Thermal properties of microcrystalline cellulose-filled PET–PTT blend polymer composites

Polymer composite materials were prepared from poly(ethylene terephthalate)–poly(trimethylene terephthalate) blends as the matrix and different microcrystalline cellulose (MCC) filler levels (0–40 wt%) using melt compounding followed by compression molding. The composites were analyzed using dynamic mechanical thermal analysis (DMTA), differential scanning calorimetry (DSC) and thermogravimetric analysis (TG). The DSC results indicated that there is no consistent or significant influence of the MCC addition on the glass transition (T _g), melting (T _m), and crystallization temperature of the composites. With increasing MCC content, dynamic mechanical properties improved because of the reinforcing effect of the MCC. The tan δ peak values from the DMTA were not significantly changed as the MCC content increased. TG indicated that the onset temperature of rapid thermal degradation decreased with increasing MCC content. It was also found that the thermal stability of the composites slightly decreased as the MCC content increased.     

Evaluation of the performance of microcrystalline cellulose in retarding degradation of two epoxy resin systems

Accelerated weathering studies are necessary to determine future risks arising from the loss of durability of materials under environmental conditions (e.g. ultraviolet irradiation from the sun, moisture from rainfall, temperature cycling). The influence of different accelerated weathering conditions such as UV light and moisture on the properties of two epoxy resin systems incorporating microcrystalline cellulose (MCC) was evaluated. This study aimed to assess changes in chemical properties (FTIR), mechanical properties (tensile tests), thermal properties (TGA and DSC) and morphology (SEM) before and after accelerated weathering. The samples exposed to different accelerated weathering times (1, 2, 3, 4, and 6?months) were based on the diglycidyl ether of bisphenol A, DGEBA, or hydrogenated diglycidyl ether of bisphenol A, HDGEBA, with amine crosslinker (2,2,4-trimethyl-1,6-hexanediamine, TMDA) and 2% MCC. Incorporation of MCC improved thermal stability, reduced surface oxidation, and gave better retention of mechanical properties after accelerated weathering. Both epoxy resins and epoxy composites exhibited a reduction in the tensile strength upon accelerated weathering with the composites showing less reduction in the tensile strength after 6 months. The glass transition temperatures (T_g) before and after accelerated weathering were also measured. DGEBA-TMDA/2%MCC and HDGEBA-TMDA/2% MCC composites reduced the decrease in the T_g after accelerated weathering, compared to that of DGEBA-TMDA and HDGEBA-TMDA samples. Degradation primarily decreased the mechanical properties of the composites, with some damaged specimens showing on the surfaces of DGEBA-TMDA/2% epoxy composites and HGEBA-TMDA/2%MCC composites. Fewer morphological changes with limited voids were seen on the DGEBA epoxy interface for HDGEBA compared to DGEBA composite samples. Incorporation of 2%MCC in DGEBA-TMDA and HDGEBA-TMDA increased resistance to thermal degradation after accelerated weathering.     

Effect of microcrystalline and nanocrystals cellulose fillers in materials based on PLA matrix

The aim of this work was to compare the effects of microcrystalline cellulose (MCC) and cellulose nanocrystals (CNC) addition on the properties of PLA matrix. The CNC were obtained by acid hydrolysis of the MCC. Both MCC and CNC were separately incorporated in PLA at ratios of 3, 5 and 7 wt%. In some compositions, organophilic silica (R972) was added to improve the cellulose-matrix compatibility. The properties of the materials were evaluated by FTIR, XRD, NMR and mechanical tests. Functional groups and crystalline structure of MCC and CNC were determined by FTIR and XRD, respectively. NMR T₁H values showed that films containing CNC presented better interfacial interaction than those containing MCC, and indicated that R972 acts as compatibilizer. MCC and CNC acted as nucleating agents for PLA crystallization and there was an improvement in the mechanical performance of materials with the addition of CNC.     

Glass transition temperature and thermal decomposition of cellulose powder

Cellulose powder and cellulose pellets obtained by pressing the microcrystalline powder were studied using differential scanning calorimetry (DSC), differential thermal analysis (DTA), and thermal gravimetry (TG). The TG method enabled the assessment of water content in the investigated samples. The glass phase transition in cellulose was studied using the DSC method, both in heating and cooling runs, in a wide temperature range from −100 to 180 °C. It is shown that the DSC cooling runs are more suitable for the glass phase transition visualisation than the heating runs. The discrepancy between glass phase transition temperature T _g found using DSC and predictions by Kaelbe’s approach are observed for “dry” (7 and 5.3% water content) cellulose. This could be explained by strong interactions between cellulose chains appearing when the water concentration decreases. The T _g measurements vs. moisture content may be used for cellulose crystallinity index determination.     

Phase transformations in microcrystalline cellulose due to partial dissolution

All-cellulose composites were prepared by partly dissolving microcrystalline cellulose (MCC) in an 8.0 wt% LiCl/DMAc solution, then regenerating the dissolved portion. Wide-angle X-ray scattering (WAXS) and solid-state ¹³C NMR spectra were used to characterize molecular packing. The MCC was transformed to relatively slender crystallites of cellulose I in a matrix of paracrystalline and amorphous cellulose. Paracrystalline cellulose was distinguished from amorphous cellulose by a displaced and relatively narrow WAXS peak, by a 4 ppm displacement of the C-4 ¹³C NMR peak, and by values of T₂(H) closer to those for crystalline cellulose than disordered polysaccharides. Cellulose II was not formed in any of the composites studied. The ratio of cellulose to solvent was varied, with greatest consequent transformation observed for c < 15%, where c is the weight of cellulose expressed as % of the total weight of cellulose, LiCl and DMAc. The dissolution time was varied between 1 h and 48 h, with only small additional changes achieved by extension beyond 4 h.     

Efficient barrier properties of mechanically enhanced agro-extracted cellulosic biocomposites

The objective of this work was to prepare the mechanically stable hydrophobic biocomposites by incorporating the cellulose fibers into the polymer matrices for their applications in biomedical and food packaging. Herein, two different types of biocomposites were prepared by mixing polylactic acid (PLA) and polyhydroxybutyrate (PHB) with the agro-extracted cellulose, separately at 170 °C. The influence of the cellulose fibers on the thermal, mechanical, and barrier properties of polymer matrices (PLA and PHB) was observed. With an increase in the cellulose content in PLA and PHB, the tensile strength of the biocomposite materials significantly improved with the enhancement of 24.45% and 32.08%, respectively, compared with the pure PLA and PHB. Furthermore, a decrease of 74.16% and 73.49% in the water vapor transmission rate and oxygen transmission rate, respectively, was observed for cellulose/PHB biocomposites. This study highlights that adding cellulose fibers significantly improves the mechanical and the barrier properties of PLA and PHB, suggesting their biocomposites for use in biodegradable polymer industries.     

Effects of poly(ethylene glycol) on the morphology and properties of biocomposites based on polylactide and cellulose nanofibers

Polylactide (PLA)/cellulose nanofiber (CNF) biocomposites were prepared via solution casting and direct melt mixing. To improve the compatibility, a masterbatch of CNFs and poly(ethylene glycol) (PEG) (1:2) was also prepared. The effects of PEG on the morphology and properties of the biocomposites were investigated. The dispersion/distribution of nanofibers in PLA was improved when the masterbatch was used and the composites were prepared in solution. Substantial effects on the rheological properties of solution-prepared PLA/CNF/PEG composites were observed compared to composites containing no PEG, whereas for melt-prepared composites no significant changes were detected. Increased crystalline content and crystallization temperature were observed for the composites prepared via the masterbatch and solvent casting. The storage modulus of PLA was increased by 42 and 553% at 25 and at 80 °C, respectively, for the solution-based PEG-compatibilized composite containing 2 wt% nanofibers. Also, a better light transmittance was measured for the PLA/CNF/PEG composites prepared in solution.     

Thermal analysis and crystallinity study of cellulose nanofibril-filled polypropylene composites

The isothermal and non-isothermal decompositions of cellulose nanofiber (CNF) and microfibrillated cellulose (MFC)-filled polypropylene (PP) composites were evaluated and compared with microcrystalline cellulose (MCC)-filled composites by means of thermogravimetric analysis (TG). X-ray diffraction was employed to evaluate crystallinity of the composites. The degree of maximum thermal degradation (ultimate DTG peak value) increased and thermal degradation onset temperature decreased as the cellulose content increased because the thermal stability of cellulose fillers is lower than that of neat PP, but the thermal degradation of the composite was hindered at higher temperature conditions because of the increased residual mass content of the cellulose nanofibril fillers compared to the matrix polymer. The isothermal residual mass of the cellulose nanofibril-filled PP composites under melt blending and injection molding temperatures was decreased marginally by incorporation of the cellulose reinforcement but still exhibited considerable isothermal stability. The raw materials and composites examined in this study were not affected by the manufacturing process temperatures utilized to produce the composites. The MCC decreased the composite crystallinity while the nano-sized cellulose (CNF and MFC) did not appear to have an effect on crystallinity.     

Polymeric biocomposites of poly (butylene adipate-co-terephthalate) reinforced with natural Munguba fibers

In this work, polymeric biocomposites of poly (butylene adipate-co-terephthalate), PBAT, were reinforced with Munguba fibers (Pseudobombax munguba). This tree is found in great abundance in the marshy areas of the Amazon forest. The motivation for using this fiber in polymer composites comes from the fact that although research for this fiber has not been reported in the scientific literature, it is commonly used by the local population because its bark is strong and flexible. Most important is that the extraction of Munguba fibers does not damage the supplier tree because as it is extracted from the bark, its regeneration starts as it is removed. The fibers were chemically treated by mercerization/acetylation and evaluated by Fourier transform infrared spectroscopy, thermogravimetric analysis and tensile tests. The Munguba fiber presented mechanical properties similar to those of other natural fibers traditionally used in composites, and the chemical treatment provided improvements of its thermal stability and stiffness. The biocomposites showed a better elastic modulus in relation to the pure PBAT. The addition of fibers caused changes in the T _g, T _m and T _c of PBAT as observed by differential scanning calorimetry analysis. The Russel, Halpin-Tsai and Maxwell models were employed to provide the theoretical elastic modulus of the biocomposites.     

Cellulose nanofibril-reinforced biodegradable polymer composites obtained via a Pickering emulsion approach

Preparation of cellulose nanofibril (CNF)-reinforced, biodegradable polymer composites is challenging in that it’s hard to achieve good dispersion of the hydrophilic cellulose fibers in a hydrophobic polymer matrix. In this work, we developed a surfactant-free and efficient process to prepare CNF-reinforced poly (lactic acid) (PLA) composites from an aqueous dichloromethane Pickering emulsion self-emulsified by CNFs. CNF/PLA composites of homogeneous dispersion were obtained upon evaporation of CH₂Cl₂, filtration, drying and hot-pressing. Differential scanning calorimetry measurement revealed an enhanced crystallization capacity of the CNF/PLA composites. Thermogravimetric analysis indicated an increase of onset degradation temperature. The composites displayed an enhanced storage modulus compared with neat PLA throughout the testing temperature range, and especially in the high-temperature region (>70 °C). Enhancements of the flexural modulus and strength were also achieved.     

Thermal properties of poly(lactic acid)/organo-montmorillonite nanocomposites

Poly(lactic acid)/organo-montmorillonite nanocomposites were prepared by melt intercalation technique. Maleic anhydride-grafted ethylene propylene rubber (EPMgMA) was added into the PLA/OMMT in order to improve the compatibility and toughness of the nanocomposites. The samples were prepared by single screw extrusion followed by compression molding. The effect of OMMT and EPMgMA on the thermal properties of PLA was studied. The thermal properties of the PLA/OMMT nanocomposites have been investigated by using differential scanning calorimeter (DSC) and thermo-gravimetry analyzer (TG). The melting temperature (T _m), glass transition temperature (T _g), crystallization temperature (T _c), degree of crystallinity (χ_c), and thermal stability of the PLA/OMMT nanocomposites have been studied. It was found that the thermal properties of PLA were greatly influenced by the addition of OMMT and EPMgMA.     

Synthesis and characterization of microcrystalline cellulose produced from bacterial cellulose

In this study, microcrystalline cellulose (MCC) was prepared from the acid hydrolysis of bacterial cellulose (BC) produced in culture medium of static Acetobacter xylinum. The MCC-BC produced an average particle size between 70 and 90 μm and a degree of polymerization (DP) of 250. The characterization of samples was performed by thermogravimetric analysis, X-ray diffraction, and scanning electron microscopy (SEM). The MCC shows a lower thermal stability than the pristine cellulose, which was expected due to the decrease in the DP during the hydrolysis process. In addition, from X-ray diffractograms, we observed a change in the crystalline structure. The images of SEM for the BC and MCC show clear differences with modifications of BC fiber structure and production of particles with characteristics similar to commercial MCC.     

Development and thermal behaviour of ternary PLA matrix composites

Biodegradable PLA composites were prepared using microcrystalline cellulose (MCC) and silver (Ag) nanoparticles. The main objective of the present study is to develop new biopolymer composites with good mechanical properties, thermal stability, maintaining the optical transparency and also providing antimicrobial properties through silver nanoparticle introduction. Composites were prepared with 1%wt of Ag nanoparticles and 5%wt of MCC using a twin-screw microextruder; film parameters were optimized in order to obtain a thickness range between 20 and 60 μm.PLA composites maintained optical transparency properties of the matrix, while MCC was able to reduce polymer permeability. Thermal analysis revealed that MCC increased PLA crystallinity and the mechanical properties of the composites demonstrated that tensile modulus was improved by microcrystalline cellulose.     

Biodegradable Composites of Poly(lactic acid) with Cellulose Fibers Polymerized by Aluminum Triflate

Biodegradable polymer composites consisting of poly(lactic acid) (PLA) and cellulose fibers (CF) were prepared by our newly developed method. L-Lactic acid (LA) was reacted by ring-opening polymerization with aluminum triflate as a catalyst, glycerol as an initiator and CF as a filler, in simple plastic tubes at 100 °C for 6 hours. By this method, CF could be mixed with the polymer matrix easily and homogeneously. The molecular weight and molecular weight distribution of the PLA matrix were determined by gel permeation chromatography (GPC). The M_n of the composite samples decreased from 6200 to 2800 with increasing CF content. The molecular weight distribution of composites was around 2.5 regardless of the CF content. Biodegradation of samples was determined by measuring the results from the Microbial Oxidative Degradation Analyzer (MODA) and the weight loss in compost. Biodegradation of composite samples of PLA with CF increases with increasing CF content as measured by the MODA. Apparent density of composite samples was calculated by using the weight and sizes of column shape specimens. The density of the composite samples was a bit lower than that of PLA pure samples without CF. Mechanical properties such as the elastic modulus and strength were investigated by compression tests using column shape specimens. For the sample with filter paper as CF, the strength of composite samples increases with increasing CF content.     

The thermal expansion of cellulose II and IIIII crystals

Highly crystalline samples of cellulose II and III_II have been prepared from repeated mercerization of ramie fibers and supercritical ammonia treatment of the mercerized ramie fibers, respectively. The thermal expansion behavior of cellulose II and III_II was investigated using X-ray diffraction at temperatures ranging from room temperature to 250 °C. With increasing temperature, the unit cell of cellulose II expanded in the lateral directions and contracted in the longitudinal direction, with the a and b axes increasing by 0.54 and 3.4%, respectively, and the c axis decreasing by 0.09%. The anisotropic thermal expansion in these three directions was closely related to the crystal structure and the hydrogen bonding in cellulose II. A similar anisotropic thermal expansion was also observed in cellulose III_II. Cellulose III_II expanded in the lateral direction but contracted in the longitudinal direction.     

Thermo-mechanical properties of microfibrillated cellulose-reinforced partially crystallized PLA composites

Polylactic acid (PLA) in a crystallized state has mechanical properties at high temperatures superior to PLA in an amorphous state. However, a long annealing time is required to fully crystallize PLA. In this study, microfibrillated cellulose (MFC)-reinforced partially crystallized PLA composites were produced, with the goal of reducing the time required to fabricate PLA parts. A series of PLA/MFC composites at a fiber content of 10 wt% from degree of crystallinity (Xc) 0 to 43% was obtained by annealing at 80 °C. Although the annealing time required to obtain a composite (Xc: 17%) was only around one-seventh of the 20 min needed to fully crystallize neat PLA (Xc: 41%), both materials had comparable rigidity above the glass transition temperature (T _g) and creep deformation at around T _g. These results showed that partially crystallized PLA/MFC composite can replace fully crystallized neat PLA.     

Effect of compatibilization on thermal degradation kinetics of HDPE-based composites containing cellulose reinforcements

Dynamic thermogravimetric analysis under nitrogen flow was used to investigate the thermal decomposition process of high-density poly(ethylene) (HDPE)-based composites reinforced with cellulose fibers obtained from the recycling of multilayer carton scraps, as a function of the cellulose content and the compatibilization. The Friedman, Flynn–Wall–Ozawa, and Coats–Redfern methods were used to determine the apparent activation energy (E _a) of the thermal degradation of the cellulose component into the composites. E _a has been found dependent on the cellulose amount and on the cellulose/polymer matrix interfacial adhesion. In particular, it has been evidenced an increase of the cellulose thermal stability as a consequence of the improved interfacial adhesion between the components in NFR composites.     

Determination of empirical polarity parameters of the cellulose solvent N,N-dimethylacetamide/LiCl by means of the solvatochromic technique

Empirical solvatochromic polarity parameters (α-, β-, and $ \pi ^* $, AN and DN, as well as E_T(30)-values) for cellulose, N,N-dimethylacetamide (DMA)/LiCl and cellulose dissolved in DMA/LiCl are presented. The following solvent polarity indicators were applied: 2,6-diphenyl-4-(2,4,6-triphenyl-1- pyridinio)-1-phenolate ( 1 ), bis(4-N,N-dimethylamino)-benzophenone (MK, 2 ), iron(II)-di-cyano-bis(1,10)-phenanthroline, Fe(phen)₂(CN)₂, ( 3 ), and copper(II)-N,N,N′,N′-tetramethyl-ethylendiamine-acetylacetonate tetraphenylborate/chloride/bromide (Cu(tmen)(acac)⁺ X⁻ ( 4 )). The solvatochromic shifts (ν_max) of the indicators 1 , 2 , 3 , and 4 adsorbed to cellulose or dissolved in DMA/LiCl reflect the corresponding properties of the surrounding, the dipolarity/polarizability ($ \pi ^* $), the hydrogen bond donating ability or Lewis acidity (α), and the hydrogen bond accepting ability or Lewis basicity (β), respectively. Any indicator employed is well characterized (r > 0.97) by a linear solvation energy relationship (LSER) taking the Kamlet and Taft parameter into account: ν_max(indicator) = ν_max,0 + s$ \pi ^* $ + aα + bβ. Cellulose, DMA/LiCl, and the cellulose/DMA/LiCl solution approach a similar polarity with an E_T(30) parameter about 52 to 53 kcal mol⁻¹. The hypothetical interaction strength parameter (acid-base interactions, dipolar–dipolar interactions) between cellulose and DMA/LiCl are calculated by means of the individual Kamlet–Taft parameters α, β, and $ \pi ^* $ of cellulose and DMA/LiCl via a multiparameter equation. The specific chloride/cellulose interaction plays a dominant role in the cellulose solvent DMA/LiCl. Comparison of the polarity parameters of DMA/LiCl with the polarity parameters of other mixtures—such as N,N-dimethyl- formamide/LiCl, DMA/NaCl, or DMA/LiBr—are presented as well. © 1998 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 36: 1945–1955, 1998     

Photodegradation of cellulose acetate fibers

The photodegradation of cellulose acetate fibers by ultraviolet light in vacuo at 77°K and at ambient temperature was studied. Three kinds of light sources with different wavelengths between 2353 and 6000 Å were employed. ESR studies at 77°K show that several kinds of free radicals are produced from cellulose diacetate (CDA) and cellulose triacetate (CTA) fibers when irradiated with light of wavelength shorter than 2800 Å. Among these methyl radicals formed decayed within 210 min at 77°K. When the temperature was raised above 77°K, radical transformation occurred at 87°K and most of the free radicals decayed at 193°K, whereas the cellulosic radicals were stable at this and even at higher temperatures. Ultraviolet spectroscopy studies revealed that the main chromophores are the carbonyl function of the acetyl group and acetal groups in the polymer. The photodegradation of the polymers at ambient temperature resulted in the formation of gaseous products (mainly CO, CO₂, and CH₄), together with the loss of bound acetic acid content and sample weight. Decreases in viscosity and reduction of tensile strength and elongation were also observed in the irradiated samples, revealing that the overt effects of ultraviolet light on cellulose acetate fibers are interpreted in terms of free-radical reactions ultimately leading to main-chain and side-group scissions, unsaturation, and the formation of small molecule fragments. Among these, main-chain scission took place predominantly in CDA fiber and side-group scission in CTA fiber. The mechanism of the fundamental photochemical degradation processes of cellulose acetate fibers is elucidated.     

The synergetic effect of phenylphosphonic acid zinc and microfibrillated cellulose on the injection molding cycle time of PLA composites

This study evaluates the effects of nucleants phenylphosphonic acid zinc (PPA-Zn) and talc, mold temperature, and microfibrillated cellulose (MFC) reinforcement in the acceleration of injection molding cycle of polylactic acid (PLA). PLA was dissolved in an organic solvent, mixed with nucleant and MFC, and dried compounds were injection molded into molds at temperatures ranging from 40 °C to 95 °C and holding times from 10 s to 120 s. Our results showed that PPA-Zn is more effective nucleating agent compared to talc. The addition of 1 wt% PPA-Zn and the mold temperature of 95 °C exhibited the fastest crystallization rates for the molded PLA, however, at this temperature the parts could not be quickly ejected without distortion. Addition of 10 wt% MFC increased the stiffness of PLA at high temperatures and allowed ejection of parts without distortion at a holding time of just 10 s. At this holding time, the crystallinity of the PLA composite was 15.3% but the storage modulus above T _g was superior to that of fully crystallized neat PLA due to MFC reinforcement, retaining the shape of the molded part during demolding. The mechanical properties of the composite at room temperature were also higher than those of fully crystallized neat PLA.