Shear rate and wall slip velocity functions of polyvinyl chloride melts based on slit die viscometry data

Shear stress versus shear rate and wall shear stress versus slip velocity relations of polymer melts are key material property functions needed in the design of polymer processing equipment. These properties are normally measured using capillary or slit viscometers. The presence of slip greatly complicates the processing of the resulting viscometry data. This paper describes the conversion of the viscometry data of a number of polyvinyl chloride melts through slit dies with different gaps into these two material property functions. The conversion procedure, based on Tikhonov regularization, has the advantage that it is independent of rheological constitutive equation and does not require extrapolation of the experimental data. It also has the ability to cope with the unavoidable noise in the experimental data. Consequently, the property functions thus obtained are likely to be closer to true material properties than those from some of the existing methods. For each of the polyvinyl chloride melts investigated, these properties' functions will be compared with published results and their differences discussed.     

Synthesis,properties, and applications of polylactic acid-based polymers

Polylactic acid (PLA) is known as one of the greatest promising bioabsorbable and compostable polyesters with the capability of high molecular weight synthesis. Lactic acid condensation, azeotropic dehydration, and condensation ring-open polymerize of lactide are three methods for PLA polymerization. Comprehension of material properties is critical for choosing the right processing method and adjusting PLA characteristics. A variety of mechanical properties of this material, from soft and elastic to stiff and high strength makes PLA suitable for a wide range of applications. Besides, PLA can be blended or copolymerized with other polymeric or non-polymeric substances. Thus, this polymer can achieve suitable chemical, mechanical, and rheological properties. Understanding the role of these properties and selecting a suitable processing technique is necessary for its intended consumer and various applications. This study elaborated a general summary of the polymerization, processing, and characteristics of PLA (i.e., structural diversities, rheological performances, mechanical properties, and permeability). Besides, this work presented some information regarding essential factors that can be used for modifying PLA properties to address the requirements for various applications such as biomedical, food packing, biocomposite, and additive manufacturing.     

Structure-property relationships of controlled epoxy networks with quantified levels of excess epoxy etherification

Epoxy thermosets are commonly formulated with an excess of epoxy resin to ensure complete reaction of co-reactive hardeners and to optimize performance. However, the degree to which the reaction of the excess epoxy resin contributes to the thermal and mechanical properties of the thermoset is incompletely understood. In this report, the preparation of controlled epoxy thermosets containing varying amounts of excess epoxy resin having essentially complete excess epoxy conversion is described. The extent of conversion was determined using a solid-state ¹³C NMR method with enhanced resolution due to solvent swelling of the thermosets. This etherification reaction increases the crosslink density of the epoxy thermosets but uniquely affects the thermal and mechanical properties of the materials. Significant property differences observed with respect to analogous thermosets made by varying crosslink density using different extender/hardener ratios are the sensitivity of T_g to the crosslink density and enhanced fracture toughness and tensile yielding with reduced bulk density.     

Rheological behavior of shear degradable oils: Kinetic and equilibrium properties

An investigation of the non-Newtonian, time dependent, flow properties of various crude oils at or below their pour points is reported. Experimental observations of material response under various shear and stress conditions provide a basis for the development of a kinetic and rheological model which quantitatively describes the shear degradation and equilibrium behavior exhibited by these materials. Preliminary data on the effects of thermal history and aging are also reported, showing the relative importance of these factors to the rheological properties.     

“In Water” Fabricated and Recycled Covalent Adaptable Acylhydrazone Thermosets

Thermosetting resins play an increasingly important role in daily life due to their good mechanical properties. However, they can hardly be recycled and reused, leading to severe environmental pollution. A very promising solution to this dilemma is to develop sustainable thermosets from biomass that can be recycled and reprocessed on demand under environmentally friendly conditions. In this study, sustainable thermosets based on dynamic acylhydrazone bonds made from biomass acid derivatives is reported. The sustainability of the presented acylhydrazone biomass covalent adaptable networks (CANs) thermosetting resins is summarized as follows: 1) The raw materials are renewable resources; 2) the resins can be recycled to maintain their mechanical properties, which can considerably extend their service life; and 3) the material preparation and recycling can be conducted in the mixed solvent of water/ dimethyl sulfoxide (7/3), which excellent reduced the use of organic solvents. In addition, these acylhydrazone CANs thermosets have excellent mechanical performance and outstanding heat resistance. The acylhydrazone bonds in the thermoset networks can enhance the hydrophobicity and water resistance of the acylhydrazone CANs thermosets. Taken together, these acylhydrazone CANs thermosets which are fabricated and recycled in the mixed solvent provide a solution to developing sustainable materials.     

Highly efficient in situ toughening of epoxy thermosets with reactive hyperbranched polyurethane

Hyperbranched polyurethane (HBPU), with low‐molecular‐weight polyethylene glycol space segments between the branching points, was synthesized by a pseudo one‐pot procedure. HBPU was characterized by Fourier transform infrared spectroscopy, nuclear magnetic resonance spectroscopy, and gel permeation chromatography. The HBPU was used as a modifier of diglycidyl ether of bisphenol A (DGEBA)/anhydride system. The rheological properties of HBPU‐G3/DGEBA blends were investigated by rotational rheometer. A slight decrease in viscosity of modified blends was observed by adding low content of HBPU and there was chemical reaction between HBPU and epoxy resin even without a hardener. The mechanical and thermal properties of the HBPU‐G3/DGEBA thermosets were characterized and compared with that of the neat epoxy thermosets. Their impact fracture surfaces were investigated by scanning electron microscopy, and the results indicated that no phase separation occurred in the DGEBA/anhydride system after the introduction of HBPU, which was confirmed by dynamic mechanical analysis and thermogravimetric analysis. After addition of 10 wt % HBPU, the toughness of the modified thermosets was found to be significantly improved without sacrificing their processability and thermal and mechanical properties to a large extent. © 2014 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2014 , 131, 40614.     

Synthesis of epoxy-terminated fluoropolymer via ATRP and the properties of epoxy thermosets modified with it

A novel fluoropolymer of epoxy-terminated poly(2,2,3,4,4,4-hexafluorobutyl methacrylate) (E-PHFMA) was synthesized and incorporated into epoxy resin to prepare thermosets. Gel permeation chromatography and ¹H nuclear magnetic resonance data obtained verified the synthesis and measured the structure of the polymer. In order to demonstrate the effect of epoxy group on the properties of the thermosets, the corresponding fluoropolymer without epoxy group was prepared and the properties of thermosets modified by two kinds of fluoropolymers were comparatively studied. The contact angle measurements indicated that the thermosets modified with E-PHFMA had a little worse hydrophobicity but better surface stability. Scanning electron microscopy revealed the surface morphologies of the modified thermosets before or after surface stability experiment. The results of differential scanning calorimetry and thermogravimetric analysis showed that the thermosets modified with E-PHFMA had higher thermal stability.     

高密度聚乙烯流变结晶性能对发泡的影响研究

采用差示扫描量热仪（DSC）和Hakke平板旋转流变仪测试了2种不同高密度聚乙烯（PE-HD）的热性能和动态流变性能,结合间歇发泡实验探究了PE-HD的发泡性能。结果表明,PE-HD的结晶速率以及黏弹特性对其发泡性能有明显地影响;HDPE6098具有适合发泡的流变特性和相对分子质量分布以及较快的结晶速率,可以获得发泡倍率为17.69倍,泡孔密度为1.30×10^6个/cm3的样品;而HDPE7000F由于高相对分子质量区域较大,模量较大,导致发泡过程中泡孔生长受到限制,获得的制品较差。     

Rheological characterization of fast-reacting thermosets through spiral flow experiments

The standard spiral flow test is normally used to assess the “moldability” of thermosetting materials. It is proposed that such tests can be modified and analyzed to yield rheological information as from a viscometer. Specifically, a “parameter-identification” scheme is developed to determine the constants in a viscosity model by minimizing the difference between the outcome of spiral flow tests and the results of numerical simulations of these tests. The proposed scheme is particularly applicable to fast-reacting thermosets for which typical viscometers cannot be used. Successful application of the scheme is demonstrated for a particular encapsulating epoxy material, where constants are obtained for a modified WLF equation viscosity model. These constants are used to predict the outcome of spiral flow experiments not involved in the minimization procedure. A favorable comparison between experiment and simulation occurs at most operating conditions. The method requires no elaborate equipment or delicate instrumentation.     

Dynamics of intumescence of fire-retardant polymeric materials

A new numerical method allowing one to estimate a temperature field in an intumescent fire-retardant coating is proposed. The data on heat conductivity of the material, on kinetics of its decomposition, and on kinetics of change of its rheological properties serve for calculation of input parameters. On the basis of experimental information about curing kinetics, the algorithm computes a viscosity of the material in each elementary layer of the coating. It is assumed that the local change of viscosity, in turn, predetermines a local expansion coefficient of the coating. The results of the calculations are compared with the experimental data obtained for the coating on the basis of phenol–formaldehyde resin and boron oxide. © 1998 John Wiley & Sons, Inc. J Appl Polym Sci 70: 1523–1542, 1998     

Heat distortion and mechanical properties of polymers by thermal-mechanical analysis

Polymer properties were measured as a function of temperature at 5 and 10°C per minute heating rates and as a function of time at constant temperature, using the Du Pont 940 thermal-mechanical analyzer. Data are reported on deflection temperature under load, vicat softening temperature, and creep properties. These results have been correlated with ASTM values. These tests require short times and are applicable to thermoplastics, thermosets, and elastomers.     

The effect of molecular weight distribution on polyethylene film properties

Polymer molecular weight heterogeneity affects the rheological properties of polymer melts such as melt viscosity, fracture and die swell. These rheological properties affect the conversion of the polymer from the bulk resin state to its final usable form. In this particular study, the effect of molecular weight distribution on polyethylene blown film characteristics was studied. The effect of the molecular weight heterogeneity on the rheological characteristics of the polymer in the molten state and its effect on the film properties is presented. The properties studied included film gloss, haze, tear resistance and film impact strength. This study shows that broadening the molecular weight distribution increases haze and reduces film gloss. Further, it was shown that a linear relationship exists between film gloss and external haze. Both values are measures of surface irregularities in the film which are affected by the drawing characteristics of the polymer. A broader molecular weight distribution results in increased impact strength as measured by the Dart Drop Impact Test. This is, it is believed, a result of the increase in long chain branching of the higher molecular weight fractions of the polymer which cause a higher degree of molecular weight entanglement at the branch sites. In contrast the tear strength is reduced as the molecular weight distribution broadens because of the low molecular weight fraction in the broad spectrum material which tend to decrease resistance to tear.     

Rheological behavior of polymer solutions during fabric coating

The overall performance of coated products is determined by the intrinsic material properties in solution and processing conditions. To characterize the behavior of these materials, the viscosity of polymers in solution at various concentrations was measured and the experimental data were fitted with the Carreau model. The results describe the rheological behavior of coating materials, and provide a basis for the modeling of polymer flow during the coating process. © 2007 Wiley Periodicals, Inc. J Appl Polym Sci, 2008     

The behavior of thermosetting compounds in injection molding cavities

The thermo-mechanical history of thermosetting compounds in injection molding cavities influences the ultimate properties of molded articles and affects both moldability and the productivity of the process. Mathematical modeling is an attractive approach for obtaining information regarding the thermo-mechanical history of the compound in the cavity. In order to obtain useful mathematical models of the thermoset injection molding process, it is necessary to have information regarding the kinetics and heats of reaction during cure; the rheological, thermal, and PVT properties of the thermosetting compound; and the variation of these properties with operating variables and the degree of cure. The paper outlines a model of the thermoset injection molding process in simple rectangular or semi-circular cavities. Methods are described for the experimental determination of the various physical and chemical properties of thermosets, which are required for modeling purposes. The results obtained in conjunction with the characterization of an epoxy system are illustrated. Finally, the paper demonstrates the results of mathematical modeling of the injection molding process for a commercial epoxy molding compound in a semi-circular cavity, and shows that reasonable agreement is obtained between model predictions and experimental data.     

Carborane‐incorporated poly(silyleneethynylenephenyleneethynylene)s with different side groups

Carborane‐incorporated poly(silyleneethynylenephenyleneethynylene)s with different side groups were synthesized from corresponding poly(silyleneethynylenephenyleneethynylene)s and decaborane (B₁₀H₁₄) in the presence of acetonitrile through in‐situ reaction. The obtained polymers with o‐carborane units were characterized by using Fourier transform infrared and nuclear magnetic resonance spectroscopies, rheological measurements, differential scanning calorimetry, and thermogravimetric analysis. The results show that the properties of these carborane‐incorporated polymers vary with side groups in main chains. They possess good processability and can be crosslinked to form thermosets at temperatures less than 250°C. The thermosets exhibit excellent thermal and thermooxidative stabilities. The weight losses of the thermosets heated to 800°C in air are only 10% approximately. After pyrolysis of the thermosets in nitrogen at 1000°C, the pyrolytic products have no further weight losses up to 1000°C in air. POLYM. ENG. SCI., 2012. © 2012 Society of Plastics Engineers     

The effect of chain packing on the thermal and dynamic mechanical behaviour of liquid‐crystalline epoxy thermosets

Liquid‐crystalline thermosets (LCTs) have received considerable attention since they exhibit many interesting properties. However, some aspects concerning LCTs are still unexplored. In particular, the structure–property relationships, as far as the organization of liquid‐crystalline (LC) domains in cured thermosets is concerned, have not been fully elucidated yet. We investigated the effect of the presence of a nematic mesophase on the thermal and dynamic mechanical behaviour of p‐(2,3‐epoxypropoxy)phenyl‐p‐(2,3‐epoxypropoxy)benzoate cured with 2,4‐diaminotoluene. Fourier transform infrared spectral analysis showed that epoxy group conversion was complete in both LC and isotropic (ISO) systems; moreover, a greater amount of intermolecular hydrogen bonding in the LC material was found. Thermogravimetric analysis evidenced similar thermal stability for the two systems, but a kinetic analysis of the data showed that the degradation process is more complex for the LC sample, and is characterized by higher activation energy. Dynamic mechanical thermal analysis (DMTA) showed lower glass transition temperature values for the LC system. Solid‐state NMR analysis evidenced lower paramagnetic oxygen absorption for this system. DMTA results show that the ISO material possesses a larger number of physical crosslinks, which act as extra constraints on the molecular motions. In the case of the LCT, the formation of a locally more dense structure is postulated, where the presence of more extended macromolecular segments leads to a smaller number of physical crosslinks, as also confirmed by solid‐state NMR analysis. A more compact molecular packing also leads to an increase of the activation energies of the thermal degradation process of the LC system. Copyright © 2010 Society of Chemical Industry     

石蜡/水相变乳液的制备与性能

低温石蜡/水相变乳液作为一种潜热蓄冷流体,具有储能密度高、可泵送的特点,可取代水作为传热介质应用于集中供冷系统中,降低二次循环水泵的运行能耗。基于集中供冷系统的应用要求,选择不同的组分制备相变乳液,包括石蜡、表面活性剂以及晶核剂,并研究其组分含量对乳液分散相粒径分布、热力学性能与流变性能的影响,最终确定相变乳液的制备方法与性能参数。采用所述方法制备的相变乳液具有良好的稳定性,其储能容量为水的2～6倍,且过冷度不高于2 K。     

3D打印混凝土材料可打印性的影响因素与测试方法

混凝土3D打印作为近年来发展出的高新技术,受到了广泛的关注,并取得了许多研究成果,但目前对材料特性的测试方法没有形成统一的认识.本文从流动性、凝结时间、流变特性、可挤出性和可建造性五个方面综述了3D打印混凝土的研究进展.流动度试验可以用来快速筛选出不适合打印的材料.从长远来看,凝结时间短的材料更有潜力.流变特性可以定量...     

Thermoset characterization for moldability analysis

The injection molding of thermosetting compounds involves complex interactions between material parameters and molding conditions, on one hand, and moldability and the ultimate properties of molded parts, on the other hand. The main role of the molding variables may be related to their effects on the cure time and temperature and on the flow and thermal phenomena that affect orientation and residual stresses. These effects are manifested in the ultimate mechanical properties and shrinkage of the molded articles. Only scattered empirical data are available on the effects of material parameters, like the basic kinetic, thermal, rheological, and pressure-volume-temperature properties of thermosetting compounds. The lack of useful information in this area may be related to the unavailability of sufficient, satisfactory data on the above properties. This situation has also resulted in limitations on meaningful work towards the mathematical modelling of the molding process, which would be useful for the optimization of production rates and product quality. The paper summarizes the status of work in this area with emphasis on recent results relating to kinetic, thermal, and rheological characterization of thermosetting molding compounds.