Novel techniques to investigate the impact of cellulose esters on the rheological properties and appearance in automotive basecoat systems

The viscous response of a coating formulation changes over several orders of magnitude after application onto a substrate. Furthermore, the performance and application attributes for a refinish basecoat formulation are slightly different from those of an OEM basecoat. The absence of a high temperature baking step during the refinish process necessitates that the paint exhibit very good antisag behavior as well as quick ‘dry to touch’ without compromising the flow and leveling properties of the coating as it dries. As most paint formulations are multicomponent in nature, it is always a challenge to precisely measure the impact of specific formulation components on the collective performance attributes of the applied coating. In this work, the focus has been to develop novel techniques that can be used to demonstrate a more quantitative measure of some of the performance attributes that rheological additives like cellulose esters can provide to automotive coatings. A series of pigmented basecoat formulations were prepared which contained cellulose acetate butyrates (CABs) of varying molecular weights at different levels based on the total solids of the coating formulation. The nonvolatile content of the formulations was also varied. The viscoelastic behavior of a typical automotive basecoat formulation during the drying process was then investigated using a novel rheological technique. Complex viscosity data (including storage and loss moduli as well as tan delta) were determined as a function of drying time and then compared to the macroscopic properties typically associated with a coating film as it dries. Thermogravimetric analysis (TGA) was also used to correlate the rheology of the metallic basecoat formulations with drying behavior of the coating. The final appearance of the coating was investigated by several microscopic techniques such as Laser Scanning Confocal Microscopy, Scanning Electron Microscopy, Atomic Force Microscopy, and Surface Profilometery, and attempts were made to correlate bulk measurements like ‘flop index’ with the microstructure of the coating. Presented at the 2006 FutureCoat! conference, sponsored by the Federation of Societies for Coatings Technology, in New Orleans, LA, on November 1–3, 2006.     

Synthesis and characterization of interpenetrating networks from polycarbonate and cellulose acetate butyrate

Polycarbonates (PC) are currently used for organic optical glass; nevertheless they show a poor impact resistance which may be increased by combination with cellulose acetate butyrate (CAB) into a PC/CAB interpenetrating polymer network (IPN), without altering the material transparency as we show here. A series of rigid IPNs based on an aliphatic polycarbonate and CAB was prepared through in situ polymerization techniques. The kinetics of the formation of two networks in the IPNs were studied by FTIR spectroscopy. Effects of the CAB cross-linking and weight proportions of the two components in the IPNs were investigated by dynamic mechanical thermal analysis.     

Morphological development of polypropylene in immiscible blends with cellulose acetate butyrate

Isotactic polypropylenes (iPP) with different melt flow indexes were melt blended with cellulose acetate butyrate (CAB) and then prepared into microspheres or nanofibers following a novel process of producing well dispersed CAB/iPP immiscible blends and subsequent removal of the CAB matrix. The morphologies of iPP microspheres were investigated by a scanning electron microscopy, and the dimensions of iPP microspheres were evaluated. The melt viscosities of iPP, CAB, and CAB/iPP blends were measured by using a capillary rheometer. The influences of the viscosity, viscosity ratio, and composition ratio of iPP/CAB on the morphology formation of iPP in CAB matrix were studied.     

Star oligomers for low VOC polyurethane coatings

Conclusion  Hydroxyl functional star oligomers prepared by ring-opening polycondensation have a narrow molecular weight and composition distribution. Such oligomers give a solids/viscosity advantage over linear structures at the same molecular weight and can be used in low VOC two component polyurethane coatings. The solids/viscosity advantage is a combination of the highly branched structure and the narrow molecular weight distribution. Acrylic polyols formulated at the same molecular weight/polarity/average functionality and hydroxyl value give poorer drying properties. This difference can be explained by the fact that the free radical polymerisation technique leads to polymer compositions having a broad molecular weight and functionality distribution and high fractions of polymer with a low functionality. The potlife of acrylic polyols based formulations is adversely affected by the higher fractions of high molecular weight material and with a high average functionality. In low VOC polyurethane formulations star oligomers need to be formulated within a narrow range of compositions (TG, polarity), functionality and molecular weight to get an optimum balance of drying properties and potlife.     

Development of waterborne UV-A curable clear coat for car refinishes

The development of a waterborne UV-A curable clear coat for car refinish application is described. The clear coat formulations are based on specially developed acryloyl or maleimide functional polyurethane dispersions. The functional PUR dispersions are characterized by a relatively low molecular weight, a high CC functionality and an optimized amount of poly(ethylene oxide). These characteristics are necessary for obtaining optimal film formation which results in good appearance and other film properties. It was found that poly(ethylene oxide) had a positive effect on surface cure when irradiated with UV-A light (less influence of oxygen inhibition). The synthesis of PUR dispersions and their performance in clear coats are described, including several aspects on film formation (conversion of CC, AFM measurements) and film properties (durability, physical and chemical properties).     

Influences of polymer matrix melt viscosity and molecular weight on MWCNT agglomerate dispersion

In order to study the influence of melt viscosity and molecular weight on nanotube dispersion and electrical volume resistivity, three different polycarbonates (PCs) varying in molecular weight were melt compounded with 1 wt% multiwalled carbon nanotubes (MWCNTs, Baytubes^® 150 HP) using a small-scale compounder. The experiments were performed at constant melt temperature but at varying mixing speeds, thereby applying different magnitudes of shear stress. Light transmission microscopy was used to access the state of agglomerate dispersion, and electrical resistivities of the composites were measured on pressed plates. The results indicate that with increasing matrix viscosity the agglomerate dispersion gets better when using constant mixing conditions but worse considering comparable shear stress values. To study the effect of molecular weight, in a second set of experiments melt temperatures were adjusted so that all PCs had similar viscosity and mixing was performed at constant mixing speed. As investigated on two viscosity levels, the composites based on the low molecular weight matrix showed smaller sized un-dispersed primary agglomerates as compared to composites with higher molecular weight matrices, highlighting the role of matrix infiltration into primary nanotube agglomerates as the first step of dispersion. The resistivity values of composites prepared using low viscosity matrices were lower than those of composites from high viscosity matrix.     

CONCENTRATED ACID CONVERSION OF PINE SOFTWOOD TO SUGARS. PART I: USE OF A TWIN-SCREW REACTOR FOR HYDROLYSIS PRETREATMENT

The first stage of a two-step concentrated sulfuric acid process that converts softwood sawdust to sugars has been explored. The research focuses on the ability of an in-house custom fabricated corotating twin-screw reactor (TSR) to effectively break down and solubilize crystalline cellulose into low molecular weight carbohydrates. Based on design of experiment (DOE) screening results, a four-level, two-factor experimental model building DOE was undertaken. Solid sawdust conversion to liquid, screw torque, and TSR exit pressure were measured or recorded at each experimental condition to yield percent conversion of solids, processed material viscosity, and material energy requirements. Thereafter, model quadratic equations were fitted to the experimental data and found to be statistically significant. Based on data obtained in the DOE the process was optimized to establish a base case operating condition. The acid-treated product made at base case twin-screw operating conditions showed a 38.2% conversion of dry sawdust solids to soluble liquids. The dry solids conversion reduced 73.8% of all hemicellulose and 44.4% of all cellulose to soluble monomers and oligosaccharides.     

疏水缔合羟乙基纤维素的合成及性能表征

为改进羟乙基纤维素的溶液性能,通过羟乙基纤维素与长链溴代烷烃的大分子反应,制得疏水缔合羟乙基纤维素(BD-HAHEC);经由正交实验确定最优化工艺参数为:醚化剂∶羟乙基纤维素(质量比)=3∶10,活化剂浓度为4%,在80℃条件下反应5 h。用傅立叶红外光谱仪、粘度计和剪切流变仪对产品进行结构表征和性能测定,结果表明,与普通羟乙基纤维素相比,疏水改性羟乙基纤维素水溶液在增稠性、耐温耐盐性、抗剪切性等性能上均有明显提高;在相同反应条件下,由溴代十四烷改性的羟乙基纤维素具有比溴代十二烷改性更强的增稠性能。     

Light scattering studies on the ripening of viscose solution

Investigations were made on cellulose xanthate molecular weights by light scattering during the ripening of the solutions of (a) viscose-containing colored thio salts and (b) pure cellulose xanthate separated from viscose. Though an apparent reduction in molecular weight was recorded with time of ripening for the viscose solution, no such fall was observed with pure cellulose xanthate. The apparent fall of molecular weight in the case of viscose has been shown to be due to the increasing absorption of the incident beam and to the change in the value of dn/dc with progressive color formation. Reproducible results can be obtained for cellulose xanthate solutions freed from color. Intrinsic viscosity of the viscoses and the degree of polymerization (D.P.) of the regenerated cellulose from viscoses during ripening were also measured and found to be constant. The results indicate that no degradation of alkali cellulose molecule takes place during the ripening process, irrespective of the state of degradation of alkali cellulose from which the viscose is made.     

Hydrogels from polysaccharides. I. Cellulose beads for chromatographic support

Cellulosic hydrogels in bead form were prepared by dropwise addition of cellulose solutions in N,N-dimethylacetamide (DMAc) and lithium chloride (LiCl) to azeotropic methanol or isopropanol as nonsolvent. Bead properties were examined in relation to cellulose solution concentration, viscosity, and molecular weight. Bead properties were defined in terms of solids content, flow characteristics, mechanical strength, bead size, and pore dimensions. Results suggest that (a) beads can be prepared with solids content ranging from 2 to 12 wt %, depending on solution concentration; (b) uniform spherical shapes require a viscosity range between 100 and 300 cS: (c) beads can be produced in different sizes, within the diameter range of 100 to 1,500 μm; (d) linear flow velocities of packed bead columns are in the range of 70 to 350 cm/min; and (e) pore sizes of beads vary between 8 to 200 Å. Beads with low cellulose concentration show a wide fractionation range of up to 200,000 g/mol for polyethylene oxide. © 1996 John Wiley & Sons, Inc.     

Rheological Behavior of Injection-Moldable Silicon Powder–Silicon Carbide Whisker Formulations

The rheological behavior of injection-moldable formulations for reaction-bonded Si₃N₄ toughened with silicon carbide whiskers was studied using capillary rheometry. The effects on rheology of the following parameters were examined: solids loading, powder/whisker volume ratio, particle size and type, and binder composition. Two important aspects of the flow behavior were delineated. First, corrections for end effects and slippage along the wall were made in order to interpret the experimental data properly. At high shearing rates (i.e., 10³ s⁻¹) slip may account for more than 50% of the total flow. Such slippage promotes flow into the smallest channels or corners of the mold and may appreciably facilitate molding. Consequently the careful study of slippage is an inherent requirement of the rheological characterization of these concentrated suspensions. Second, the suspension viscosities were delineated. An empirical equation for predicting relative viscosity was developed for formulations containing up to ∼30 vol% of silicon carbide whiskers (with more than 50 vol% total solids). Suspension viscosities generally increased with decreasing particle size and increasing whisker contents. Particle surface roughness appears to affect the shearing behavior. Binders of low molecular weight resulted in higher relative viscosities than higher molecular weight binders, indicating possibly better dispersion of solids when more viscous binders are employed.     

Eco-friendly cellulose acetate butyrate/poly(butylene succinate) blends: crystallization,miscibility, thermostability,rheological and mechanical properties

In this work, the crystallization, miscibility, thermostability, rheological and mechanical properties of cellulose acetate butyrate (CAB)/poly(butylene succinate) (PBS) blends were investigated in detail. Differential scanning calorimetry analysis confirmed that PBS could form crystalline phase in the solution casted CAB/PBS blends with W_CAB?≤?60 wt.%. When the blends were crystallized from melt, the crystallization of PBS was found to be severely suppressed by the amorphous diluent of CAB. CAB and PBS were confirmed to be thermodynamic miscible in molten state by the negative value of Flory-Huggins interaction parameter (χ₁₂?=??0.89) between CAB and PBS. The rheological characterization results and thermogravimetric analysis revealed that the melt viscosity and thermostability of CAB were reduced and improved by blending CAB with PBS, respectively. Moreover, the rigid CAB became more flexible after incorporating with ductile PBS. The application of CAB is expected to be extended via blending the two species of eco-friendly polymers.     

High performance cellulose fibers regenerated from 1-butyl-3-methylimidazolium chloride solution: Effects of viscosity and molecular weight

In the present study, we focused on several factors affecting the utility of 1-butyl-3-methylimidazolium chloride (BMIMCl) for obtaining higher performance fibers. The dependence of the spinnability and tensile strength of the fibers on the zero-shear viscosity of the spinning solutions was investigated based on differences in the molecular weight of the cellulose, pulp concentration, and the pH of BMIMCl. We demonstrated an appropriate viscosity range of 2000–4000 Pa s⁻¹ (100 °C) for spinning dopes to obtain good spinnability and high tensile strength. The pH of the BMIMCl and the molecular weight of the cellulose clearly impacted tensile strength. The high molecular weight of cellulose contributed to high mechanical properties of the regenerated cellulose fibers. Optimizing the molecular weight and concentration of the cellulose based on the appropriate viscosity allowed us to prepare high performance cellulose fibers with a tensile strength of 1.15 GPa and a Young's modulus of 42.9 GPa. © 2019 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2019 , 137, 48681.     

Ternary polymer blends based on poly(lactic acid): Effect of stereo‐regularity and molecular weight

The effects of stereo‐regularity and molecular weight of poly(lactic acid) (PLA) on ternary polymer blends was analyzed using optical clarity as the primary screening method. This enabled the ready identification of phase boundaries of optically clear and apparently miscible regions. Solvent‐mediated blends of amorphous poly(dl ‐lactide) (PDLLA) and semi‐crystalline poly(l ‐lactide) (PLLA) with various molecular weights from high to low, along with polycaprolactone (PCL) and cellulose acetate butyrate (CAB) were used in this study. The nature and extent of crystallinity of the blends was examined by X‐ray diffraction, which, in conjunction with differential scanning calorimetry, scanning electron microscopy, and Fourier transform infrared spectroscopy, provided information about the competition between polymer crystallization (self‐aggregating behavior) and intermixing of the macromolecules. Thus, allowing the primary physical cause of transparency loss to be identified. The results of the ternary blends optical clarity showed the position of the phase boundaries in PLLA/PCL/CAB and PDLLA/PCL/CAB blends are significantly affected by the stereo‐regularity and molecular weight of PLA. The PDLLA (amorphous) blend shows comparable regions of phase separation with high molecular weight and semi‐crystalline PLLA blends even though the molecular weight is much lower. The blends of the shorter chain PLLA1 tend to show more crystalline regions. The optical transparency, miscibility, and crystallinity of the blends are not only affected by the stereo‐regularity and molecular weight of PLA but also the crystallizable PCL, especially at high loading. These findings give useful information to the film‐packaging sector where good optical clarity is a critical performance requirement. © 2014 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2015 , 132, 41780.     

Control of structure and mechanical properties for binary blends of poly(3‐hydroxybutyrate) and cellulose derivative

Structure and mechanical properties for binary blends composed of a poly(3‐hydroxybutyrate) (PHB) and a cellulose derivative, such as cellulose acetate propionate (CAP) and cellulose acetate butyrate (CAB), have been studied by means of dynamic mechanical analysis, isothermal crystallization measurements, and tensile testing. It is found that β relaxation temperature due to glass transition of PHB or PHB‐rich phase in the blends, in which the cellulose derivative has lower molecular weight, is almost the same as that of the pure PHB. On the other hand, the peak location is shifted to even lower temperature than that of the pure PHB by blending the cellulose derivative with higher molecular weight, although the cellulose derivative is a glassy polymer with high glass transition temperature. Further, the blend with lower β relaxation temperature exhibits ductile behavior with low modulus in uniaxial deformation. The difference in the structure and mechanical properties for the blends are found to be determined by the crystallization rate. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 103: 3447–3452, 2007     

Use of dielectric spectroscopy for real-time in-situ reaction monitoring

Coating resin manufacturing requires knowledge of the extent of reaction during resin synthesis so the appropriate actions can be taken (addition of the next reactant, reaction termination, etc.). This article reports the results from experiments conducted to survey the utility of dielectric spectroscopy (DES) as a real-time, in-situ technique to monitor the extent of reaction during synthesis of three low molecular weight resins that are representative of components used in coatings formulations. The resins made were based on very different chemistries: (1) a 100% solids polyacrylate functional oligomer from the Michael reaction between a polyacrylate monomer and an acetoacetate ester; (2) an acrylate functional monomer from the reaction between an epoxy ester and acrylic acid; and (3) a solvent-based isocyanate-terminated polyurethane prepolymer from the reaction between a mixture of diols and excess diisocyanate. In all three cases, very good to excellent correlations were found between continuous real-time DES output and the values of characteristic QC parameters (viscosity, acid number, epoxy equivalent weight, % NCO, ATR-FTIR peak heights for reactants and products, and GPC data) determined by off-line analysis of samples taken periodically during the reactions.     

Polysiloxane-Cellulose acetate butyrate cellulose interpenetrating polymers networks close to true IPNs on a large composition range. Part II

Interpenetrating polymer networks combining cellulose acetate butyrate (CAB) and α,ω-divinyl-polydimethylsiloxane (PDMS) in different weight proportions have been synthesized. The synthesis involves a one pot-one shot process in which all components are first mixed together. For each composition, the relative CAB and PDMS network formation rates are adjusted through the concentration of DBTDL used as CAB network formation catalyst. Thus, the chemically independent networks are formed quasi-simultaneously in order to avoid phase separation. The CAB cross-linking density effect on the PDMS/CAB IPN mechanical properties has also been particularly studied. All synthesized IPNs are transparent and only one mechanical relaxation temperature lying between those of the single CAB and PDMS networks is observed by DMTA analysis. These results show that the networks are correctly interpenetrated and no phase separation is observed at the DMTA level. Some mechanical properties of the PDMS network are significantly improved in this IPN combination and their stress-strain behavior has highlighted a synergistic effect arising from the IPN architecture. Thus, these IPNs exhibit many characteristics, which would allow defining them as close to ‘true’ IPNs.     

Viscosity ratio effects in the compounding of low viscosity,immiscible fluids into polymeric matrices

Many low viscosity, immiscible fluids are difficult to incorporate into polymer matrices because of thermodynamic immiscibility and a large mismatch of melt viscosities. In this investigation, a model system was used to determine the mechanisms and kinetics of mixing in such formulations. The model systems consisted of a series of different molecular weight polyethylenes in polystyrene. The viscosity ratio, η(polyethylene)/η(polystyrene), at 180°C and 100 s⁻¹ was varied from 0.7 to 0.003. Phase inversion was observed during the compounding of these formulations. The phase inversion was associated with a transition from low to high mixing torque during compounding. This change was primarily due to an increase in the blend viscosity caused by the morphological transformation. The melting behavior during compounding depended on the melt viscosity of the polyethylene. A critical viscosity ratio of ≈ 0.1 exists below which softening of the polystyrene, and thus mixing of the two components, was greatly retarded. Even at very low concentrations, low viscosity polyethylene can have a significant effect on the processing behavior. Effects of mixer set temperature, degree of fill, and polyethylene particle size were explored. The roles of thermal conduction and mechanical energy input were evaluated in the melting regime of the process.     

Preparation and evaluation of cellulose acetate butyrate and poly(ethylene oxide) blend microspheres for gastroretentive floating delivery of repaglinide

In this study, hollow microspheres of cellulose acetate butyrate (CAB) and poly(ethylene oxide) (PEO) were prepared by emulsion–solvent evaporation method. Repaglinide was successfully encapsulated into floating microspheres. Various formulations were prepared by varying the ratio of CAB and PEO, drug loading and concentration of poly(vinyl alcohol) (PVA) solution. Encapsulation of the drug up to 95% was achieved. The microspheres tend to float over the simulated gastric media for more than 10 h. The micromeritic properties of microspheres reveal the excellent flow and good packing properties. The % buoyancy of microspheres was found to be up to 87. SEM showed that microspheres have many pores on their surfaces. Particle size ranges from 159 to 601 μm. DSC and X‐RD revealed the amorphous dispersion in the polymer matrix. In vitro release experiments were performed in simulated gastric fluid. In vitro release studies indicated the dependence of release rate on the extent of drug loading and the amount of PEO in the microspheres; slow release was extended up to 12 h. The release data were fitted to an empirical equation to compute the diffusional exponent (n), which indicated that the release mechanism followed the non‐Fickian trend. © 2007 Wiley Periodicals, Inc. J Appl Polym Sci 2007     

Comparative Study of Effect of Surfactant-Polymer Interactions on Properties of Alkyl Polyglucosides and Alpha Olefin Sulphonate

The properties of Alpha Olefin Sulphonate (AOS) and Alkyl polyglucosides (APG) were studied in the presence and absence of nonionic polymers such as polyethylene glycol, poly vinyl pyrrolidone and methyl cellulose and hydroxy propyl cellulose. Properties like surface tension, foaming, viscosity and emulsification were studied at a constant concentration of polymer (0.1%) and varying concentrations of surfactant. It was found that at low surfactant concentrations there is an association between surfactant and polymer at the liquid/air surface in the case of an anionic surfactant and a nonionic polymer, which is not seen in the case of nonionic surfactants and nonionic polymers. A nonionic polymer reduces the surface tension of AOS by forming a surfactant-polymer complex which in turn increases the foamability, emulsifying property and viscosity of solution. APG does not show any effect on its surface tension in the presence of nonionic polymers but its foamability and emulsifying properties are improved. Reduction in surface tension is not the only reason behind increased foamability in the presence of the polymer. Higher molecular weight polymers give a rich, creamy foam because of increased viscosity in the surfactant solution as compared to lower molecular weight polymers.