Engineering plastics from lignin. VII. Structure property relationships of poly(butadiene glycol)-containing polyurethane networks

Hydroxypropyl lignin-based thermosetting polyurethanes containing polybutadiene (PBD) glycol soft segments (M_n of 2800 g M^?1) were synthesized with excess hexamethylene diisocyanate (HDI) and tolylene diisocyanate (TDI) by solution casting. Miscibility of the glycol with the lignin derivative was found to be poor as expected, and phase separation between the two polyol components in polyurethanes was detected by thermal and mechanical analysis, and by electron microscopy. This study examines the effect of concentration of polybutadiene glycol on the thermal and mechanical properties of the polyurethanes. The two-phase network system displayed significantly different properties than either the poly(ethylene glycol)-containing polyurethanes or their soft segment-free counterparts described previously. Macrophase separation was observed at nearly all degrees of mixing and was found to affect thermal and mechanical properties. The glass transition temperature (T_g) of the lignin phase in the TDI-based networks increased with poly(butadiene glycol) content rising from 3.6 to 71.4% of polyurethane, and this was attributed to the employment of a constant diisocyanate weight fraction which gave rise to a variable NCO/OH ratio and crosslink density. Distinct phase separation was evidenced by scanning electron microscopy (SEM) at above 3.6 and 7.1% glycol content for HDI- and TDI-based films, respectively. The polyurethane films behaved like rubber-toughened lignin networks when PBD was the discrete phase, and like lignin-reinforced rubber when the lignin derivative was discrete. This behavior was evidenced by the Young's modulus decreasing from 2000 to 50 MPa and ultimate strain rising from 6 to greater than 150%, with soft segment content increasing from 0 to 71.4%.     

Engineering plastics from lignin. III. Structure property relationships in solution cast polyurethane films

Lignin-based polyurethane films were synthesized by solution casting from hydroxypropyl lignin derivatives and either an aliphatic or an aromatic isocyanate. Two lignins, kraft and steam explosion lignin, and two diisocyanates, hexamethylene diisocyanate (HDI) and tolylene diisocyanate (TDI), were chosen for the study. It was found necessary to use stoichiometric excess diisocyanate in the synthesis of the thermosetting polyurethanes. This part of the series addresses the effect of synthesis variables on film properties. The study examines the effect of lignin type, of diisocyanate type, and of composition in terms of NCO to OH stoichiometry on thermal and mechanical properties. Stoichiometric NCO-excess was found to cause a more significant increase in the glass transition temperature of TDI-based films than of films made with HDI. The films swelled less with increasing NCO/OH ratio. Use of aliphatic diisocyanate (HDI) resulted in films with lower moduli as compared to aromatic diisocyanate (TDI). Kraft-lignin-based polyurethanes had slightly inferior strength characteristics (Young's modulus and tensile strength) in comparison with those derived from steam explosion lignin. Variation in the NCO/OH stoichiometry had no noticeable effect on modulus or tensile strength, but did significantly influence glass transition temperature, swelling, and strain at break. It is observed that the properties of these thermosetting polyurethanes are very sensitive to their composition. The study illustrates that materials of satisfactory performance characteristics can be engineered by proper selection of synthesis variables and modification of network architecture.     

Reprocessing acrylonitrile–butadiene–styrene plastics: Structure–property relationships

Acrylonitrile–butadiene–styrene (ABS) plastics from computer equipment housings have been reprocessed, some under various conditions of temperatures and shearing rates and others for multiple numbers of cycles. Structural changes in these reprocessed materials were investigated by infrared spectroscopy (FTIR), gel permeation chromatography, and dynamic mechanical thermal analysis. Gas chromatography/mass spectrometry was used to analyze extracts from the ABS plastics. These studies were related to measurements of the mechanical properties of the reprocessed materials, and the fracture surfaces were examined using scanning electron microscopy. It was found that impact strength was much more significantly affected than tensile properties by reprocessing. Within the range of reprocessing parameters studied, temperature had a more significant effect than shear rate on mechanical properties. Significant reductions in impact strength and slight increases in stiffness and strength, particularly following reprocessing at the highest temperature of 270°C and multiple reprocessing, were linked to loss of small molecules (including lubricants), degradation (crosslinking and scission) of the rubber phase, and changes in the morphology seen in the fracture surfaces. POLYM. ENG. SCI., 47:120–130, 2007. © 2007 Society of Plastics Engineers     

Structure–property relationships for azo disperse dyes on polyurethane fibre

Using two series of monoazo disperse dyes, the relationships between the molecular structure of dye and its dyeing properties, such as adsorption behaviour, fastness properties and distribution on polyurethane–polyester blends, were thoroughly investigated. Correlation analysis of experiment data revealed that the partition coefficient between octanol and water (CLogP) is the main factor affecting dye sorption. A greater level of CLogP tends to have a greater isotherm coefficient and better rubbing and washing fastness on polyurethane fibre, as well as a greater distribution ratio between the components of the blend. The dye dipole moment is negatively correlated with various degrees of washing fastness. The dye with two terminal hydroxy groups exhibited notable sorption on the polyurethane component and has the largest partition ratio on polyurethane–polyester in the blend. Corresponding regression analysis equations were identified.     

Structure–property relationships of composite films

Coextruded multifilms of varying chemical composition and structure were studied by the dynamic mechanical technique. The films studied were two- and three-ply combinations of a polyimide (Kapton) and fluorinated ethylene–propylene copolymer (FEP) and four other two-ply polyethylene and modified polyethylene composites: low-density polyethylene (LDPE)–ionomer, rubber-modified high-density polyethylene (HDPE)–ionomer; ethylene–vinyl acetate (EVA) copolymer–LDPE, and EVA-modified HDPE–LDPE. The mechanical spectra of individual film components were also obtained at 110 Hz between ?120° and 120°C (220°C for the Kapton–FEP system). Mechanical relaxations were examined to determine the degree of interaction between adjacent films and correlate them with tensile and ultimate properties of the composite.     

Thermoplastic apparent interpenetrating polymer networks of polyurethane and styrene/acrylic acid block copolymer: Structure–property relationships

Thermoplastic apparent interpenetrating polymer networks (t‐AIPNs) of crystallizable polyurethane (CPU) and a styrene/acrylic acid block copolymer (S‐b‐AA, acid form) of several compositions were prepared by casting from a common solvent. A variety of experimental techniques, including size exclusion chromatography (SEC), differential scanning calorimetry (DSC), thermogravimetric analysis (TGA), dynamic mechanical analysis (DMA), broadband dielectric relaxation spectroscopy (DRS), thermally stimulated depolarization currents (TSDC), and density measurements were employed to investigate structure–property relationships of the t‐AIPNs. Special attention was paid to the investigation of molecular dynamics of the CPU component in the t‐AIPNs, by combination of the dielectric DRS and TSDC techniques, as well as from the methodological point of view, to the prospects of morphological characterization by broadband DRS. The results show that the CPU/S‐b‐AA t‐AIPNs studied can be considered as multiphase systems having at least two amorphous and one crystalline phases, as well as regions of mixed compositions. Their properties are determined by the heterogeneity of the individual components, as well as by the heterogeneity caused by the thermodynamic incompatibility of these components. The degree of incompatibility is determined, to a large extent, by the intermolecular hydrogen bonding between the functional groups of the CPU and the S‐b‐AA components (ester groups and COOH‐groups, respectively), which is more effective on addition of small amounts of either of the components. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 101: 1021–1035, 2006     

Structure–property relationships in thermoplastic‐apparent interpenetrating polymer networks based on crystallizable polyurethane and styrene–acrylic acid copolymer

Structure–property relationships in thermoplastic‐apparent interpenetrating polymer networks (t‐AIPNs), prepared by mechanical blending in a common solvent of crystallizable polyurethane (CPU) and styrene/acrylic acid random copolymer (S/AA), were investigated by means of wide‐angle and small‐angle X‐ray scattering (WAXS and SAXS), dynamic mechanical analysis (DMA), thermally stimulated depolarization currents (TSDC) techniques, dielectric relaxation spectroscopy (DRS), and density, water uptake, deformation, and strength characteristics measurements. Several mechanical and dielectric relaxations of the pure components were characterized, and the effects thereupon induced by blending were followed. The two components show weak affinity to each other. The t‐AIPNs can be classified into two groups with high and low contents of CPU, showing essentially the behavior of CPU and of S/AA, respectively. On the other hand, deviations from additivity in several properties indicate interactions between the two components, caused by the formation of H‐bonds between their functional groups, and resulting in partial miscibility. In addition, significant changes are observed on some properties of the t‐AIPNs on addition of small amounts of either of the components. © 1999 John Wiley & Sons, Inc. J Appl Polym Sci 73: 385–397, 1999     

Structure–property relationships in crosslinked networks from cis-1,4-polybutadiene and methacrylic acid. Swelling behavior

In the present paper, we report results obtained analyzing the swelling behavior of a composite system prepared from vulcanizing mixtures of cis-polybutadiene and methacrylic acid with different amounts of acid. Two solvents were used as swelling agents, decalin and the N,N-dimethylformamide. The structural data, given by low-angle x-ray diffusion spectra, were used to interpret the mechanical behavior described in terms of the Mooney-Rivlin equation and hysteresis loops. Structural and mechanical data give information about the swelling mechanism of the solvents and about the problem of the experimental deviations from the Gaussian theory of rubber elasticity.     

Structure–property relationships in crosslinked networks from cis-1,4-polybutadiene and methacrylic acid. Preliminary results

In this paper we report preliminary results obtained analyzing structural data and mechanical properties of a composite system prepared vulcanizing mixtures of cis polybutadiene and methacrylic acid with different acid amount. The structure was investigated by the small angle x-ray scattering, while the physicomechanical properties were analyzed carrying out stress and birefringence measurements as function of the strain at constant temperature.     

Engineering plastics from lignin

Summary Low density polyurethane foams (ca. 2 lbs./cu. ft.) with acceptable strength and excellent flammability resistance properties were formulated with a commercial furan polyol containing 20% hydroxypropyl lignin derivative. Propylene oxide-modified lignin from two sources, kraft and organosolv lignin, were employed. The organosolv lignin derivative exhibited better foaming characteristics than the corresponding kraft lignin, which collapsed when the rising foam was touched for testing. The weight contribution of lignin derivative was limited to 20% by compatibility with the fluorocarbon blowing agent, and solubility in polyol. Preliminary tests encourage further research on structural materials containing hydroxypropyl lignin derivatives.     

Polyurethane ionomers. I. Structure–properties relationships of polyurethane ionomers

The influence of chemical structure on mechanical properties of polyurethane ionomers (PU ionomers) has been examined. NCO-terminated prepolymers prepared from primarily 4,4-methylene bis(phenyl isocyanate) (MDI) and poly(oxytetramethylene) glycol (PTMO) were chain extended with tertiary amine-containing diols and the ionomers obtained by quaternization of the prepolymers. The N-methyldiethanolamine chain extender gave the best physical properties. The mechanical properties of the PU ionomers were improved with decreasing chain length of PTMO and with increasing concentration of quaternary ammonium centers (or NCO/OH ratio of PU prepolymers). A lower degree of quaternization resulted in a decrease in the mechanical properties of the resulting PU ionomers, but their properties could be improved by post-quaternization. The adhesion of the PU ionomers to aluminum and the glass transition temperature increased with increasing concentration of quaternizing centers.     

Structure–property relationships in PVC compression moldings

Compression moldings were produced from two rigid PVC compounds at a range of temperatures. The tensile and impact properties of these moldings depended primarily on the level of particle fusion as assessed by extrusion rheometry. Properties were not related to the level of primary crystallization measured by X-ray diffraction, but the particle fusion process appears to be at least partly due to recrystallization. Fusion occurred more readily in the mass PVC compound than in the suspension PVC compound. Annealing the sheet produced at 200°C caused changes in crystallinity which resulted in small property changes. The maximum annealing effect occurred at 110°C.     

Photosensitive polynorbornene based dielectric. I. Structure–property relationships

In the microelectronics industry, the drive for increasing device speed, level of functionality and shrinking size has placed significant demands on the performance characteristics of polymer dielectrics. In this study, a negative acting, photodefinable dielectric formulation based on a copolymer of decylnorborne (decylNB) and epoxynorbornene (AGENB) was investigated for use in electronics packaging. The structure–property relations of this copolymer were investigated. Copolymer composition and processing conditions were shown to significantly affect the properties of the final polymer films. A lower content of AGENB results in lower moisture absorption, dielectric constant, modulus and residual stress, but it compromises multilayer capability. High crosslink density lowers the dielectric constant but increases the modulus and residual stress. © 2004 Wiley Periodicals, Inc. J Appl Polym Sci 91: 3023–3030, 2004     

Engineering plastics from lignin. XVII. Effect of molecular weight on polyurethane film properties

A series of five fractions with number average molecular weights (M?_n) between 1500 and 10,000 daltons were isolated from a Kraft hydroxypropyl lignin (HPL). From ¹H-NMR and UV analysis the chemical properties of the HPLs were found to vary slightly with molecular weight. The hydroxyl content decreased while the glass transition temperature (T_g) increased as the HPL molecular weight increased. The Fox-Flory equation adequately described the M?_n vs. T_g relationship. The HPL fractions were used as polyols for the preparation of solvent-cast polyurethane networks (PU) in film form. The T_g of the PUs increased from 40° to 120°C as the M?_n of the polyol rose from 1500 to 10,000 daltons. The molecular weight between crosslinks (M?_c) of the networks was determined by swelling. An observed decrease in M?_c with an increase in M?_n was related to the functionality of the system. The strength properties of films prepared from fractionated HPLs were superior to those prepared from nonfractionated HPLs.     

Structure–property relationships of thermally bonded polypropylene nonwovens

The effect of fiber structure and morphology on the resultant mechanical and low load deformation properties of thermally bonded nonwoven polypropylene fabrics has been studied. Commercially available staple polypropylene fibers varying in linear density and draw ratio (Herculon and Marvess staple fibers) were used in this study. The orientation of these fibers was characterized by birefrigence measurements. Differential scanning calorimetry measurements were made to determine the heat of fusion and melting point of fibers. Experiments confirm that tensile strength and stiffness of the fabrics correlate with this fiber structure. Under the same bonding conditions fabrics made from fibers with low draw ratios show higher tensile strength and stiffness than do fibers with high draw ratios. The mechanical properties of fabrics were found to be greatly affected by the thermal bonding temperature. The tenacity and flexural rigidity of fabrics made from poorly oriented fibers show higher values than those made from highly oriented fibers. The shrinkage of the fabrics was observed to increase with increasing bonding temperature in both machine and cross machine directions. The changes in fabric thickness due to the thermal bonding are considerably lower for poorly oriented fibers.     

Structure–property relationships in some composite systems. Deformation mechanism

In the present paper, we report the photoelastic behavior of composite elastomeric systems. The samples were obtained by vulcanizing mixtures of cis-polybutadiene and a polar monomer. The polar monomer used was methacrylic acid or magnesium methacrylate. The photoelastic analysis was carried out on samples with different monomer amount and in different swelling conditions. This kind of analysis gives informations about the deformation mechanism of these systems.     

Engineering plastics from lignin. I. Synthesis of hydroxypropyl lignin

Hydroxypropylation of lignin in a batch reactor under alkaline conditions at 180°C was studied using propylene oxide (PO) by itself, and PO in combination with several ligninlike model compounds and with kraft lignin. While the PO homopolymerization rate increased rapidly at temperatures above 85°C, and was too fast to be determined accurately at 180°C, the addition of model compounds and lignin was found to delay homopolymerization in relation to the presence of ionizable functional groups. The observations are consistent with a reaction mechanism involving first order kinetics with regard to each alkoxide and PO concentrations. Where the reaction rates toward PO increase with increasing pK_a values, the reaction sequence proceeds in the order of declining basicity. Thus lignins with high acidity were found to be subject to greater degrees of modification than those with more neutral character. This explains the earlier observed beneficial effect of lignin carboxylation on the properties of lignin–PO reaction mixtures.     

Structure–physical property relationships in peroxide-cured butadiene–styrene copolymers

Structure–physical property relationships in high-vinyl butadiene–styrene copolymers have been determined for samples cured with dicumyl peroxide under the same conditions. Three different structures, butadiene–styrene–butadiene (B–S–B) triblocks, butadiene–styrene (B–S) diblocks, and random butadiene–styrene copolymers, have been examined. Flexural modulus increases with increasing styrene content owing to the inherent stiffness of a polystyrene backbone. Swelling increases whereas hardness and heat distortion temperature decrease with increasing styrene content. This behavior is explained by the decrease in crosslink density with increasing styrene content in all structures. Heat distortion temperatures of the B–S–B and B–S networks are superior to the heat distortion properties of the random structures. The B–S–B structure is the most solvent resistant, followed by the random copolymers, with the B–S structures swelling to the greatest extent. Swelling differences between the B–S–B and random networks decrease with increasing styrene content, while swelling differences between the B–S–B and B–S networks increase with increasing styrene content. These results are explained by the nature of the crosslinking reaction and the number of loose ends present in each network.     

Engineering plastics from lignin II. Characterization of hydroxyalkyl lignin derivatives

Several types of hydroxyalkyl lignin derivatives were synthesized from milled wood, organosolv, steam explosion, acid (H₂SO₄) hydrolysis, and kraft lignin with ethylene oxide, propylene oxide, and butylene oxide by either batch reaction in toluene at 180°C using KOH as catalyst, or in aqueous alkali at room temperature. The isolated derivatives were characterized in terms of their chemical structures by H-NMR and FT-IR spectroscopy. Thermal properties were determined by differential scanning calorimetry. Molecular weights were measured by gel permeation chromatography on polystyrene/lignin model compound calibrated high pressure μ-spherogel columns. Solubilities in various organic solvents spanning a solubility parameter (δ) range from 9.3 to 14.5 and a hydrogen bonding index (γ) range from 1.5 to 18.7 were tested using UV₂₈₀ absorption of solutions of up to with degrees of substitution of between 1 and 2.6 (except for ethylene oxide derivatives which were higher) and with lignin contents of around 60%. The drastic reduction of glass transition temperature of between 50° and 100° is explained with increased free volume of the copolymer and with disruption of hydrogen bonds involving especially phenolic hydroxy groups. The greatly enhanced solubility in organic solvents indicates absence of the gel structure typical of network polymers. No molecular breakdown was observed as a consequence of oxyalkylation. The derivatives had molecular weights (M_w) of between 2000 and 50,000 at dispersity factors of between 2.5 and 25. The derivatives seem to constitute useful prepolymers for thermosetting engineering plastics.     

Structure–property relationships of medium‐density polypropylene foams

This paper is focused on the production and characterization of a collection of polypropylene (PP) foams with relative densities ranging from 0.3 to 0.6. Samples were foamed using the improved compression moulding method. The process allows controlling density and cellular structure independently as well as obtaining PP foams without fillers, crosslinking or using special PP grades. The influence of blowing agent content, density, cellular structure and foaming conditions on the mechanical response measured in compression, tensile, bending and Charpy impact tests was determined. Results show that density, open cell content and blowing agent concentration have a significant influence on the mechanical performance of medium‐density PP foams. © 2013 Society of Chemical Industry