Effect of thermal history on properties of block-copolyetheresters with poly(tetramethylene 2,6-naphthalenedicarboxylate) segments

The effect of compression molding on the thermal transitions and crystalline properties of block-copolyetheresters with hard segments of poly(tetramethylene 2,6-naphthalenedicarboxylate) and soft segments of poly(tetramethylene oxide) were investigated by differential scanning calorimetry (DSC), X-ray diffraction, thermal stimulated current (TSC), and dynamic mechanical analysis (DMA). The X-ray diffraction patterns of compression molded samples of the block-copolymers were considerably different from those of the corresponding samples with slow-cooling history. After compression molding, the diffraction peaks were changed completely indicating a different crystalline structure for the polyester segments, and the diffraction peaks became sharper indicating a higher crystallinity. The DSC results also showed that the melting point and crystallinity of the polyester segments were increased after compression molding. The glass transition temperatures of the polyether soft phase and polyester hard phase also were determined by DSC, TSC, and DMA separately with consistent data and were found to be dependent on the content of polyether segments and the molecular weight of the poly(tetramethylene ether)glycol (PTMEG) used. A γ-transition was observed by TSC and DMA and seemed to be independent of the composition and the thermal history. The glass transition temperatures of the polyether soft phase and the polyester hard phase of the block-copolymers derived from PTMEG 650 and PTMEG 1000 shifted to a lower temperature after compression molding possibly because of the partial miscibility between the comprising segments in these two series. The abrupt drop in log G′ in the temperature range of −10–15°C for the block-copolymers derived from PTMEG 2000 was caused by the melting of the polyether segments and indicated that the crystalline properties of the polyether segments could affect their mechanical properties. © 1999 John Wiley & Sons, Inc. J Appl Polym Sci 73: 1441–1449, 1999     

Statistical evaluation of the effect of the mold temperature on the strength of glass containers

Using methods of mathematical statistics (cluster, dispersion, and correlation analyses), the impact strength of three types of glass containers (bottles and jars) was analyzed. Three temperature regions in which molding results in very different values of the strength of the articles are revealed. The boundaries of the molding temperature regions are critical regardless of the type of article molded and are probably only determined by the chemical composition of the glass melt. The preferred mold temperature range is 480–550°C. The results of the study are interpreted based on an analysis of the features of molding glass at different temperatures. __________ Translated from Steklo i Keramika, No. 2, pp. 3–7, February, 2007.     

Selecting the conditions of molding iron oxide catalysts for dehydrogenation

The effect of the conditions for molding iron oxide catalysts for dehydrogenation of iso-amylenes to isoprene on their operation characteristics was studied. The investigation of laboratory samples allowed us to determine the optimum molding pressure (200–250 MPa) under which high mechanical strength (strength factor K _G = 33.4–37.3 N/mm), the stability of the kinetic characteristics in the dehydrogenation reaction, and the formation of 15–50 nm pores, ensuring the occurrence of the process in the kinetic region, were attained. we propose using the extrudate density as an indirect criterion for estimating the molding pressure under industrial conditions of extrusion. It was shown that in order to develop high strength properties (K _G ∼ 29.1 N/mm) of the catalysts upon their production under industrial conditions and to ensure the occurrence of the reaction in the kinetic region, the extrudate density must be 2.40–2.46 g/cm³. The obtained results were verified via paste molding on various industrial extruders, thereby enabling us to recommend the type of molding extrusion equipment.     

Study on modified phenolic resin. II. Modification with p-hydroxyphenylmaleimide/styrene copolymer

The improvement of heat resistance and mechanical properties of phenolic resin was examined with the blend of novolac and copolymers prepared from p-hydroxyphenylmaleimide (HPMI) and styrene. Copolymers of HPMI and styrene with various molecular weights were synthesized. Glass transition (T_g) and thermal decomposition temperatures of the copolymers were measured by differential scanning calorimetry (DSC) and thermogravimetry (TG), respectively. The miscibility of the copolymers with novolac was examined by DSC. It was found that the copolymers had a good heat resistance and a good miscibility with novolac. Molding compounds were prepared by hot roll-kneading of mixtures that involved novolac, copolymer, hexamethylenetetramine (hexamine), and glass fiber. It was found that the test pieces prepared by transfer molding from the molding compounds showed a good heat resistance and better mechanical properties than phenolic resin modified with HPMI homopolymer.     

Cure behavior of an epoxy–novolac molding compound

The isothermal cure of an epoxy–novolac molding compound was studied by means of differential scanning calorimetry (DSC). The glass transition temperature (T_g) of the molding compound increased in an approximately linear manner with conversion (α) during the major part of the cure process. Predictions of an empirical kinetic scheme (established earlier from dynamic DSC results) compared favorably with the present isothermal results in the absence of vitrification. In combination with the gel point conversion (α_gel) determined via dynamic rheological analysis and gravimetric measurements, our DSC results indicated that gelation bears no apparent effect on the rate of cure whereas vitrification retards the cure reaction. Based on the measured α_gel, the approximate T_g?α relationship, and the thermokinetic results, the time–temperature–transformation diagram of this molding compound was constructed and discussed.     

Effect of microstructure tuning by rapid heat cycle molding on the photodegradation behavior of isotactic polypropylene

Rapid heat cycling molding (RHCM) is an injection molding technique that improves the product quality of isotactic polypropylene (iPP) by tuning the microstructure, but its effect on the photodegradation stability remains to be investigated. In this work, the effect of RHCM tuned microstructure on the photodegradation behavior of iPP was investigated and compared with conventional injection molding (CIM). Differential scanning calorimetry (DSC), x-ray diffraction (XRD), Fourier transform infrared spectrometer (FTIR), atomic force microscopy (AFM), and shore durometer (D scale) were used to examine the photodegradation behavior of iPP samples. The results showed that RHCM increased the crystallinity, crystal size, and β-crystal content of iPP samples. With the increase of photodegradation time, iPP samples injected with RHCM showed higher stability in terms of microstructure and surface quality. The relative changes in CI and R_a of RHCM90 were reduced by 48% and 40% after 800 h of UV irradiation, respectively. In addition, the combined results of dynamic mechanical analysis (DMA) and UV–visible absorption spectrum showed that RHCM promoted the development of crystalline structure and reduced the mobility of the surface chain segments as well as UV absorption coefficient. These combined effects contributed positively to its photodegradation stability.     

Studies on structural foam processing II. Bubble dynamics in foam injection molding

An experimental study was carried out to gain a better understanding of the dynamic behavior of gas bubbles during the structural foam injection molding operation. For the study, a rectangular mold cavity with glass windows on both sides was constructed, which permitted us to record on a movie film the dynamic behavior of gas bubbles in the mold cavity as a molten polymer containing inert gas was injected into it. The mold was designed so that either isothermal or nonisothermal injection molding could be carried out. Materials used were polystyrene, high-density polyethylene, and polycarbonate. As chemical blowing agents, sodium bicarbonate (which generates carbon dioxide), a proprietary hydrazide and 5-phenyl tetrazole, both generating nitrogen, were used. Injection pressure, injection melt temperature, and mold temperature were varied to investigate the kinetics of bubble growth (and collapse) during the foam injection molding operation. It was found that the processing variables (e.g., the mold temperature, the injection pressure, the concentration of blowing agent) have a profound influence on the nucleation and growth rates of gas bubbles during mold filling. Some specific observations made from the present study are as follows: an increase in melt temperature, blowing agent concentration, and mold temperature brings about an increase in bubble growth but more non-uniform cell size and its distribution, whereas an increase in injection pressure (and hence injection speed) brings about a decrease in bubble growth but more uniform cell size and its distribution. Whereas almost all the theoretical studies published in the literature deal with the growth (or collapse) of a stationary single spherical gas bubble under isothermal conditions, in structural foam injection molding the shape of the bubble is not spherical because the fluid is in motion during mold filling. Moreover, a temperature gradient exists in the mold cavity and the cooling subsequent to mold filling influences bubble growth significantly. It is suggested that theoretical study be carried out on bubble growth in an imposed shear field under nonisothermal conditions.     

Characterization of molecular orientation in injection-molded thermoplastics by transmission and reflection infrared spectroscopy

Orientation in injection moldings of polypropylene (PP), polyethylene (PE), polyamide 6 (PA-6), and polystyrene (PS) was investigated by transmission and reflection infrared spectroscopy. Orientation of the surface was measured by the reflection method, the depth profiles of orientation and of the fraction of the crystalline phase were measured by the transmission spectroscopy of microtome sections. The maximum of orientation of PP lies in the subsurface layer (ca. 250 μm); the crystalline phase is oriented more than the amorphous one. The maximum of the depth profile of orientation corresponds to the minimum of the fraction of the crystalline phase in PP. The profile of orientation of PE Is similar; at the beginning (to a depth of about 500 μm) the parallel orientation of the c axis of the crystalline phase is the most distinct one, towards the center the orientation of the a axis passes from the perpendicular to the parallel one. Under the described molding conditions PA-6 is not significantly oriented, the fraction of the crystalline phase increases towards the center of the molding. Unoriented PA-6, the surface layer of which was removed by milling, has a highly oriented surface due to its mechanical treatment. No pronounced orientation of PS was observed under the molding conditions used.     

Synthesis,characterization, and mechanical properties of an injection moldable polyimide based on 1,4-diaminobutane

A partially aliphatic polyimide was synthesized in a two-step process in N-methylpyrrolidone (NMP) from 3,3′,4,4′-benzophenonetetracarboxylic dianhydride (BTDA) and 1,4-diaminobutane (DAB). Weight average molecular weights ranging from 35,000 to over 160,000 were obtained by adding different amounts of the chain stopper phthalic anhydride, or by using a slight excess of BTDA. Rheological measurements, supported by a size exclusion chromatography (SEC) analysis before and after injection molding, point to branching or even partial crosslinking during molding of poly(BTDA-DAB) if reactive amine endgroups are present. By reacting these amine endgroups with benzoyl chloride, branching is limited and a more Newtonian flow is observed. Both non-endcapped and endcapped reactor powders are ∼60% crystalline (Tg = 170 to 175°C, Tm = 290 to 300°C), but according to wide and small angle X-ray scattering (WAXS and SAXS) studies on test bars, both the more linear polyimides and their branched counterparts are fully amorphous after injection molding. Nevertheless, poly(BTDA-DAB) shows interesting mechanical properties like a bending modulus of ∼3.9 GPa, a tensile strength of ∼130 MPa, a tensile elongation at break of ∼13%, and a notched Izod impact of ∼4 kJ/m².     

A new approach for kinetic modeling and optimization of rubber molding

Although extensive research has been carried out on the understanding of the complex vulcanization process, the influence of reversion through exposure time and temperature on the vulcanization degree remains unclear. Therefore, the main aim of this study was a novel optimization approach that can help the industrial practitioners to select the optimal operating parameters, exposure time, and molding temperature, to achieve desired vulcanization degree of selected product. Spheres of four different diameters (2.5, 5, 10, and 20 cm) were selected as test geometry for simulation and optimization of rubber molding. Obtained vulcanization rheometer data for commercially available rubber blend (NR/SBR) were fitted by a new modeling approach, dividing vulcanization curve into two fitting sets: curing and reversion. The heat transfer equations for chosen geometry were coupled with proposed kinetic model. A new temperature-dependent kinetic parameter x, as the maximal reversion degree, was introduced, enabling determination of the lowest operating molding temperature (T_min = 132.36 °C), preventing high reversion and overheating of the rubber product. The final optimization goal was assessment of the optimal temperature and vulcanization time dependence on the rubber products dimensions. Proposed models have precise prediction with R² values greater than 0.8328 and MAPE less than 2.3099%.     

Experimental investigation of flow-induced microvoids during impregnation of unidirectional stitched fiberglass mat

The complexity of the resin injection step in liquid composite molding (LCM) processes, such as resin transfer molding (RTM) and structural reaction injection molding (SRIM), often results in flow-induced defects such as poor fiber wetting and void formation. These defects have a deleterious effect on the mechanical properties of composites. In this work, high resolution video-assisted microscopy was used for in situ observation of flow-induced interstitial voids or microvoids formed inside the fiber tows during mold filling. Flow visualization experiments were carried out with different liquids to better understand the microscale flow behavior that led to the formation of microvoids for flow both along and normal to the fiber tows. Microvoid formation was correlated to the modified capillary number, Ca#* = μν/γcos(θ). The study revealed that for axial flow, microvoids were formed at Ca#* > 10⁻³. For transverse flow, microvoids were formed at an even lower capillary number. ∼ 10⁻⁴. Once formed, microvoids were difficult to purge and remained trapped even after bleeding the liquid at much higher flow rates than those at which they were formed.     

Effects of interfacial morphology on the welding strength of injection‐molded polyamide

The effect of interfacial morphology controlled by injection‐molding conditions on the welding strength of injection‐molded polyamide was investigated in this article. The experimental results showed that the first injection‐molding conditions had distinct influence on the welding strength at the low secondary injection‐molding temperature T₂ (≤265°C), but the influence vanishes at T₂ ≥ 285°C. On the other hand, no matter what the first injection‐molding conditions are, the welding strength increases with increasing T₂, and when T₂ ≥ 285°C, the highest welding strength reaches 45 MPa, due to the formation of trans‐crystals at the interface. Morphology studies showed that trans‐crystals grow along the perpendicular direction of the interface, and their nuclei are formed at the surface of the first injection‐molded specimens. For the specimens with high‐welding strength, the welding strength relies on the skin layer of the first injection‐molded specimens in which the fracture induced by shear stress happens. POLYM. ENG. SCI., 47:2164–2171, 2007. © 2007 Society of Plastics Engineers     

Hydrodynamic molding method — a tool of resource-saving technology in ceramic and refractory production

A concept of ceramic refractory technology is formed, based on advanced examples of material nano-, micro-and macrotechnology, of the technique of high and elevated pressure (0.1–1.0 GPa), high-speed (pulsed, 5–15 msec) loading and molding of powder heterocompositions in hydrodynamic machines of the HDM class, performed under the action of propellant explosive substances (ES), manufactured from inexpensive artillery powders. Control of dynamic and production parameters for molding objects is provided by the weight of ES charge or the charging density in the hydrodynamic machine (HDM) combustion chamber. Scientific and technical bases created in GNU IPM NAN Belorussii for ceramic and refractory technology based on high energy pulsed compaction make it possible to organize and assimilate output of a broad range of objects for the ceramic and refractory industries. Translated from Novye Ogneupory, No. 7, pp. 48–49, July 2008.     

Study on modified phenolic resin. III. Modification with p-hydroxyphenylmaleimide/acrylic ester copolymer

The improvement of toughness and heat resistance of phenolic resin was examined by blend of novolac and copolymers prepared from p-hydroxyphenylmaleimide (HPMI) and acrylic ester. Copolymers of HPMI and acrylic esters, such as methyl acrylate, ethylacrylate, n-butylacrylate, or 2-ethylhexyl acrylate, were synthesized. Average molecular weights, glass transition temperatures (T_g) and thermal decomposition temperatures were measured. The miscibility of the copolymers with novolac was evaluated. It was found that these copolymers had higher average molecular weight and higher thermal decomposition temperature than those of novolac; they also had good miscibility with novolac. Molding compounds were prepared by hot roll-kneading of mixtures, which involved novolac, the copolymer, hexamethylenetetramine (hexamine), and glass fiber. Test pieces of the modified phenolic resins were prepared by transfer molding from the molding compounds. It was found that phenolic resin, modified with HPMI/ethylacrylate copolymer or HPMI/n-butylacrylate copolymer, which consisted of numerous units of acrylic ester, showed both good toughness and good heat resistance.     

Optical monitoring of polyesters injection molding

An optical fiber sensor similar to the one developed by Thomas and Bur 1 was constructed for the monitoring of the crystallization of three polyesters during the injection molding process. The polyesters studied were: polybutylene terephthalate (PBT), polytrimethylene terephthalate (PTT), and polyethylene terephthalate (PET). With this optical system it was possible to obtain, in real time, some essential parameters of the polyester crystallization kinetics at different processing conditions. Thus, a study of the influence of injection molding variables on the nonisothermal crystallization kinetics of these polyesters was done. The processing variables were: mold wall and injection temperatures, T_w and T_i, respectively; flow rate, Q; and holding pressure, P_h. The experiments were done following a first order central composite design statistical analysis. The morphology of the samples was analyzed by polarized light optical microscopy, PLOM. The signal of the laser beam during the filling and the crystallization stages of the injection molding of these materials was found to be reproducible. The measurements showed that this system was sensitive to variations of the crystallization of different types of polymers under different processing conditions. The system was not able, however, to monitor the crystallization process when the crystallinity degree developed by the sample was very low, as in the PET resin. It was also observed that T_w and T_i were the most influential variables on the crystallization kinetics of PBT and PTT. Due to its slower crystallization kinetics, PTT was found to be more sensitive to changes in these parameters than the PBT. © 2005 Wiley Periodicals, Inc. J Appl Polym Sci 99: 563–579, 2006     

Isocyanate trimerization kinetics and heat transfer in structural reaction injection molding

Guidelines are developed for molding large composite parts via structural reaction injection molding using glass preforms and polyisocyanurate resins. These are based on numerical simulations of the simultaneous heat transfer and reaction kinetics of a commercial system during and after mold filling. Premised requirements are that resin does not gel before the mold is filled, yet, reactions are sufficiently vigorous to approach completion. An existing mechanistic kinetic model is used and material parameters found from a chemical kinetics study employing an insulated cup. It is found desirable to use a high mold temperature and a low preform temperature in molding. Nondimensionalization of the governing equations reveals the existence of a Nusselt number (N_u), which describes the relative importance of heat transfer between resin and glass relative to thermal diffusion to the mold wall. With a Nusselt number of about 50 or higher it is possible to use the cooling capacity of the preform to extend gel time. The magnitude of N_u is influenced by part thickness, glass fraction, strand diameter, and flow velocity. Thus, the effect of the preform on extending resin gel time is within control of the molder.     

Multi-objective optimization of injection molding parameters,based on the Gkriging-NSGA-vague method

Plastic production quality, manufacturing cost, and molding efficiency are three important indices for a new product development. In addition to injection molding process parameters (IMPP), runner system also has an important role in the injection molding process. In this study, the plastic production quality, manufacturing costs, and molding efficiency are considered as the optimized objectives. The design parameters include runner diameters and IMPP. The improved Kriging surrogate model (Gkriging), nondominated sorting genetic algorithm (NSGA-II), and multicriteria fuzzy decision-making approach (vague sets) are combined, and the Gkriging-NSGA-vague scheme is proposed to optimize the runner diameters and the IMPP. Firstly, the Gkriging model is established to map the correlation between design parameters and optimized objectives. Based on the Gkriging model, the NSGA-II is combined with predictive models to obtain the Pareto-optimal solutions. Then, the optimal Pareto-optimal solution is obtained by the vague approach. A multicavity mold with two different plastic parts is utilized as the design case. The optimization results indicate that the Gkriging-NSGA-vague method is a powerful method for solving the multi-objective optimization problems. © 2019 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2019 , 137, 48659.     

Comparative study on the properties of wood polymer composites based on different modified soybean oils

The growing awareness for greener and more sustainable technologies has focused the attention of researchers recently for the development of high performance biopolymer-based composites. Wood polymer composites (WPC) based on functionalized epoxidized soybean oil (ESO) and soft wood, Krishnachura (Delonix regia), were prepared by compression molding technique. ESO was functionalized by acrylic acid (AESO), methacrylic acid (MESO), and methacrylic anhydride (MAESO), which were used as matrices in the composite. Wood flour from soft wood was used as reinforcing agent. The fiber/resin ratio was maintained at 40:60. The composites were characterized by Fourier transform infrared (FTIR) spectroscopy, nuclear magnetic resonance (NMR) spectroscopy, scanning electron microscopy (SEM), and thermogravimetric analysis (TGA). Mechanical testing, limiting oxygen index (LOI), and swelling behavior were checked for the prepared composites. WPC based on methacrylic anhydride exhibited maximum improvement in properties.     

Improving mold sets for large-size components prepared from aqueous slips. Part 3. Designs of mold sets

An integrated study has been made on searching for new mold set designs and technological solutions to eliminate the effect of nonuniform buildup of ceramic preforms on the rejection rate. New molding equipment is proposed equipped with a molding monitoring system and an innovative centering device, which makes it possible to decrease the rejection rate in molding. __________ Translated from Novye Ogneupory, No. 7, pp. 48–52, July, 2006.     

Application of citric acid as natural adhesive for wood

The development of natural adhesives derived from nonfossil resources is very important for the future. Besides, it is desirable to be safe adhesives without using harmful chemical substances. In this study, application of citric acid as a natural adhesive was investigated. Citric acid powder and bark powder obtained from Acacia mangium were used as raw materials. Citric acid powder was mixed with the bark powder, and the resulting powder mixture was poured into a metal mold. The mold was hot‐pressed at 180°C and 4 MPa for 10 min, and a bark molding was then obtained. The specific modulus of rupture and modulus of elasticity values of the molding containing 20 wt % citric acid were 18.1 MPa and 4.9 GPa, respectively. The molding did not decompose during a repeated boiling treatment. To clarify the effect of tannin on the adhesiveness of molding, bark was separated into tannin and residue. The molding was not obtained while using the tannin due to the marked fluidity, whereas it was obtained while using the residue, the same as while using the bark. It was considered that components other than tannin contributed to the adhesiveness. Based on the results of Fourier transform infrared spectra, the formation of ester linkages between carboxyl groups derived from citric acid and hydroxyl groups in the bark was confirmed. Accordingly, citric acid brought an adhesion by chemical bonding, and it could be used as a safe natural adhesive. © 2011 Wiley Periodicals, Inc. J Appl Polym Sci, 2012