Radiation-induced graft copolymerization of mixtures of styrene and acrylamide onto cellulose acetate. V. Studies on thermal behavior

The thermal behaviors of cellulose acetate, either grafted or ungrafted, were studied. A thermogram of cellulose acetate when grafted with acrylamide is characterized by an endothermic peak at 340°C. If, however, styrene is grafted, the thermogram shows two characteristic exothermic peaks at 330 and 420°C. A thermogram of the mixed graft comprising both acrylamide and styrene, on the other hand, is characterized by only one exothermic peak at 420°C. A consideration of various thermal data indicates that cellulose acetate when grafted is comparatively more stable than when not grafted. Again, styrene is found to be more effective than acrylamide in increasing the stability.     

H3PW12O40·4H2O as an efficient catalyst for the conversion of cellulose into partially substituted cellulose acetate

The preparation of partial acetylation of cellulose derived from rice straw was catalyzed by phosphotungstic acid with various numbers of crystal water, and H₃PW₁₂O₄₀·4H₂O was found to be as effective catalyst. The yield of the cellulose acetate was significantly enhanced by converting cellulose directly isolated from rice straw into microcrystalline cellulose before acetylation. The optimization of the acetylation was investigated by varying the amount of catalyst and acetic anhydride as well as reaction conditions including reaction time and medium, and a degree of substitution (DS) value of 2.29 and yield of 62.9% were obtained under the optimized conditions. The structure and the formation of the acetylated product were confirmed by Fourier transform infrared spectroscopy (FTIR) and powder X‐ray diffraction (XRD) technique, the thermal properties were determined by thermal analysis including thermogravimetry analysis (TGA) and differential scanning calorimetry (DSC), and the morphology was observed by scanning electron microscope (SEM). © 2014 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2015 , 132, 41212.     

Characterization and thermal stability of cellulose‐graft‐polyacryloniytrile prepared by using KMnO4/citric acid redox system

An effective condition of graft polymerization of acrylonitrile onto cellulose fiber in large volume of KMnO₄/citric acid aqueous solution was examined and the produced grafted copolymers were characterized by using SEM, NMR, FTIR, XRD, TGA, and DSC in comparison with component homopolymers. Graft yield, GY, obtained by simple weighting method was close to the value obtained by NMR analysis. Significant change of chemical structure in cellulose fiber, other than graft reaction, was not detected by NMR and FTIR measurements, whereas a decrease in the degree of crystallinity by the reaction was detected by XRD measurement. It was pointed out that thermograms for grafted samples resembles with that of cellulose at T < 370°C and become similar with that for polyacrylonitrile at T > 370°C and the mass of residue at 550°C is proportional to the content of polyacrylonitrile (GY) only. It is concluded that thermal decomposition of both polymers occurs almost independently in grafted polymers and thermal stability of cellulose fiber is not improved. © 2010 Wiley Periodicals, Inc. J Appl Polym Sci, 2010     

Mechanical and thermal characterization of native brazilian coir fiber

Coir fiber native to the Brazilian northeast coast has been characterized by mechanical, thermal, and microscopy techniques. The tensile strength, initial modulus, and elongation at break were evaluated for untreated and alkaline‐treated fibers. The results showed an enhancement of mechanical properties after 48‐h soaking in 5 wt % NaOH. The thermal stability slightly decreased after this alkaline treatment. A thermal event was observed between 28 and 38°C. The heat capacity, C_p, as a function of temperature curves between −70 and 150°C, were obtained for the untreated and alkaline‐treated coir fibers. The morphologies of the coir‐fiber surfaces and cross sections were observed by scanning electron microscopy. The properties and the morphologies were discussed, comparing the native Brazilian coir fiber with the more extensively studied native Indian coir fiber. © 2000 John Wiley & Sons, Inc. J Appl Polym Sci 76: 1197–1206, 2000     

Development of renewable resource–based cellulose acetate bioplastic: Effect of process engineering on the performance of cellulosic plastics

This paper deals with the development of a cellulose acetate biopolymer. Plasticization of this biopolymer under varying processing conditions to make it a suitable matrix polymer for bio‐composite applications was studied. In particular, cellulose acetate was plasticized with varying concentrations of an eco‐friendly triethyl citrate (TEC) plasticizer, unlike a conventional, petroleum‐derived phthalate plasticizer. Three types of processing were used to fabricate plasticized cellulose acetate parts: compression molding, extrusion followed by compression molding, and extrusion followed by injection molding. The processing mode affected the physicomechanical and thermal properties of the cellulosic plastic. Compression molded samples exhibited the highest impact strength, tending towards the impact strength of a thermoplastic olefin (TPO), while samples that were extruded and then injection molded exhibited the highest tensile strength and modulus values. Increasing the plasticizer content in the cellulosic plastic formulation improved the impact strength and strain to failure while decreasing the tensile strength and modulus values. The coefficient of thermal expansion (CTE) of the cellulose acetate increased with increasing amounts of plasticizer. Plasticized cellulose acetate was found to be processable at 170–180°C, approximately 50°C below the melting point of neat cellulose acetate.     

Thermal decomposition of a vinyl chloride/vinyl acetate copolymer

The thermal decomposition of an 85% vinyl $\text{chloride}\text{15\%}$ vinyl acetate copolymer and its different fractions obtained by precipitation was studied by the thermogravimetric scanning (t.g.s.) technique. Analyses of the t.g.s. thermograms revealed the existence of two major steps in the decomposition reaction. The first occurs between 180 and 380°C during which hydrogen chloride and hydrogen acetate are given off. In the second, which occurs between 420 and 480°C, degradation of the carbon chain takes place. Both the order of reaction and the activation energy were found to be dependent on the molecular weight of the copolymer and on the heating rate at which the experiments were carried out. Analyses of the samples carried out by gel permeation chromatography (g.p.c.) after each decomposition revealed that, besides the two steps mentioned above, yet another step, viz. crosslinking, may be taking place at 180°C or below where the weight loss of copolymer is too small to be detected by t.g.s. The process of crosslinking, however, may take place at other temperatures as well. A higher degree of crosslinking has been associated with a higher acetate content in the copolymer. A comparison of g.p.c. results with those obtained by nuclear magnetic resonance spectra showed that, out of the three steric configurations of the copolymer, syndiotactic sequences are least resistant to thermal treatment followed in order by heterotactic and isotactic sequences.     

Preparation of Rh-containing cellulose acetate films and the chemistry of Rh in cellulose acetate

RhCl [P(C₆H₅)₃]₃ complexes have been incorporated in cellulose acetate as a dispersion medium using cosolvent (tetrahydrofuran). The interactions between Rh (I) complexes and cellulose acetate (CA) are examined by infrared spectroscopy and thermal analysis. The chemical reactivities of Rh–CA films have been investigated by reacting Rh sites with CO, H₂, O₂, and C₂H₄ in the temperature range 90–150°C and at a pressure of less than 1 atm. Three different Rh-carbonyls and a Rh-hydride species formed in CA are characterized by their infrared spectra. Treatment of 10 or 20 wt % Rh–CA films with hydrogen (600 torr) at 150°C produces small Rh metal particles of ca. 10 Å or less in diameter in CA, which show catalytic activities under mild conditions in various reactions such as hydrogenation of C₂H₄, oxidation of CO, and Fischer–Tropsch type reactions.     

Effect of nanocellulose fibers and acetylated nanocellulose fibers on properties of poly(ethylene‐co‐vinyl acetate) foams

Cellulose nanofibers are promising materials in the development of polymeric foams, because they act as heterogeneous nucleation sites for the growth of cells during foaming. In this research, we studied the incorporation of cellulose nanoparticles in poly(ethylene‐co‐vinyl acetate)‐EVA foams. The foams were produced with different fiber contents. We observed the effect of a chemical treatment by acetylation on the cellulose fibber, that is, we evaluated the use of hydrophilic and hydrophobic cellulose nanofibers in EVA foams. The main results indicate that with the addition of only 1% of cellulose nanofibers, cell density significantly reduces when compared with the pure EVA foams. On the other hand, by increasing the cellulose content, the agglomeration of nanofibers also increases, which results in heterogeneous cell sizes. The same phenomenon was observed in the foams produced with acetylated cellulose nanofibers, regardless of the fiber content used. © 2017 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2017 , 134, 44760.     

Thermal and kinetic study of manganese dithionate from absorbing or leaching solution via TG/XRD/IC analysis

ABSTRACT

Mangano-manganic oxide can be prepared through thermal decomposition of manganese sulfate from the absorption or leaching solution, so desulfurization by pyrolusite or leaching pyrolusite with sulfur dioxide should be fully exploited for the recovery of manganese salt. However, upon preparing MnSO₄ using above techniques, manganese dithionate is an inevitable by-product, which lowers the purity of the industrial raw material MnSO₄ and exerts negative influences on pyrolysis technology. Information regarding thermal decomposition of solid-state manganese dithionate is scarce. To recycle manganese dithionate efficiently, pyrolysis mechanism and kinetics were systematically investigated by thermal decomposition method. The characteristics of thermal decomposition products were determined by thermogravimetric analysis techniques (TG), X-ray diffraction (XRD), and Ion chromatography (IC). The experimental results revealed that both desulfurization and following dehydration of MnS₂O₆·H₂O were a one-step process, and the desulfurization occurred at about 150°C lower than the dehydration at 230°C. As increasing pyrolysis temperature to 900°C, the manganese sulfate was firstly formed, and to 1100°C, Mangano-manganic oxide was obtained by losing sulfur oxides. Consequently, the kinetic parameters for each decomposition steps of manganese dithionate were determined by the Coasts and Redfern (CR) integral method. The as-obtained experimental and kinetic results may provide theoretical guides for recycling manganese dithionate.     

Preparation and mechanism analysis of morphology-controlled cellulose nanocrystals via compound enzymatic hydrolysis of eucalyptus pulp

First, making from eucalyptus cellulose fiber, the influences of different compound enzymolysis conditions on the morphology of cellulose nanocrystals (CNCs) were studied. Under the actions of the compound enzyme composed of cellulase and xylanase with the concentration ratio of 9:1, total enzyme concentrations of 10 and 500 U mL⁻¹ and the hydrolysis time of 12 and 5 h, the rod-like CNCs (length 600 nm, width 30 nm) and the spherical CNCs (40 nm) were obtained, respectively. Subsequently, the crystallinities, chemical structures, and thermal stabilities of the rod-like and spherical CNCs revealed that, the CNCs structures were still similar to those of the eucalyptus cellulose fiber, the thermal decomposition temperatures of the rod-like and spherical CNCs (345, 343 °C) were a little lower than that of the eucalyptus cellulose fiber (364 °C). Lastly, the control mechanism of CNC morphology by the compound enzymatic hydrolysis was also discussed. © 2019 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2020 , 137, 48407.     

A new approach for the production of cellulose acetate: Acetylation of mechanical pulp with subsequent isolation of cellulose acetate by differential solubility

A heretofore uninvestigated approach to the production of cellulose acetate, the acetylation of whole wood pulp with subsequent isolation of the cellulose derivative by differential solubility, is described. The mechanical pulp used was produced by refining aspen wood chips with a disc refiner. Two conventional acetylation techniques, the fibrous and solution process, were employed to acetylato all components of the pulp. The cellulose acetate was isolated from the acetylated lignin and hemicellulose by dissolving in dichloromethane/methanol (9:1, v/v). The advantage of this new approach is that the high cost involved in using an extensively purified dissolving pulp are avoided. Both acetylation techniques yielded a product that was about 84% cellulose acetate. The remaining acetylated components were lignin and hemicellulose. The yield of cellulose acetate, based on the cellulose content of the original pulp and the product, was 75–80%.     

Coconut water as a potential resource for cellulose acetate membrane preparation

BACKGROUND: Cellulose acetate membranes are frequently used for pressure‐driven membrane processes. The aim of this work was to prepare cellulose acetate membranes from nata‐de‐coco using coconut water as starting material. The use of this lignin‐free material will certainly minimize the use of chemicals usually needed in the traditional pulps and substitute for the use of wood, which helps prevent global warming and preserves nature as well. RESULTS: Coconut water was fermented by Acetobacter xylinum for 6 days to produce nata‐de‐coco, which was then acetylated to produce cellulose diacetate with an acetyl content of 39.6%. Fourier transform infrared analysis showed characteristic peaks for the acetyl group at 1748 and 1236 cm^?1. The resulting membranes made from the hydrolysis product showed a water flux of 210.5 L m^?2 h^?1 under an applied pressure of 2 kg cm^?2 while the rejection coefficients of dextran T‐500 and T‐2000 solutions were 78 and 93.7%, respectively. CONCLUSION: Coconut water has a potential to be used in the fabrication of membranes by converting it to nata‐de‐coco and then to cellulose diacetate which gives an added value to its original nature. It is also highly competitive compared to the traditional pulps, by which acetylation decreases the degree of crystallinity of nata‐de‐coco resulting in higher membrane permeability. Copyright © 2007 Society of Chemical Industry     

Engineering Lignocellulose Fibers with Higher Thermal Stability through Natural Fiber Welding

This study reveals how natural fiber welding (NFW) can be used to engineer biopolymer materials with improved thermal stability. First, it is shown how NFW without binders improves lignocellulose yarn thermal stability by ≈17 °C, primarily by condensing microfibril structure. Next, silanized‐cellulose nanofibrils (Si‐CNFs) are developed as NFW binders; this silanization process alters CNF physical and thermal properties. During pyrolysis, Si_x O_y networks form, which delay CNF decomposition (up to 37 °C), slow cellulose mass loss rates (up to 89%), and can enhance char yield more than twofold. When used as NFW binders, Si‐CNFs increase lignocellulose yarn thermal stability (up to 17 °C) proportional to siloxane amount, and can reduce cellulose mass loss rates (≈25% compared to welding without binder). These exciting results highlight the potential of NFW as a green‐engineering process to transform natural fibers into more thermally stable, biocomposite textile yarns.     

Membrane potential measurements on cellulose acetate membranes

Membrane potentials and apparent transport numbers of the cation are reported for cured cellulose acetate membranes bounded by HCl, NaCl, KCl and MgCl₂ solutions, using Ag/AgCl electrodes and a flow-cell method. Membranes cured at 70°, 80° and 90° are used. Bounding solution concentrations vary from 0.005 to 0.05 M at the high concentration side (bounding the dense side of the membrane), and are kept constant at 0.002 M for the low concentration solution. In the KCl 90° membrane case the low concentration solution is varied as well, from 0.0001 to 0.002 M. Results show that cured cellulose acetate membranes are permselective towards univalent cations. This is interpreted as resulting from a low cation-exchange capacity of the dense layer of the cured membrane. The permselectivity increases with increased curing temperature. Addition of a non-electrolyte to the low concentration side reverses the osmotic flow and leads to higher apparent transport numbers of the cation. It is concluded that diffusion in small pores contributes significantly to the transport of ionic solutes through uncompacted membranes.     

Effect of surface treatments on the thermal behavior and tensile strength of piassava (Attalea funifera) fibers

Piassava (Attalea funifera) fibers subjected to several surface chemical treatments and as‐received raw fibers were compared with respect to their thermal and tensile behaviors. The thermal degradation of the raw fibers was characterized by three main stages that corresponded to water release at low temperatures, decomposition of hemicellulose, and decomposition of α cellulose. Mercerization acted mainly on hemicellulose removal, and there was no change in the hydrophilic behavior of the fibers. The removal of hemicellulose split the fibers into microfibrils and favored the thermal decomposition of α cellulose. The same behavior was observed when the fibers were subjected to mercerization and acetylation. The fibers subjected to only acetylation showed thermal behavior similar to that of the raw fibers. With the acetylation treatment, a minor decrease in the hydrophilic character of the fibers was noted. Despite some differences in the thermal behavior, the tensile strengths of the raw and treated fibers were statistically equal. Complementary Fourier transform infrared and scanning electron microscopy analysis corroborated the thermogravimetric analysis/differential thermogravimetry results. © 2010 Wiley Periodicals, Inc. J Appl Polym Sci, 2011     

Morphology and mechanical properties of nanocomposites of cellulose acetate and organic montmorillonite prepared with different plasticizers

Nanocomposites of cellulose acetate and an organically modified montmorillonite (CA/MMTO) were prepared by melt intercalation in a twin‐screw extruder, using two different plasticizers: di‐octyl phthalate (DOP) and triethyl citrate (TEC). The influence of plasticizer type and the organoclay added to the structure, the morphology, and the thermal properties of the nanocomposites was investigated. XRD and SAXS results indicated a significant CA or/and plasticizer intercalation in the clay gallery for the CA/MMTO nanocomposites. In addition, the images obtained by TEM show that the morphology of CA/MMTO nanocomposites is made up of intercalated and exfoliated silicate layers. The glass transition temperature (T_g) of CA with DOP or TEC decreased in at almost same value, which shows the characteristics of both additives as plasticizers for cellulose acetate chains. Tensile tests indicate that the nanocomposites with either of the two plasticizers presented the same performance with respect to material properties. The results demonstrated that, for some applications, TEC is an useful alternative to plasticize CA in order to substitute DOP, a non eco‐friendly plasticizer. © 2011 Wiley Periodicals, Inc. J Appl Polym Sci, 2011     

Thermal characteristics of ethylene‐co‐vinyl acetate/cellulose microfibers composites

Cellulose microfibers were obtained from Hibiscus sabadariffa by steam explosion technique. Structural and surface analysis of the microfibers showed a reduction in diameter and changes in surface morphology from that of raw fibers. The chemical composition of fibers showed increase in α‐cellulose content and decrease in lignin and hemicelluloses for the microfibers. These factors were further confirmed by XRD, SEM, and FTIR results. The CMF were introduced to EVA at different loading by melt extrusion. The composites were analyzed for their thermal stability and phase transition using thermogravimetric analysis (TGA) and differential scanning calorimetry (DSC). TGA analysis of the composites showed increased onset temperatures for composites compared with pure EVA indicating the superior thermal stability of the composites with fiber loading. DSC analysis shows increase in melting enthalpy and percentage crystallinity with fiber loading increases. Kinetic parameter for the degradation of the composites was obtained using Broido, Coats–Redfern, and Horowitz‐Metzger methods. POLYM. COMPOS., 2013. © 2013 Society of Plastics Engineers     

Cellulose acetate: Interactions with aqueous phenol and a transition temperature of about 20°C

Sorption of aqueous phenol onto powdered cellulose acetate can be described with the Langmuir equation at phenol concentrations below 0.10M. Unacetylated hydroxyl groups are probably the primary sites where phenol hydrogen bonds. As the phenol concentration is increased (> 0.13M), additional hydrogen bonding may occur with the carbonyl oxygens on the primary acetate groups, followed by secondary acetates and the beta glucosidic oxygens. Sorption at higher concentrations shows a negative slope for the Langmuir equation, perhaps caused by crowding and partial blocking of sites. Extrapolations to higher phenolic concentrations using the equation from the negative slope isotherm and plotting N versus °C reveal two lines with a point of intersection at 0.77M. Because of the increase slope above 0.77M, cellulose acetate may be dissolving in phenol. At concentrations below 0.10M, two processes were identified using a Van't Hoff plot (9.33 ± 0.30) × 10³ and (?1.36 ± 0.18) X 10³ J/mol. The initial moisture present in the polymer appears to be an important experimental variable and a transition temperature of 20.1 ± 0.2°C, probably due to polymer swelling, is reported.     

Recycled milk pouch and virgin low‐density polyethylene/linear low‐density polyethylene based coir fiber composites

The viability of the thermomechanical recycling of postconsumer milk pouches [a 50 : 50 low‐density polyethylene/linear low‐density polyethylene (LDPE–LLDPE) blend] and their use as polymeric matrices for coir‐fiber‐reinforced composites were investigated. The mechanical, thermal, morphological, and water absorption properties of recycled milk pouch polymer/coir fiber composites with different treated and untreated fiber contents were evaluated and compared with those of virgin LDPE–LLDPE/coir fiber composites. The water absorption of the composites measured at three different temperatures (25, 45, and 75°C) was found to follow Fickian diffusion. The mechanical properties of the composites significantly deteriorated after water absorption. The recycled polymer/coir fiber composites showed inferior mechanical performances and thermooxidative stability (oxidation induction time and oxidation temperature) in comparison with those observed for virgin polymer/fiber composites. However, a small quantity of a coupling agent (2 wt %) significantly improved all the mechanical, thermal, and moisture‐resistance properties of both types of composites. The overall mechanical performances of the composites containing recycled and virgin polymer matrices were correlated by the phase morphology, as observed with scanning electron microscopy. © 2007 Wiley Periodicals, Inc. J Appl Polym Sci, 2007     

Dissolution and characterization of regenerated Antheraea pernyi silk fibroin

Dissolution of Antheraea pernyi silk fiber was carried out in a calcium nitrate solution with various dissolving conditions. The solubility was significantly dependent on the concentration of calcium nitrate, dissolving temperature, and time. The proper conditions of dissolution were found as 7M calcium nitrate, 100°C temperature, and 3 h dissolving time. The aqueous solution of A. pernyi silk fibroin was composed of a mixture of polypeptides with several molecular weights above 14 kDa. FTIR and XRD showed that regenerated A. pernyi silk fibroin was composed of an α-helix as well as a random-coil conformation while silk fiber had a traditional β-sheet structure. The endo–exo transition in the temperature ranges of 228–232°C also supports these conformations of regenerated silk fibroin film. TGA and DTG curves showed that the thermal decomposition of regenerated A. pernyi silk fibroin proceeded by three steps, not dependent on the conformation. The mechanical damping peaks (tan δ) appeared about 227°C with a minor shoulder maximum about 240°C, which were somewhat lower than those of tussah silk fiber. © 2001 John Wiley & Sons, Inc. J Appl Polym Sci 82: 750–758, 2001