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1. ' Fringed micelle' model of the crystalline-amorphous structure of PC polymers. [24]  

1. ' Fringed micelle' model of the crystalline-amorphous structure of PC polymers. [24]  

Citations

... Consequently, the heat generated through the molecular vibration and friction causes the swelling and increases the viscosity of starch granules, giving a highly viscous 3D polymeric gel. During this process, the water molecules in the mixture act as a plasticizer for starch, 50 converting native starch into thermoplastic starch (TPS). The freeze-drying (lyophilization) method provides dry foam materials from the high viscosity gel. ...
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Starch and its derivatives have recently emerged as a sustainable and renewable alternative for petroleum-based expanded polystyrene (EPS) and expanded polypropylene (EPP) foam materials. In this study, biodegradable foam materials were prepared from cassava starch using a novel dual modification technique, combining microwave treatment and freeze-drying. The foam materials were prepared from starch solutions microwaved over different intervals. The starch-based foam materials were characterized using Fourier transform infrared (FTIR) spectroscopy, thermogravimetric analysis (TGA), X-ray diffraction (XRD), scanning electron microscopy (SEM), 13C nuclear magnetic resonance (13C-NMR) spectroscopy, and compression set test. Moreover, the water absorption capacities and density values of the foam materials were measured according to ASTM standards. The biodegradability test was carried out according to the aerobic compost environment test. The lowest water absorption capacities of 65.56% and 70.83% were exhibited for the cassava starch foam sample (MWB) prepared at a 20 s microwave treatment time and immersed in distilled water for 2 and 24 h, respectively. Furthermore, the lightweight cassava starch-based foam materials displayed density ranging from 124 to 245 kg/m3. The biodegradation test exhibited significant biodegradation of over 50% after 15 days for all the foam materials prepared. These results suggest that the dual-modified cassava starch-based biodegradable foams show potential in sustainable packaging applications by replacing petroleum-based materials.
... At absorption stage, the presence of hydrophilic functional groups lead to a water permeation into the scaffolds. The water act as a plasticizer which can increase the free volume between polymer chains and increase the chains mobility [52,53]. The penetration of water starts the hydrolysis process through interactions of the water molecules with hydrolyzable bonds in crosslinks, side chains and backbone of the polymers, leading to producing some degradation products and a more mobility in the polymer chains [54,55]. ...
Article
Articular cartilage is an avascular connective tissue with a slow healing rate. Tissue engineering scaffolds can provide appropriate condition to stimulate the natural healing mechanism of the damaged tissue. In this study, the electrospun nanocomposite scaffolds based on polycaprolactone (PCL)-chitosan/carboxyl-functionalized multi-walled carbon nanotubes (MWCNTs) were fabricated with different concentrations of MWCNTs including 0.5 and 1 wt%. The samples were characterized in terms of morphology, porosity, physicochemical structure, hydrophilicity, tensile strength, bioactivity, biodegradation and cell response. The scaffold containing 0.5 wt% MWCNTs presented the lowest fiber diameter (99 ± 15 nm) and the highest tensile strength (33.81 ± 6.76 MPa) (p ≤ 0.05), which were considerable for electrospun structures. The porosity percentage of the scaffolds were maintained above 80% which is appropriate for tissue engineering. As the MWCNTs increased, the water contact angle decreased due to the increase in the hydrophilic carboxyl functional groups related to the MWCNTs. MWCNTs increased the crystallinity of the scaffold, leading to a more bioactivity and stability proportional to healing rate of a natural cartilage. Chondrocytes were well cultured on the scaffold containing MWCNTs and presented more cell viability compared to the sample without MWCNTs. The PCL-chitosan/0.5wt.%MWCNTs scaffold can be considered for supplemental studies in cartilage tissue engineering applications.
... 34 This behavior can be further explained by the 'stiffening effect' by the fringed micelle theory in which, due to the heat, the 'fringe' in the amorphous regions is found to be increased. 65 One of the sources of variation in mechanical properties for WBFs is the diameter, as the methodology is being used to measure the tensile properties -that is, the single fiber method according to ASTM D3822. ...
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Biomass fibers are being widely investigated for industrial applications as an alternative to synthetic fibers using a standard humidity condition. In this study, the mechanical properties of two waste biomass fibers – canola and cattail – have been investigated when subjected to different environmental conditions, fiber length, and type of estimators used during analysis. The effect of different environmental conditions and structural variations were investigated by measuring the tensile properties after exposing them to eight different relative humidity conditions using a fixed fiber length of 25 mm. Further investigation was conducted using fiber lengths of 25, 35 and 45 mm using the most conservative relative humidity condition. The data were analyzed by a Weibull distribution model using four different estimators. The results revealed that Weibull strength ( σ avg ) and modulus (E avg ) closely followed experimental values for cattail and canola fibers. The different relative humidity conditions and fiber lengths resulted in different Weibull parameters with 11% relative humidity and the mean rank estimator predicted the most conservative tensile strength for both waste biomass fibers. The experimental and characteristic Weibull strength decreased when fiber gauge length increased from 25 to 45 mm. The tensile strength and modulus of both waste biomass fibers at 50% reliability lie within the range of average experimental values. However, these values are reduced to 155 MPa (strength) and 20 GPa (modulus) for cattail fiber at 90% reliability. The survival probability of the tensile strength and modulus were found to be the highest at 75% and 100% relative humidity for cattail and canola fibers, respectively.
... PET is thus capable of absorbing water molecules into the amorphous regions, exerting a plasticizing effect on the polymer. This absorption of water also results in a decrease in both T g and the cold crystallization temperature (T cc ) [9,10] (T cc being the temperature peak of the region where crystallization takes place). At temperatures below the T g , the amorphous chains within the PET molecules are rigid, and behave as a solid glass. ...
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This work examines the significance of the degree of polyethylene terephthalate (PET) crystallinity (XC) and glass transition temperature (Tg) on enzymatic degradation of PET at elevated temperatures using two engineered, thermostable PET degrading enzymes: LCCICCG, a variant of the leaf-branch compost cutinase, and DuraPETase, evolved from the Ideonella sakaiensis PETase. XC was systematically varied by thermal annealing of PET disks (Ø 6mm, thickness 1mm). XC affected the enzymatic product release rate that essentially ceased at XC 22-27% for the LCCICCG and at XC ∼17% for the DuraPETase. Scanning Electron Microscopy revealed that enzymatic treatment produced cavities on the PET surface when XC was >10% but resulted in a smooth surface on amorphous PET (XC ∼10%). The Tg of amorphous PET disks decreased from 74°C to 61°C during 24h pre-soaking in water at 65°C, while XC remained unchanged. Enzymatic reaction on pre-soaked disks at 65°C, i.e. above the Tg, did not affect the enzymatic product release rate, but delayed the initiation of enzymatic attack despite the lower Tg compared to enzymatic reaction on un-soaked samples. The data suggest that extended soaking of PET at 65°C induces an increase in the rigid amorphous fraction (XRAF) that impedes the enzymatic attack. These findings improve the understanding of enzymatic PET degradation and have implications for development of efficient enzymatic PET upcycling processes.
... Water is well established as a plasticizer in polymeric systems [91] and it lowers the T g of many polymers. Passerini et al. reported that undried PLGA particles contain approximate 4.47% of moisture content and have a T g of 27.7 • C, which is about 15 • C lower than that of bulk PLGA polymer Notably, the dried particles which undergo 3 days' lyophilization still contain 3.5% of residual moisture, and the T g is 33.1 • C [92]. ...
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Over recent decades, poly(lactic-co-glycolic acid) (PLGA) based nano- and micro- drug delivery vehicles have been rapidly developed since PLGA was approved by the Food and Drug Administration (FDA). Common factors that influence PLGA particle properties have been extensively studied by researchers, such as particle size, polydispersity index (PDI), surface morphology, zeta potential, and drug loading efficiency. These properties have all been found to be key factors for determining the drug release kinetics of the drug delivery particles. For drug delivery applications the drug release behavior is a critical property, and PLGA drug delivery systems are still plagued with the issue of burst release when a large portion of the drug is suddenly released from the particle rather than the controlled release the particles are designed for. Other properties of the particles can play a role in the drug release behavior, such as the glass transition temperature (Tg). The Tg, however, is an underreported property of current PLGA based drug delivery systems. This review summarizes the basic knowledge of the glass transition temperature in PLGA particles, the factors that influence the Tg, the effect of Tg on drug release behavior, and presents the recent awareness of the influence of Tg on drug delivery applications.
... [47] The most striking effect of solvent exchange is the sequestration of plasticizing water, moisture confined to the pore walls, which increases the mechanical resistance of porous polysaccharide materials. [48] Water as a solvent has a great appeal in terms of cost, stability, and toxicity, however, imposes high energy expenditure for extraction and treatment. [49] The use of scCO2 (above 31.0 ºC and 7.38 MPa) as an extractor medium for aqueous solutions, for example, presents efficiency and recovery challenges [50] arising from the solubilization of CO2 in water in the form of H2CO3(aq) and HCO3 -(aq). ...
Thesis
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Cryogels (CG), porous solids made from careful freeze-drying of aqueous gels, were based on four distinct polysaccharides (PSC) to correlate the polymer properties (such as charge, am-phiphilicity, and molar mass) and the porous material structure (in terms of pore diameter and walls thickness). Due to their chemical nature, four PSCs were chosen: carboxymethyl cellulose (CMC, negatively charged on short side chain), chitosan (CHI, positively charged), hydroxypropyl methyl-cellulose (HPMC, amphiphilic), and xanthan gum (XG, negatively charged on long side chain). The citric acid (CITR), a crosslinker, was added to the precursor gel at 2.6 x10-4 mol.L-1 concentration, and the respective CGs were subject to 165 °C for 7’. The CGs pores were characterized in terms of their homogeneity by compression strength tests (Ɛ), solvent sorption kinetics (for aqueous solutions and n-hexane), and of dyes sorption ther-modynamic (for methylene blue and rhodamine B). The porous structure itself was investigated using scanning electron microscopy (MEV) and high-resolution computer X-ray tomography (TRX) attached to 3D model quantification software. To achieve this main objective were studied the effects of changes on the precursor gel aqueous phase (pH and counter-ion) over the morphol-ogy, also the effect of changes in the size of the samples (cylindrical forms from 2 to 10 mm in diameter and 1 to 4 mm in height), and the changes in data acquisition (direction in MEV photos and image transformation constants for TRX). To modify CGs of XG and HPMC by dry route were added amino acids (AA) were to the precursor gels at 2.6 x10-4 mol.L-1 concentration (in the presence and the absence of CITR) and the respective CGs were heated at 165 °C. Due to the nature of the side chain, were used: cysteine (CIST, polar neutral), glutamic acid (GLUT, negatively charged), histidine (HIST, positively charged), and tryptophan (TRIP, apolar). In the absence of CITR, chemical linkages were not ob-served on CGAA, notably, the increase in compression modulus (Ɛ) was ought to stronger apolar interactions within the pore walls (ƐTRIP ≈ ƐCIST ≈ 2 ƐHIST ≈ 2 ƐGLUT). In the presence of CITR the crosslinking degree relayed on the molar proportion CITR:AA, notably for CGTRIP the maximal AA fixation was around 33% with CG gel content of 70% for the proportion CITR:AA of 1:1. The comprehension of the relationship between synthesis parameters and structure allowed the development of CGs with complex compositions for specific applications. “Janus cryogels” and multilayered CGs were made of 1 mm layers of native CG and alkylsililated CG attached alter-nately. Due to the hydrophobic portion, Janus CG could float in aqueous solutions or at oil/water interfaces and absorbed selectively dyes dissolved in distinct phases of oil-water mixtures. TiO2/PSC CG composites led to efficient photocatalytic adsorbents towards methylene blue degra-dation and Cr(VI) reduction.
... In submerged state there is total loss of elasticity due to water attack causing high chain scission and it results into low-molecular-weight chains. This can be ascertained by comparing sheer drop of and with loss in cross-link density (see Figs. 13e, f, and 14e) [59]. Whereas, in thermo-oxidation aging (0%RH) loss of strain is attributed to increased cross-linking (see Figs. 13b, d, f, and 14a, c, e). ...
Article
In this work, the effects of accelerated thermo-oxidative, hydrolytic and hygrothermal aging on the mechanical and chemical properties of a polyurethane based (PUB) adhesive are presented. The adhesive is extensively used in automobile industry particularly as a glass sealant. PUB is inevitably exposed to the hygrothermal environment during service life and the integrity of matrix interface is most vulnerable. This study focuses on weighing and comparing effects of different aging environments on material behavior; it showed that hygrothermal aging is a competition between two sub-aging phenomena i.e., thermo-oxidation and hydrolytic aging. Samples were exposed to 0%RH, 80%RH and submerged condition in distilled water. Uni-axial tensile tests, Differential Scanning Calorimetry (DSC) analysis, Dynamic Mechanical Analysis (DMA), Fourier Transform Infrared Spectroscopy (FTIR) Analysis, Scanning Electron Microscopy (SEM), cross-link analysis and swelling tests were carried out on as-received and aged samples. Accelerated aging process was conducted at different temperatures (60°C, 80°C and 95°C) and for different exposure durations of 1, 10, 30, and 90 days. This work confirms that the effect of hygrothermal aging is a result of competition between thermo-oxidation and hydrolytic aging environments. The total mechanical and environmental damage incurred by specimens is a collaborative effect of all exposure environments involved i.e., aging time, temperature, oxygen, water and humidity. The results are confirmed by chemical test outcomes as well.
... [47] O efeito mais marcante da troca de solvente é o sequestro de água plastificante, umidade confinada nas paredes de poro, que aumenta a resistência mecânica dos matérias porosos de polissacarídeo. [48] Água como solvente possui um grande apelo em termos de custo, estabilidade e toxicidade, entretanto, impõe alto gasto de energia para a extração e tratamento. [49] O uso de scCO2 (acima de 31.0 ºC e 7.38 MPa) como meio extrator de soluções aquosas, por exemplo, apresenta desafios de eficiência e recuperação [50] decorrentes da solubilização de CO2 em água na forma de H2CO3(aq) e HCO3 -(aq). ...
Thesis
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Foram produzidos criogéis (CG), sólidos porosos provenientes da liofilização de géis aquo-sos, a partir de quatro polissacarídeos (PSC) a fim de correlacionar propriedades do polímero (carga, polaridade e massa molar) com a estrutura das respectivas matrizes porosas (diâmetro de poro e espessura de paredes). Os PSCs escolhidos para este estudo foram carboximetil celulose (CMC, carga negativa sobre cadeia lateral curta), goma xantana (GX, carga negativa sobre cadeia lateral longa), hidroxipropil metilcelulose (HPMC, anfifílico), e quitosana (QUI, carga positiva). Para pro-mover ligações cruzadas entre as cadeias poliméricas, foram adicionados aos géis precursores 2.6 x10-4 mol.L-1 de ácido cítrico (CITR) e os CGs foram submetidos à 165 °C por 7’. Os CGs foram caracterizados quanto à sua homogeneidade por meio de ensaios de compres-são mecânica (ε), estudos de cinética de sorção de solvente (soluções aquosas e n-hexano) e termo-dinâmica de adsorção de corantes (azul de metileno e rodamina B). A estrutura porosa foi investi-gada com o auxílio de microscopia eletrônica de varredura (MEV) e tomografia computadorizada de raios-X de alta definição (TRX) atrelada à quantificação de modelos 3D. Para atingir o objetivo principal foram estudados os efeitos de variabilidade decorrente do meio precursor (pH e contra-íon) sobre a morfologia, assim como a variabilidade decorrente da dimensão das amostras (uso de molde cilíndricos variando o diâmetro de 2 à 10 mm e a espessura de 1 à 4 mm) e a variabilidade da tomada de dados (o ponto de vista do MEV e os parâmetros de transformação do TRX). A fim de promover modificação química nos CGs de GX e HPMC por via seca, foram adici-onados aminoácidos (AA) aos géis precursores na concentração de 2.6 x10-4 mol.L-1 (na presença e ausência de CITR) e os respectivos CG foram submetidos à 165 °C. Devido à natureza química da cadeia lateral foram utilizados: ácido glutâmico (GLUT, aminoácido negativo), cisteína (CIST, ami-noácido neutro), histidina (HIST, aminoácido positivo), e triptofano (TRIP, aminoácido apolar). Na ausência de CITR, não houve reticulação química dos CGAA, notadamente, interações apolares fa-voreceram a resistência à compressão εTRIP ≈ εCIST ≈ 2 εHIST ≈ 2 εGLUT. Na presença de CITR, houve graus de reticulação distintos dependendo da proporção molar CITR:AA, notadamente para CGTRIP houve fixação máxima em torno de 33% e teor de gel de 70 % para a proporção 1:1. Com os conhecimentos acumulados foi possível desenvolver CGs com composição complexa sintetizados para aplicações específicas. Sistemas multicamadas alternando CG nativo e CG alqui-lsililados com 1 mm de espessura cada, flotavam em soluções aquosas e em interfaces óleo/água, absorvendo seletivamente corantes dissolvidos em fases distintas de misturas água-óleo. CGs com-pósitos com nanopartículas de TiO2 se mostraram eficientes adsorventes fotoativos sobre irradiação a 265 nm, propiciando a degradação de azul de metileno e a redução de Cr(VI).
... Cracks may also develop because of stresses induced in the sample due to hot-cold cycles in weathering and preferential degradation of amorphous polyethylene interspersed between crystalline domains. But, the relaxation of frozen-in stress at the surface of LDPE may be facilitated in seawater due to plasticization of the polymer (Levine and Slade, 1988) by the water absorbed, especially as the absorption increases with oxidation (Jelinski et al., 1984) especially at the surface layer. Table 2 summarizes the tensile property data for the two sets of LDPE samples. ...
Article
Accelerated weathering of LDPE laminates, with samples exposed to ultraviolet radiation (UVR) in air and while floating in seawater at the same temperature, was investigated in this study. The depth profiles of the concentrations of oxidation products in the two sets of samples was assessed by FTIR (Fourier Transform Infrared Spectroscopy) and suggest the oxidation on weathering to be diffusion-controlled in both air and in seawater, localizing the reaction to a thin surface layer. While the thickness of this layer is several hundred microns in air-weathered samples it is too small to be discernible by FTIR spectroscopy in sea water-weathered samples. Studies on a naturally weathered polyethylene microplastic pellet from floating ocean debris were also similarly studied by FTIR and depth profile compared with those from accelerated weathering of LDPE laminates. Tensile properties of the LDPE weathered in air and in sea water were also compared to better understand the impact of diffusion-controlled oxidation on their mechanical integrity. How the origin of apparent retardation of the rate of weathering degradation of LDPE in seawater relative to that in air, is related diffusion-controlled oxidation due to the low concentrations of dissolved oxygen in seawater, is discussed.
... Concurrently, the use of other natural plasticizers in the development of synthetic and biopolymer-based films is discussed elsewhere [22]. From polymer science perspective, water is considered as a universal plasticizer in a food system, causing softening in the food material [23]. At the same time water is very effectively used as a plasticizer of natural and synthetic semicrystalline polymer, causing a reduction in their T g [24] and an enhancement in their free volume [25]. ...
Article
Rice starch has been used in various agri-food products due to its hypoallergenic properties. However, rice starch has poor solubility, lower resistant starch content with reduced retrogradation and poor functional properties. Hence, its industrial applications are rather limited. The lack of comprehensive information and a holistic understanding of the interaction between rice starch and endo/exogenous constituents to improve physico-chemical properties is a prerequisite in designing industrial products with enhanced functional attributes. In this comprehensive review, we highlight the potentials of physically mixing of biopolymers in upgrading the functional characteristics of rice starch as a raw material for industrial applications. Specifically, this review tackles rice starch modifications by adding natural/synthetic polymers and plasticizers, leading to functional blends or composites in developing sustainable packaging materials, pharma- and nutraceutical products other industrial applications. Moreover, a brief discussion on rice starch chemical and genetic modifications to alter starch quality for the deployment of rice starch industrial application is also highlighted.