Synthesis, thermal properties, and biodegradability of propyl-etherified starch

High amylose corn starch (HACS) was etherified with 1-bromopropane in dimethyl sulfoxide. The structure of the products was characterized by infra-red and ¹H-NMR spectroscopy. The degree of substitution (DS) on glucose unit calculated from ¹H-NMR spectrum was varied from 0.9 to 2.7 by changing feed ratio of 1-bromopropane to HACS. Thermogravimetric analysis reveals that the etherified HACS has a higher decomposition temperature than unmodified HACS. Differential scanning calorimetry analysis reveals that the etherified starch has a clear glass transition temperature which decreased with increasing DS, and that no melting point is observed. This result demonstrates that the etherified HACS mainly consists of amorphous region. The biodegradation rate decreases with increasing degree of etherification.     

Thermal properties of lignin-and molasses-based polyurethane foams

Lignin-and molasses-based polyurethane (PU) foams with various lignin/molasses mixing ratios were prepared. The hydroxyl group in molasses and lignin is used as the reaction site and PU foams with various isocyanate (NCO)/the hydroxyl group (OH) ratios were obtained. Thermal properties of PU foams were investigated by differential scanning calorimetry (DSC), thermogravimetry (TG) and thermal conductivity measurement. Glass transition temperature (T _g) was observed depending on NCO/OH ratio in a temperature range from ca. 80 to 120°C and thermal decomposition temperature (T _d) from ca. 280 to 295°C. Mixing ratio of molasses and lignin polyol scarcely affected the T _g and T _d. Thermal conductivity of PU foams was in a range from 0.030 to 0.040 Wm⁻¹ K⁻¹ depending on mixing ratio of lignin and molasses.     

Network structure and glass transition of epoxy resins cured with active ester

The effect of network structure on the glass transition temperature (T _g) was examined by differential scanning calorimetry, thermomechanical analysis and dynamic thermomechanometry for epoxy resins cured with mixtures of curing agents consisting of an active ester, 1,3,5-triacetoxybenzene (TAB), and a polyfunctional phenol, 1,3,5-trihydroxybenzene (THB). Free hydroxyl groups are formed from THB after curing, whereas acetyl groups are left from TAB. TheT _g value of cured epoxy resins decreased with increasing TAB content in the curing agent, which is attributed to the looser network structure induced by the steric hindrance of acetyl groups from TAB in the curing reaction and also to the weaker intermolecular interaction and the internal plasticization of acetyl groups from TAB.     

Novel cellulose derivatives. V. Synthesis and thermal properties of esters with trifluoroethoxy acetic acid

Esters of cellulose with trifluoroethoxy acetic acid (TFAA) were prepared in homogeneous phase using a mixed anhydride with p‐toluenesulfonic acid. Esters with low degree of substitution (DS), and with DS rising from 0 to 3, had hydrophobic character that prevented the usual association with moisture, which is otherwise typical of cellulose esters with low DS. Cellulose trifluoroethoxy acetate (CT) had T_g's declining by about 40 °C per DS‐unit (from 160 to 41 °C) as DS rose from 1 to 3. Mixed esters, cellulose derivatives with acetate and trifluoroethoxy acetate substituents (CAT), exhibited glass‐to‐rubber and melting transitions by DSC. A linear relationship between both T_g and T_m with respect to DS was recorded with the T_g and T_m separated by 30° to 40 °C. This is consistent with cellulose esters described elsewhere. Surprisingly, the T_g's of CT and CAT were found to be identical when the DS was equivalent to the DS of the fluoro substituents (DS_F). © 2000 John Wiley & Sons, Inc. J Polym Sci B: Polym Phys 38: 486–494, 2000     

The influence of chain length and branching on the glass transition temperature of some polyglucosans

Glass transition temperatures have been measured as a function of chain length for amylose acetate, amylose propionate and cellulose carbanilate derivatives using DSC and torsional braid techniques. Critical chain lengths could be predicted if the anhydroglucose ring was treated as a rigid unit in the amylose chain but as a more flexible entity in cellulose. The dependence of T_g on M^?1 was not predicted adequately by the Gibbs—DiMarzio theory over the complete molecular weight range. Branching was found to lower the glass transition temperature, but the effect was relatively small.     

“One pot” homogeneous synthesis of thermoplastic cellulose acetate-graft-poly(l-lactide) copolymers from unmodified cellulose

Using native cellulose as the starting material, cellulose acetate-graft-ploy (l-lactide) (CA-g-PLA) copolymers were successfully synthesized by “one-pot” process in an ionic liquid 1-allyl-3-methylimidazolium chloride (AmimCl). In this process, cellulose was first reacted with acetic anhydride, yielding cellulose acetate (CA), and then ring opening graft copolymerization of l-lactide was carried out from the residual hydroxyl groups of CA in the same solution using 4-dimethylaminopridine (DMAP) as the catalyst. Both acetyl and ploy (l-lactide) contents in CA-g-PLA copolymers could be well controlled by changing reaction conditions. The structures and thermal properties of CA-g-PLA copolymers were characterized. The glass transition temperature T_g of copolymers decreased with increasing PLA content. Compared to the pure PLA and cellulose-graft-PLA copolymers, the CA-g-PLA copolymers possessed better thermo mechanical properties in a temperature range of 60–130 °C. When the molar substitution of PLA (MS_PLA) was above 1.71, the CA-g-PLA copolymers exhibited thermoplastic behavior and could be processed by conventional thermal processing methods, such as injection molding and melt spinning.     

Novel cellulose derivatives. III. Thermal analysis of mixed esters with butyric and hexanoic acid

Cellulose derivatives with low degrees of substitution (i.e., DS < 1.5) often fail to reveal glass transition temperatures (T_g) by virtue of their tenacious adherence to moisture, thus preventing systematic analysis of substituent effects (size and DS) on T_g and T_m transitions. On the other hand, cellulose triesters have T_ms that decline with acyl substituent size except when the substituent size becomes very large (i.e., > C₆), and they have T_gs within 5–20°C of their T_ms. This proximity is unusual for a semicrystalline material, and it interferes with the crystallization process that occurs between T_m and T_g. Triesters of cellulose with mixed acyl substituents (one smaller and one larger) allow not only unambiguous observation of T_gs and T_ms but also an adjustable Δ(T_m ? T_g) window that depends upon the size and the DS of the larger substituent. The materials studied including cellulose acetate butyrate triesters (DS_bu 0.8–2.6), cellulose acetate hexanoate triesters (DS_hex 0–3.0), and cellulose acetate (DS_ac 2.44), revealed that only the mixed esters, in which the bulkier acyl group is in the range of DS 0.3–1.0, had a Δ(T_m ? T_g) value in excess of 40°C. Although the T_m of cellulose acetate hexanoate declined by ca. 150°C per unit of DS_hex as DS_hex rose from 0 to 1, this was only ca. 25°C between DS_hex of 1 and 3. Frequently observed dual-melt endotherms were attributed to two separate crystal morphologies. ©1995 John Wiley & Sons, Inc.     

Fabrication and characterization of transparent and biodegradable cellulose/poly (vinyl alcohol) blend films using an ionic liquid

Biodegradable blends were prepared from cellulose and poly (vinyl alcohol) (PVA) using the ionic liquid (IL) solvent, 1-butyl-3-methylimidazolium chloride. The blends were regenerated into films, fibers and rectangular blocks. The films showed optical transparency throughout the entire composition of the blends. The infrared spectroscopic experiments proved the existence of intermolecular hydrogen bonding interactions between the hydroxyl groups of cellulose and PVA. The miscibility between cellulose and PVA lead to increase in glass transition temperature (T _g) and of decrease in crystallinity of the blends. The T _g-composition data showed a negative deviation from Fox predictions, however fit well with BCKV model. The addition of PVA improved the tensile strength and elongation at break, considerably plasticizing cellulose. The blends can be degraded completely in soil. Moreover, the IL was completely recycled with high yield after the processing.     

Copolymers of dicyclopentadiene and tricyclopentadiene

Series of copolymers of dicyclopentadiene and tricyclopentadiene have been prepared by ringopening metathesis polymerization (ROMP) using a catalytic system of [W(=N-phenyl) (2,6-dimethyl phenolate)₄]/n-BuLi. Due to the presence of double bonds, the polymers obtained from ROMP are unstable. Thus the hydrogenation reaction is carried out after ROMP using a catalyst of bis(2,4-pentanediono)nickel/triisobutylaluminium. The polymers obtained were characterized by means of ¹H NMR; the results show an agreement with the proposed structure. Glass transition temperature T _g of the polymers are modulated by the feed mole ratio of dicyclopentadiene and tricyclopentadiene. With the increasing of tricyclopentadiene content, the T _g of the polymers before hydrogenation increases from 153 to 256°C, and the T _g of the polymers after hydrogenation increases from 106 to 188°C. In addition, the different ratio of dicyclopentadiene and tricyclopentadiene in polymer main chains offers different packing patterns to the structure of the copolymers, and leads to their different free volumes and occupied volumes.     

Two-step preparation and thermal characterization of cationic 2-hydroxypropyltrimethylammonium chloride hemicellulose polymers from sugarcane bagasse

Cationic sugarcane bagasse hemicellulose derivatives with a relatively low degree of substitution (0.01-0.54) containing quaternary ammonium groups were prepared by etherification with 3-chloro-2-hydroxypropyltrimethylammonium chloride or preferably with 2,3-epoxypropyltrimethylammonium chloride using sodium hydroxide as a catalyst in aqueous solution. The extent of etherification was measured by yield percentage and degree of substitution (DS). The DS values of the products could be controlled by adjusting the molar ratio of etherifying agent to anhydroxylose units in hemicelluloses and the molar ratio of sodium hydroxide to etherifying reagent. In comparison, the etherified hemicellulose preparations were characterized by both degradative methods such as thermal analysis, and non-degradative techniques such as gel permeation chromatography (GPC), Fourier transform infrared (FT-IR), and ¹³C nuclear magnetic resonance (NMR) spectroscopy. It was found that a significant degradation of the hemicellulose polymers occurred during etherification under the alkaline conditions used. The thermal stability of the etherified hemicelluloses was lower than that of the unmodified hemicellulose polymers.     

Thermal properties of freezing bound water restrained by sodium lignosulfonate-based polyurethane hydrogels

In order to develop a new functional product from lignin, sodium lignosulfonate (LS)-based polyurethane (LSPU) hydrogels were prepared from LS and hexamethylene diisocyanate (HDI) derivatives in water. Isocyanate/hydroxyl group ratio (NCO/OH ratio) was varied from 0.05 to 0.8 mol mol⁻¹, and water content (W_c = mass of water/mass of dry sample) of the obtained LSPU hydrogels was varied from 0 to 3.0 g g⁻¹. Phase transition behavior of hydrogels with various W_c’s was investigated by differential scanning calorimetry (DSC) and thermogravimetry (TG). In DSC heating curve of LSPU hydrogels, glass transition, cold crystallization, melting and liquid crystallization were observed. Cold crystallization, two melting peaks and variation of melting enthalpy indicate that three kinds of water, i.e., non-freezing water, freezing bound water and free water, exist in LSPU hydrogel. Glass transition temperature (T_g) decreased from 230 to 190 K in a W_c range where non-freezing water was formed in the hydrogel. T_g increased when freezing bound water was formed in the system. T_g leveled off in a W_c range where normal ice was formed. The effect of NCO/OH ratio on molecular motion of LSPU hydrogel is examined based on T_g and heat capacity difference at T_g (ΔC_p). Water vaporization curve measured by TG also indicates the presence of bound water which evaporates at a temperature higher than ca. 410 K. By atomic force microscopic observation, the size of molecular bundle of LSPU hydrogel is calculated and compared with that of LS-water system. By cross-linking, the height of molecular bundle decreased from ca. 3–1 nm and lignin molecules extend in a flat structure.

     

1‐allyloxy‐2‐hydroxy‐propyl‐starch: Synthesis and characterization

New reactive unsaturated starch derivatives, 1‐allyloxy‐2‐hydroxy‐propyl‐starches (AHP‐starches), were synthesized by the reaction of waxy maize starch (WMS) and amylose‐enriched maize starch (AEMS) with allyl glycidyl ether in a heterogeneous alkaline suspension containing NaOH and Na₂SO₄. The degree of substitution (DS) was determined by ¹H NMR spectroscopy, and a DS of 0.20 ± 0.01 was found for both AHP‐WMS and AHP‐AEMS, respectively. The AHP derivatives of WMS and AEMS were further characterized with ¹H and ¹³C NMR. It was shown that the AHP substitution was located on the C‐6 hydroxyl group of the glucose residues in the starch. The substitution pattern of the AHP groups along the polymer chain was randomly clustered, as determined by enzymatic digestion using pullulanase, α‐amylase, and amyloglucosidase, followed by matrix‐assisted laser desorption/ionization time‐of‐flight mass spectrometry analysis of the digestion products. With X‐ray diffraction and scanning electron microscopy, no changes in the granular morphology and crystallinity between the unmodified starches and AHP‐starches were detected. © 2007 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 45: 2734–2744, 2007     

Monitoring the formation of polystyrene/silica nanocomposites from vinyl triethoxysilane containing copolymers

Random copolymers of polystyrene-co-polyvinyl triethoxysilane (PS-co-PVTES) were prepared via semi-batch emulsion polymerization with different feed monomer compositions and evaluated as precursors of polystyrene (PS)/silica nanocomposites. Small-angle X-ray scattering (SAXS) profiles acquired from 20 °C to 180 °C showed that, at temperatures higher than glass transition temperature (T _g) of PS, the latex particles aggregate. On thermal annealing at 180 °C, silica-rich domains are formed, as corroborated by scanning electron microscopy. Infrared spectroscopy and differential scanning calorimetry analyses showed a reduction of the silanol concentration and an increase in the T _g value, respectively. The silica long domain spacing, measured by SAXS, depends on the concentration of vinyl triethoxysilane (VTES) in the feed; this value varied from 35 to 57 nm when the weight ratio of the monomers (styrene/VTES) was 50:50 and 90:10, respectively.     

Synthesis of hydroxyl‐bearing polyurethanes from naturally occurring myo‐inositol

A route from naturally occurring myo‐inositol to hydroxyl‐bearing polyurethanes has been developed. The diol prepared from the bis‐acetalization of myo‐inositol with 1,1‐dimethoxycyclohexane was reacted with a rigid diisocyanate, 1,3‐bis(isocyanatomethyl)cyclohexane to afford the corresponding polyurethane, of which glass transition temperature (T_g) was quite high as 192 °C. The polyurethane contains side chains inherited from the acetal moieties of the diol monomer and was treated with trifluoroacetic acid to hydrolyze the acetal moieties and afford the target polyurethane functionalized with hydroxyl groups. The presence of many hydroxyl groups in the side chains, which can form hydrogen bonds with each other, resulted in a high T_g, 186 °C. In addition, the hydroxyl groups were reacted with isocyanates to achieve further side‐chain modifications. © 2019 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2019, 57, 1358–1364     

Preparation of high‐temperature polyurethane by alloying with reactive polyamide

A series of novel poly(urethane amide) films were prepared by the reaction of a polyurethane (PU) prepolymer and a soluble polyamide (PA) containing aliphatic hydroxyl groups in the backbone. The PU prepolymer was prepared by the reaction of polyester polyol and 2,4‐tolylenediisocyanate and then was end‐capped with phenol. Soluble PA was prepared by the reaction of 1‐(m‐aminophenyl)‐2‐(p‐aminophenyl)ethanol and terephthaloyl chloride. The PU prepolymer and PA were blended, and the clear, transparent solutions were cast on glass substrates; this was followed by thermal treatments at various temperatures to produce reactions between the isocyanate group of the PU prepolymer and the hydroxyl group of PA. The opaque poly(urethane amide) films showed various properties, from those of plastics to those of elastomers, depending on the ratio of the PU and PA components. Dynamic mechanical analysis showed two glass‐transition temperatures (T_g's), a lower T_g due to the PU component and a higher T_g due to the PA component, suggesting that the two polymer components were phase‐separated. The rubbery plateau region of the storage modulus for the elastic films was maintained up to about 250 °C, which is considerably higher than for conventional PUs. Tensile measurements of the elastic films of 90/10 PU/PA showed that the elongation was as high as 347%. This indicated that the alloying of PU with PA containing aliphatic hydroxyl groups in the backbone improved the high‐temperature properties of PU and, therefore, enhanced the use temperature of PU. © 2002 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 40: 3497–3503, 2002     

Block/segmented polymers. A new method of synthesis of copoly(amide-ester)-ester polymer

A new method of preparation of segmented copolymer amide-ester type is described here starting from two oligomers, one hard crystallizable (A) having a glass transition temperature (T_g) above room temperature and the other soft, amorphous (B) having T_g well below room temperature. A, an oligo amide-ester terminated with hydroxyl groups has been synthesized from bis(hydroxy acylo amide) alkane, a reaction product of a lactone and diamine and dicarboxylic acid. B, an oligoester hydroxyl terminated was synthesized by the conventional method. The two oligomers A and B were transesterified removing diol as by-product to obtain segmented (amide-ester)-ester copolymer. The polymer showed mostly two T_gs one at ?40 to ?50°C and other at +40 to +50°C; and one melting temperature 200°C. Max^m inherent viscosity was recorded at 1.75 dL/gm. © 1993 John Wiley & Sons, Inc.     

Carbon nanotube–polyurethane shape memory nanocomposites with low trigger temperature

Ester-based polyurethane (PU) with low glass transition temperature was used to develop shape memory nanocomposites with low trigger temperature. Pristine carbon nanotubes (CNTs) and oxidized CNTs (ox-CNTs) were introduced by melt mixing to improve the mechanical and shape memory properties of the PU matrix. The dispersion of CNTs on the mechanical properties and shape memory behaviors of the nanocomposites were also investigated. The results show that better dispersion of ox-CNTs contributes to more stiffness effect below glass transition temperature (T_g) while lower storage modulus (E′) above T_g. The nanocomposites exhibit high shape fixity and recovery ratio above 98%. The ox-CNT/PU nanocomposite shows higher shape recovery ratio for the first cycle, faster recovery due to better dispersion of CNTs and have potential applications for controlling tags or proof marks in the area of frozen food. The trigger temperature can be tailored by controlling the T_g of the PU matrix or the content of the nanofillers.     

Glass transitions in starch,gluten and bread as measured

Dielectric Spectroscopy (DS) and Thermomechanical Analysis (TMA) were used to identity the glass transition temperature (T _g) of native wheat starch, vital wheat gluten and a commercial bread, in response to changes in moisture content. An open-ended coaxial probe technique was used to measure the permittivity or dielectric constant (?′) and the loss factor (?″) as functions of moisture, for 2.45 GHz frequency, at constant density and temperature. Plots of ?′ and ?″ as functions of moisture content showed dramatic changes in mobility-based dielectric properties, which occur upon transition from the glassy solid to the rubbery liquid state. The modified TMA method can measure the change in viscoelastic properties aroundT _g. This study further confirms that synthetic polymer science principles can be applied to food systems.     

Analysis of packing factors of crystalline polymers in terms of the glass transition to melting temperature radio

An expression for the ratio of the glass transition temperature to the melting temperature, T _g/T _m, was derived with allowance for fluctuations of the packing factor in the amorphous state. This relationship made it possible to describe the actual range of variation in T _g/T _m depending on a change in the packing factor in the crystalline state k _{o, cr}. The proposed approach forms the basis for the method of determination of increments in the packing ratio k _{o, cr} and formulation of the principles of selection of experimental data for calculations. The glass transition temperatures in polyethylene depending on the type of unit cell were calculated.