Viscoelastic properties of extrusion cast sheets of natural and synthetic aliphatic polyesters

The objective of this study was to determine the viscoelastic properties of natural (starch and protein) blends and synthetic biodegradable aliphatic copolyester blends. Blends of natural and synthetic biodegradable poly(butylene succinate) were cast into sheets using a coathanger die and then subjected to stress relaxation and creep tests at various temperatures. The natural content was varied at 10%, 30%, and 50% by weight. In some formulations a small (5% by weight) amount of compatibilizer was added. The materials were blended using a twin screw‐extruder, pelletized, and sheeted using a coathanger die. The decay of stress upon the imposition of constant strain showed two regions, an exponential and power law; the stresses relaxed sharply at the initial stage and then decayed at a reduced rate for the duration of the experiment. The addition of compatibilizers increased the time required for the stress to relax compared to uncompatibilized blends of the same composition. Similarly, as the natural content increased the time taken to relax to a specified stress level decreased. Increased temperature enhanced the relaxation process. The initial strain of the creep curves was affected by the natural content; the higher the natural content, the lower the initial strain for the samples upon imposition of a constant stress. Similarly, the presence of compatibilizer in the blend reduced the initial strain for samples containing the same natural content. As the natural content of the blend decreases, the time required to attain the plateau compliance is reduced. The equilibrium compliance increased with temperature. These behaviors are described in terms of blend morphology. The empirical Struik and power law models can be used to fit the compliance data well. POLYM. ENG. SCI., 45:1452–1460, 2005. © 2005 Society of Plastics Engineers     

The stability of solutions in reactive monomers of crosslinkable polyesters containing bisacid A2

Earlier papers^1–6 have dealt with the synthesis and purification of bisacid A2; the preparation of unsaturated polyesters by cocondensing bisacid A2 with maleic anhydride in varying proportions in the presence or absence of phthalic anhydride as a further modifying acid, using propylene glycol as the polyesterification diol; the hardness and the thermal and mechanical properties of cast, cured resins and glass fiber-reinforced laminates; and the water and chemical resistance of the cured resins. This paper deals with the solution stability of the liquid resins prior to cure and, in particular, with the observed fact that solutions containing esters of bisacid A2 in sufficient quantity do not require the addition of stabilizers commonly needed for commercial polyesters in order to impart an acceptable shelf life to the liquid resins.     

Properties of extrusion cast sheets of blends of natural and aliphatic polyesters

Natural and synthetic polymers of various compositions were blended in a twin‐screw extruder. These blends were then sheeted into thin sheets with a coat hanger die attached to a single‐screw extruder. The natural content in the blend was varied between 5 and 50 wt %, and the mechanical and morphological properties of the blends were evaluated. At 50 wt % natural content, the tensile strength decreased to a third of that of the synthetic polymer. The use of a compatibilizer doubled the tensile strength for the 50 wt % natural content blend. The sheets displayed equal strengths in the machine and transverse direction. The tear strength decreased as the natural content increased, and the decrease was greater in the anhydride‐compatibilized blends than in the uncompatibilized blends. The blends displayed two distinct glass transitions, one for each component, indicating phase separation. The crystallinity of the blends decreased as the starch content increased. This result was confirmed by differential scanning calorimetry (DSC), which showed that the melting endotherm decreased as the starch content increased. Gel permeation chromatography (GPC) results showed that the peak position was at the same location irrespective of blend composition, indicating minimal degradation of starch moieties. The water absorption was diffusion controlled, with a sharp initial burst of water uptake. Scanning electron microscopy (SEM) showed melting of starch granules that formed a co‐continuous phase with the synthetic polyester. Increasing the natural content also increased the surface roughness of the sheets. © 2003 Wiley Periodicals, Inc. J Appl Polym Sci 90: 1545–1554, 2003     

Fully ordered copolyhydrazides based upon bisacid A2

The preparation of copolyhydrazides containing equimolar quantities of “bisacetyl A2” and terephthaloyl or isophthaloyl groups is described. The resulting copolymers were found to form clear colorless films which, when immersed in concentrated formic acid, softened but rehardened and turned white after subsequent immersion in water. The formic acid treatment did not bring about a morphological change from the amorphous to the crystalline state, but caused changes in the differential scanning calorimetry (DSC) traces which suggest that an α/β transformation had taken place. The possible nature of this transition is discussed. The results of tensile tests on cast film are given.     

Crosslinked polyesters from “bisacid A2.” The mechanical properties of glass fiber-reinforced laminates

This paper reports the flexural and tensile test results on glass fiber laminates prepared from solutions in styrene of polyesters containing bisacid A2 and from standard commercial liquid polyester resins. The results are compared with each other. Suggestions are made for differences in strength, modulus, and strain. The results are presented in tables which give a statistical evaluation of numerous tests in terms of mean, range, and standard deviation.     

Thermal and mechanical properties of cast polyurethane resin based on soybean oil

The soy polyols were prepared from epoxidation of soybean oil followed by ring opening of oxirane obtained by using methanol as the ring opener. Polyols of hydroxyl (OH) numbers ranging from 128 to 174 mg of KOH/g were obtained by the variation of epoxidation time of soybean oil. A novel cast polyurethane resin has been synthesized by these polyols and 2,4‐toluene diisocyanate. Swelling of networks in toluene showed that the sol fraction varies from 1.13 to 72.06%. The thermal and mechanical properties of cast resins were characterized by differential scanning calorimetry and thermogravimetric analysis. The results showed that the glass transition temperature increases with the increase of OH number and that the thermal stability of the resins was slightly decreased with the increasing OH number. The tensile strength at break increases with the increase of OH number. Polyols with OH number of 174 mg of KOH/g gave glassy polymers, whereas those below this value gave rubbers. © 2009 Wiley Periodicals, Inc. J Appl Polym Sci, 2009     

Effect of composition and polyesterification catalysts on the optical properties of cured polyesters

Unsaturated polyesters based on ethylene glycol have been synthesized using a variety of anhydride, saturated and unsaturated dicarboxylic acids and various catalysts. The structure of the polyesters and the effect of the different compositions on the colour of cured polyesters are studied by FTIR, DSC and colorimetry. The structure of cured polyesters greatly depends on the isomerization of maleic acid to fumaric acid during polyesterification. The colour of unsaturated polyesters cured with the most common curing system (MEKP as initiator and CoNp as accelerator) is firstly influenced by the curing accelerator CoNp via the d–d transitions of the transition metal cobalt. Secondly, the composition of the dicarboxylic acids and anhydride used in the polyesterification influences the colour of the polyesters which depends especially on the isomerization of maleic acid. The cured maleate polyesters have more unreacted double bonds and more polar structure because of the presence of carbonyl groups, compared to the corresponding fumarate polyesters, and this structure affects the colour. The residual catalysts from the polyesterification have minor influence on the colour of cured polyesters. Copyright © 2002 Society of Chemical Industry     

Polyesters from bisacid A2. Electrical properties of glass fiber laminates

The preparation and purification of bisacid A2, the preparation of crosslinkable polyesters from bisacid A2, and some of the properties of the resulting resins and laminates have been reported in earlier communications.^1–7 This paper reports the surface and volume resistivities of laminates according to B.S. 2782 as well as their dielectric loss and permittivity at 23°C over a frequency range of about 9 decades and discusses the significance of the results.     

Cured polyesters based upon bisacid A2: Water absorption,toluene resistance,and resistance to 5% aqueous HNO3 and NaOH

Earlier papers have described the preparation and purification of bisacid A2,^1,2 the preparation and cure of crosslinkable polyesters,³ the thermal properties of cast sheet,⁴ and the mechanical properties of glass fiber laminates⁵ which were made from reactants that included bisacid A2 in two series of cocondensates. The present paper details the water absorption and the long-term effects (up to 12 months) of toluene, 5% aq. HNO₃, and 5% aq. NaOH. The effects of the last two were found to be negligible, but the water absorption and the toluene resistance appeared to be capable of correlation with the known composition and the inferred structure of the copolyesters.     

A polyamide from bisacid A2 and p-phenylenediamine: Synthesis,properties, and fiber formation

The synthesis, characterization, and processing of a new polyamide which is formed from bisacid A2 and p-phenylenediamine are reported. The polymer is synthesized using low-temperature solution polycondensation methods. The conditions for producing high molecular weight polymer are described. The polymer produced is amorphous, but lower molecular weight varieties may be crystallized with a formic acid treatment. Differential scanning calorimetry indicates a transition in the range of 180–190°C. Mechanical properties of films are measured. Fibers have been produced by both melt and wet spinning.     

Further studies on polyamides from bisacid a2

Earlier work on the low temperature solution polyamidation of bisacid A2 has raised a number of structural problems. Work carried out more recently showed that the problem of apparent nonisostoichiometry could be reasonably satisfactorily explained. The present paper reports the synthesis and investigates the properties of a further series of polyamides based upon Bisacid A2. More importantly, however, a detailed characterization and evaluation of the new polymers with respect to their structures is presented. This enabled us to compare the various structures in the light of the experimental evidence provided by a number of analytical and spectroscopic techniques, solution behavior, molecular weight, and thermal, morphological, and mechanical properties. Some work was also done on the effect of incorporating a small amount of a trifunctional monomer into the polyamide system.     

Thermal and mechanical properties of plywood sheets based on polystyrene/silica nanocomposites and palm tree fibers

Plywood sheets based on wood plastic nanocomposites were prepared using palm tree fibers (PTF) filled in polystyrene (PS) nanocomposites. The nanocomposite sheets were prepared using free radical polymerization of styrene monomer containing 60 % PTF and different nanosilica concentrations. The effect of coupling agent on the adhesion between PTF and PS/SiO₂ nanocomposites and PTF was pronounced at low nanosilica concentrations. The results of the flexural strength, impact test, abrasion resistance, and water absorption were explained on the basis of the effect of coupling agent between PTF and nanocomposite resin.     

Unsaturated polyesters based on terephthalic acid: 4. Sequence distribution of crosslinks in styrene cured resins

The sequence distribution of the styrene crosslinks in a cured polyester formed from propylene glycol, terephthalic acid and maleic anhydride has been studied by ¹³C nuclear magnetic resonance and infrared spectroscopy. The n.m.r. method involved the degradation of the crosslinked polyester into a copolymer of styrene and fumaric acid and the interpretation of the peaks in the ¹³C spectrum, which arise from the quaternary phenyl carbon atoms in sequences of styrene units, by considering the ¹³C spectra of copolymer standards of styrene and diethyl fumarate. The crosslinking process was monitored directly by infra-red spectroscopy, and the distribution of sequence lengths of styrene units was then estimated by considering that crosslinking may be interpreted by a statistical treatment of copolymerization. Values of mol fractions of styrene units in sequences of monads, diads and triads determined by ¹³C n.m.r. and infra-red spectroscopy were in fair agreement.     

Syntheses and photoluminescence properties of UV photocrosslinkable polyesters based on fluorene

Suppression of the green emission for polyfluorene has been widely investigated and various methods have been explored. In the present work, the photocrosslinkable copolyesters based on ferulic acid and 9-hydroxy-9-fluorene-carboxylic acid with different monomer feed molar ratios were synthesized and photocrosslinking reactions were employed to make the copolyesters crosslinked. All the photoluminescence spectra of the polyesters prior to photocrosslinking peaked at 418 nm in chloroform with quantum efficiencies more than 0.65. After crosslinking, copolyester P2 showed better thermo-stability of photoluminescence than the conjugated poly(9,9-dihexylfluorene). This indicated that the crosslinking architecture could suppress the chain aggregation, thus improving the purity of blue emission.     

“Bishydrazid A2”: A new semiaromatic film and fiber-forming polymer based on bisacid A2

We report the preparation of the dihydrazide of bisacid A2 (“bisdihidrazide A2”). Its composition and structure have been verified by elemental analysis and by means of infrared and NMR spectra. This material was then converted into a polyhydrazide (“bishydrazid A2”) in an HCl-accepting solvent. The polymer was converted to fiber by wet spinning the dope obtained during the polycondensation reaction without prior neutralization or dilution. Film was cast from a solution of the precipitated and washed polymer which had an inherent viscosity of about 0.8; mechanical tests on the film—both before and after treatment with formic acid—were carried out. Differential scanning calorimetry showed an α/β transition comparable to that shown by bisacid A2 polyaramides and described in preceding papers^1,2. Wide-angle x-ray scattering showed that the polymer is amorphous. Scanning electron micrographs revealed the physical structure of wet-spun fiber and the probable mechanism of fiber formation by dope extrusion into a water bath.     

Structure and mechanical properties of thermoplastic polyurethane,based on hyperbranched polyesters

A series of hyperbranched polyurethane (HB‐PU) were synthesized using hyperbranched polyester as a precursor. Morphology of these HB‐PU films was investigated using atomic force microscopy and wide‐angle X‐ray diffraction; it's molecular dynamics was studied by dynamic mechanical analysis. FTIR studies showed that hard segments get more aggregated to form domains in the HB‐PU block copolymer as hard segment content increases. Such domain formation has a significant influence on the mechanical and thermomechanical properties of HB‐PU, such as maximum stress and elongation at break. Especially, maximum stress and elongation at break increased significantly at 25 wt % of hard segment content, and the highest loss tangent was observed at the same composition. Heat of crystallization as measured by differential scanning calorimetry is also dependent on the hard segment content, and the control of hard segment content in PU block copolymers is very important in determining their physical properties. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 102: 5266–5273, 2006     

Thermal properties of an epoxide resin cured with bicyclo Diels-Alder anhydride adducts

The thermal properties of polymers derived from resorcinol diglycidyl ether cured with several bicyclo Diels-Alder anhydride adducts have been investigated. Increased char yields and decreased rates of weight loss were observed for these systems as compared to polymers cured by Diels–Alder adducts from acyclic dienes. This is explained on the basis of a reverse Diels-Alder reaction which these bicyclo adducts undergo at lower temperatures than do adducts from acyclic dienes.     

Unsaturated polyesters based on bis(2-hydroxyethyl)terephthalate

A series of unsaturated polyesters based on bis(2-hydroxyethyl)terephthalate, ethylene glycol, propylene glycol, diethylene glycol, maleic anhydride and styrene were prepared. Properties of these castings were investigated and compared with those analogues based on dimethyl terephthalate or polyester oligomers formed by depolymerization of poly(ethylene terephthalate). It is found that properties of castings based on bis(2-hydroxyethyl)terephthalate are superior to those based on polyester oligomer. When compared with those based on dimethyl phthalate, the castings have higher hardness and heat distortion temperature, but lower tensile strength and elongation; other properties are very similar.