin films at 423 K for 30 minutes. The microstructure parameters (crystal size, microstrain, and dislocation density) of both Se and CdSe phases were calculated for annealed films. The temperature dependence of dark d.c. conductivity of thin films was studied in the temperature range (300-500 K). The electrical measurements results showed two types of conduction mechanisms. Conduction is due to extended state in the temperature range (370-500 K) and variable range hopping in the temperature range (300-370 K). Moreover, in the high temperature range, the results indicate the validity of Meyer-Neldel rule (MNR) in the studied samples.