Local thermo‐oxidative degradation in injection molding

A loss in part properties and service life is caused by thermal, mechanical, and thermo‐oxidative stress during processing of thermoplastic materials. Process related thermal and mechanical stresses are inevitable. However, processing under exclusion of oxygen can reduce the thermo‐oxidative stress. A lower thermo‐oxidative stress can yield a higher transparency of optical parts, less reduction of average molecular weight for example in microinjection molding, and a longer service life due to less consumption of stabilizers during processing. For a cost‐effective and gentle process it is important to know at which step of processing the polymer is exposed to thermo‐oxidative degradation and where the oxygen comes from causing degradation. To study the local thermo‐oxidative stress, an injection molding machine was encapsulated and run under local exclusion of oxygen. As reported in this article, thermo‐oxidative degradation occurs in the plasticating unit due to oxygen from the surrounding air and oxygen dissolved in the polymer resin. POLYM. ENG. SCI., 2008. © 2008 Society of Plastics Engineers     

Technical/Economical Evaluation of Sugarcane Bagasse Hydrolysis for Bioethanol Production

In an attempt at improving bioethanol production, a bench‐scale comparison has been performed between the traditional one‐step process of sugarcane bagasse hydrolysis with 70 % sulfuric acid, and a modified operation including a second step with more dilute acid, at higher temperature. The influence of the reaction time, the percentage of solids in the sugarcane bagasse suspension and temperature on the hydrolysis efficiency, was investigated. Although the modified protocol allows for an appreciable improvement in the yield of conversion to fermentable sugars in comparison to the one‐step hydrolysis, a technical/economical analysis demonstrated that it would demand higher production costs and a longer payback period. Therefore, the latter process should be recommended for the setting up of a pilot plant with a production capacity of 80 m³ of alcohol per day.     

Penicillium commune spore production in solid‐state fermentation of coffee pulp at laboratory scale and in a helical ribbons rotating reactor

Penicillium commune was grown on coffee pulp (CP) by solid‐state fermentation (SSF). The effects of the duration of CP thermal treatment and the effects of incubation temperature on spore production yield were studied at laboratory scale. The effect of mixing during fermentation was assayed at pilot plant scale in a 70 L stainless steel non‐aseptic reactor equipped with helical ribbons for mixing solids. For thermal treatments of CP at 121 °C for 10, 20, 30 and 40 min, no significant difference in spore production yield was observed. Maximum sporulation yield was found at 25 °C; when the incubation temperature was higher than 30 °C, the sporulation yield decreased significantly. A spore production yield of 3.7 × 10⁹ spores g^?1 dry CP was obtained when continuous mixing (0.25 rpm) was used at pilot plant scale; however, a decrease in spore yield (1.4 × 10⁹ spores g^?1 dry CP) was observed under static conditions. Spore production was not affected when a scale factor between 79 and 105 was assayed from laboratory to pilot plant; at this level, the productivity obtained was 3.1 × 10⁷ spores g^?1 dry CP h^?1. This value is similar to that found in other reports using natural substrates but working at a smaller scale. Copyright © 2006 Society of Chemical Industry     

Particle‐scale modeling of coal devolatilization behaviors for coal pyrolysis in thermal plasma reactors

A generalized heat transfer and devolatilization model coupled with the thermal balance between the heating gas and particles was established to predict the complex coal pyrolysis behaviors in the practical plasma reactors. It was proved that this model could well describe the coal devolatilization behaviors in both the pilot‐scale and lab‐scale plasma reactors as the mechanisms of coal chemistry and particle‐scale physics were incorporated. The achieved understanding on the reactor energy balance demonstrated that the heat recovery of the quenching process was crucial to the thermal efficiency and economic benefit of the overall project. The in‐depth discussion of the influences of coal feed rate and particle size on the reactor performance revealed the dominant roles and presented the optimal values of these two factors. In particular, the simulation results of several coals could help to provide a simple, quick method of coal type selection for industrial plasma processes. © 2014 American Institute of Chemical Engineers AIChE J, 61: 913–921, 2015     

New bleeding model of additives in a polypropylene film under atmospheric pressure II

Many additives are commercially used to add more favorable qualities to films. The bleeding process by which the additive in a film comes to the surface is considered. A new bleeding model of additives in a polypropylene film under atmospheric pressure was investigated. Solubility and diffusion are found to be important for explaining this bleeding process. It was found that the experimental results were explained more precisely by assuming a two‐step transport process between the crystalline regions and the amorphous ones. The solubilities and diffusion coefficients of UV‐stabilizers such as 2‐(2H‐benzotriazol‐2‐yl)‐4‐(1,1,3,3‐tetramethylbutyl)phenol and 2‐(2H‐benzotriazol‐2‐yl)‐4‐methylphenol were determined at 40°C. The difference between the saturation solubilities and the diffusion coefficients of UV‐stabilizers was discussed by comparing with the results of molecular dynamics (MD) simulation. © 2007 Wiley Periodicals, Inc. J Appl Polym Sci 2007     

Structure and thermal degradation of poly(N‐phenyl acrylamide) and poly(N‐phenyl methacrylamide)

Poly(N‐phenyl acrylamide) (PPA) and poly(N‐phenyl methacrylamide) (PPMA) were prepared by using N‐phenyl acrylamide and N‐phenyl methacrylamide as monomer, respectively, in tetrahydrofuran using azobisisobutyronitrile as initiator. FT‐IR, ¹H‐NMR, and GPC were used to characterize their molecular structure. The PPA obtained exhibited higher molecular weight and wider molecular weight distribution than that of PPMA. Their thermal degradation and kinetics were systematically investigated in two atmospheres of nitrogen and air from room temperature to 800°C by thermogravimetric analysis at 10°C/min. Based on the thermal decomposition reactions in nitrogen and air, it is shown that a three‐step degradation process in nitrogen and a four‐step degradation process for two polymers were observed in this investigation. The initial thermal degradation temperature was lower than 190°C. Under two atmospheres, PPA exhibits higher degradation temperature, higher temperature at the maximum weight‐loss rate, faster maximum weight‐loss rates, and larger weight loss for the first‐stage decomposition, as well as higher char yield at 500°C than those of PPMA. © 2003 Wiley Periodicals, Inc. J Appl Polym Sci 88: 1065–1071, 2003     

Modelling decomposition and fire behaviour of small samples of a glass‐fibre‐reinforced polyester/balsa‐cored sandwich material

This publication presents the experimental and numerical methods to model the devolatilization process of a glass‐fibre‐reinforced polyester/balsa‐cored sandwich material on small scale. The fundamental modelling of the source term in pyrolysis‐based fire simulations requires as input data the thermochemical properties of solid fuel and the kinetic parameters of the devolatilization process. First, the thermal decomposition of both elements composing the sandwich structure was studied by thermogravimetry coupled with gas analysis, in air and pure nitrogen atmospheres at several heating rates, in order to define a comprehensive multi‐step reaction pathway. A differential equation system is defined to model these decomposition processes. The kinetic parameters were then estimated by solving the system of equations by an inverse problem. Second, the fire behaviour of each element was studied separately and then combined in the sandwich structure on the cone calorimeter. In addition, numerical simulations with Fire Dynamics Simulator were performed to gradually assess the ability of the model(s) to reproduce each element composing the sandwich structure. Numerical and experimental results are compared and then discussed. Overall, the model provides a good agreement with the experimental data and encourages to model higher scales. Copyright © 2012 John Wiley & Sons, Ltd.     

Cross‐Scale Modeling and Simulation of Coal Pyrolysis to Acetylene in Hydrogen Plasma Reactors

Coal pyrolysis to acetylene in hydrogen plasma is carried out under ultrahigh temperature and milliseconds residence time. To better understand the complex gas‐particle reaction behavior, a comprehensive computational fluid dynamics with discrete phase model has been established, with special consideration of the particle‐scale physics such as the heat conduction inside particle. The improved chemical percolation devolatilization model that incorporates the tar cracking reactions is adopted. The model predictions are in good agreement with the performances of two pilot‐plant reactors. The simulations reveal the detailed unmeasurable information of gas phase and particle‐scale behaviors, then point out the facts that coal devolatilization almost finishes in the first 100 mm of the reaction chamber and the optimal particle diameter is suggested to be 20–50 μm. The different reactor performances during the scale‐up from 2‐ to 5‐MW unit are analyzed based on the detailed simulation results in combination with the operational experience. © 2012 American Institute of Chemical Engineers AIChE J, 59: 2119–2133, 2013     

High‐resolution thermogravimetry of poly(phenylene sulfide) film under four atmospheres

The thermal degradation of poly(phenylene sulfide) (PPS) film is investigated in air, nitrogen, helium, and argon with different physical and reactive characteristics at room temperature to 790°C as ascertained by high‐resolution thermogravimetry (TG) at a variable heating rate in response to the changes in the sample's weight‐loss rate. Only a one‐step degradation process of the PPS is observed in nitrogen and argon, but a two‐step degradation process of PPS is found in helium. A four‐step degradation process of the PPS, which is hardly ever revealed by traditional TG, is found in this investigation, especially in air. The initial thermal degradation temperature and temperature at the first maximum weight‐loss rate of the PPS increase in the following order: helium < nitrogen < argon < air. The first maximum weight‐loss rate also increases with the variation of the atmosphere in the order nitrogen < air < argon < helium. The char yield at 700°C increases in the order air < helium < nitrogen < argon. The activation energy of the major degradation process of PPS, as calculated based on the high‐resolution TG data, is very high and increases in the order nitrogen < argon < helium < air. The thermal decomposition parameters of the PPS determined by the high‐resolution TG are systematically compared with those by traditional TG at a constant heating rate. © 2002 Wiley Periodicals, Inc. J Appl Polym Sci 83: 1940–1946, 2002     

Continuous computer controlled production of formate dehydrogenase (FDH) and isolation on a pilot scale

A continuous production process has been developed up to pilot scale (300 l) for FDH production with the methylotrophic yeast Candida boidinii. A high cell mass specific FDH activity (50 U/g) is achieved by process computer controlled supply of pure methanol to operate the reactor at an optimum methanol concentration of 10 g/l. The maximum FDH spacetime yield achievable with this process control involves a residence time of 7 h. The FDH space-time yield (STY) and FDH concentration are a function of the oxygen transfer rate (OTR) of the fermenter (maximum STY = 255 U/(l h) at k_La = 870 l/h). For a reasonable compromise between high FDH space-time yield and high FDH concentration, an optimum residence time is adjustable by regulating the supply of nutrient salt solution in relation to the OTR of the fermenter. On a pilot scale (200 l continuously stirred tank reactor) roughly 4 million U of FDH were produced within 10 days at a residence time of 14.3 h. Isolation of intracellular FDH enzyme was performed using extraction with an aqueous two-phase system (PEG/K₂HPO₄). A technical product quality of 1.2 U/mg FDH was achieved without any chromatographic purification step.     

High‐resolution thermogravimetry of polyphenylene sulfide film under four atmospheres

Thermal degradation of polyphenylene sulfide (PPS) film was investigated in air, nitrogen, helium, and argon with different physical and reactive characteristics from room temperature to 790°C by a high‐resolution thermogravimetry (TG) at a variable heating rate in response to the changes in the sample's weight‐loss rate. In nitrogen and argon, only a single‐step degradation process of the PPS was observed, but in helium, a two‐step degradation process of PPS was found. Notably, in air a four‐step degradation process of the PPS, which was hardly ever revealed by a traditional TG, was found in this investigation. The initial thermal degradation temperature T_d and temperature at the first maximum weight‐loss rate T_dm1 of the PPS increased in the following order: in helium < in nitrogen < in argon < in air. The first maximum weight‐loss rate also increased with the variation of atmosphere in the order: nitrogen < air < argon < helium. The char yield at 700°C increased in the order: in air < in helium < in nitrogen < in argon. The activation energy of the major degradation process of PPS calculated based on the high‐resolution TG data was very high, increasing in the order: in nitrogen < in argon < in helium < in air. The thermal decomposition parameters of the PPS determined by the high‐resolution TG were systematically compared with those by traditional TG at a constant heating rate. © 2002 Wiley Periodicals, Inc. J Appl Polym Sci 83: 2053–2059, 2002     

Study on the macrokinetics of poly(trimethylene terephthalate) polycondensation reaction

The macrokinetics of poly(trimethylene terephthalate) (PTT) polycondensation reaction during the high‐vacuum process was studied. The results showed that PTT polycondensation reaction may be considered as a second‐order reaction and thermal degradation is negligible in mathematical handling. The intrinsic viscosity versus time undergoes two different processes according to temperature. The apparent reaction rate constants and apparent activation energy of PTT polycondensation reaction are smaller than those of PET. Under efficient stirring, PTT polycondensation reaction is still reaction‐controlled and the role of devolatilization could be neglected even during the high‐vacuum process. © 2004 Wiley Periodicals, Inc. J Appl Polym Sci 92: 1765–1770, 2004     

Thermo‐oxidative degradation behavior of recycled polypropylene

This study has been carried out to mimic the thermo‐oxidative degradation of polypropylene (co‐PP) during service life and recycling. Injection molded specimens were heat aged at 130°C for different times up to maximum of 300 h to simulate the degradation of co‐PP during the service life. These aged specimens were mixed with stabilizers in internal mixer and again heat aged up to 300 h. A small increase in melt flow rate (MFR) value was observed for aged co‐PP but it showed large increase after recycling. The presence of carbonyl peak at 1713 cm⁻¹ confirmed the oxidation of co‐PP during aging and it increases with aging time. Carbonyl index (CI) is increased in recycled sample with aging, whereas oxidation induction time (OIT) decreased. The stabilizers used during reprocessing are quite effective in controlling the thermo‐oxidative degradation of the polymer during processing and aging. The thermogravimetric analysis shows that the onset of degradation temperature starts at low temperature for recycled sample as compared to virgin co‐PP. © 2010 Wiley Periodicals, Inc. J Appl Polym Sci, 2011     

New advances in the mathematical modeling of the continuous bulk process for the production of high‐impact polystyrene using multifunctional initiators

New advances in the mathematical modeling of the bulk continuous high‐impact polystyrene (HIPS) process are presented. The model consists of three modules that allow the simulation of: (1) a polymerization reactor train, (2) a devolatilization (DV) stage, and (3) structure–properties relationships. The model is based on a kinetic mechanism that includes thermal initiation, chemical initiation by sequential decomposition of a multifunctional initiator, propagation, transfer to monomer, transfer to rubber, termination by combination and re‐initiation, as well as high temperature crosslinking and oligomer generation reactions. The present model is comprehensive from a kinetic perspective, since it can be used to simulate a HIPS process using initiators of any functionality and structure. The model is adjusted and validated using previously unpublished experimental data for bulk continuous HIPS polymerization in a pilot‐scale plant. The experimental work includes a series of polymerizations using three different multifunctional initiators: (1) luperox‐331 M80 (L331), (2) pinacolone diperoxide, and (3) diethyl ketone triperoxide. The pilot plant comprised the main stages of an industrial HIPS process: prepolymerization, finishing and DV. Theoretical results show a good agreement with the experimental measurements. POLYM. ENG. SCI., 59:E231–E246, 2019. © 2018 Society of Plastics Engineers     

乙丙橡胶湿法脱挥工艺研究

采用乙丙橡胶(J-2070)胶液进行了凝聚、挤出脱挥的实验研究。采用改造后的喷嘴结构及合理的加料方式,有效地提高了胶液凝聚过程中的脱挥效率。采用改造后的Ⅱ型模头,进行乙丙橡胶水凝聚样品的挤出脱挥实验,实验结果表明:在挤出机模头压力3.6 MPa机头温度为154℃时,挤出样品的w(总挥发分)0.5%;在挤出机转速为50~120 r/min的范围内,挤出样品不发生降解,说明该脱挥工艺可行,满足乙丙橡胶脱挥的要求。     

High‐resolution thermogravimetry of polyethersulfone chips in four atmospheres

Thermal degradation and kinetics of polyethersulfone (PES) chips were studied in air, nitrogen, helium, and argon from room temperature to 790°C by high‐resolution thermogravimetry (TG) at a variable heating rate in response to changes in the sample's degradation rate. In the four atmospheres, a two‐step degradation process in air, argon, and helium or a three‐step degradation process in nitrogen of the PES were found in this investigation. In particular, the three‐step degradation process in nitrogen of the PES revealed by the high‐resolution TG was hardly ever observed by a traditional TG. The initial thermal degradation temperature of the PES increases with the testing atmosphere in the following order: air < argon < helium < nitrogen but the activation energy of the first major degradation of PES increases in a different order: argon < nitrogen < helium < air. The degradation temperature, the temperature at the maximum weight‐loss rate, the maximum weight‐loss rate [(dα/dT)_m1 and (dα/dT)_m2], char yield at 790°C, and activation energy of the first major degradation process obtained by the high‐resolution TG were compared with those by traditional TG. The PES exhibits the largest (dα/dT)_m1 and the greatest char yield at 790°C in helium but the largest (dα/dT)_m2 and smallest char yield in air. A significant dependency of the thermal decomposition of the polymers on the physicochemical properties (density, thermal conductivity, and oxidative ability) of the testing atmospheres is elaborated for the first time. © 2003 Wiley Periodicals, Inc. J Appl Polym Sci 90: 3631–3637, 2003     

Characterization of the devolatilization rate of solid fuels in fluidized beds by time‐resolved pressure measurements

The characterization of volatile matter (VM) release from solid fuel particles during fluidized‐bed combustion/gasification is relevant to the assessment of the reactor performance, as devolatilization rate affects in‐bed axial fuel segregation and VM distribution across the reactor. An experimental technique for the characterization of the devolatilization rate of solid fuels in fluidized beds is proposed. It is based on the analysis of the time series of pressure measured in a bench‐scale fluidized‐bed reactor as VM is released from a batch of fuel particles. A remarkable feature of the technique is the possibility to follow fast devolatilization with excellent time‐resolution. A mathematical model of the experiment has been developed to determine the time‐resolved devolatilization rate, the devolatilization time and the volume‐based mean molecular weight of the emitted volatile compounds. Devolatilization kinetics has been characterized for different solid fuels over a broad range of particle sizes. © 2011 American Institute of Chemical Engineers AIChE J, 2012     

Generalized model of heat transfer and volatiles evolution inside particles for coal devolatilization

Devolatilization is acknowledged as the first important step in coal conversion techniques. A comprehensive heat transfer and devolatilization model was established, with special consideration of the particle‐scale physics and chemistry, to predict the internal heat transport and pyrolysis behavior of particles. The chemical percolation devolatilization model with corrected kinetic parameters and structure parameters was validated with a lot of experimental data and then adopted to describe the devolatilization behaviors under a broader range of temperatures, heating rates, and coal types. The newly achieved understanding of the integrated effect of heating rate and coal type on coal devolatilization could help to provide a preliminary coal rank selection method for industrial processes. In particular, in‐depth discussion of the influences of heat conduction, volatiles diffusion, and endothermic heat of devolatilization inside particle indicated the dominant roles of these factors when the intensity of heat transfer was strong or the release of volatiles was rapid. © 2014 American Institute of Chemical Engineers AIChE J, 60: 2893–2906, 2014     

Stabilization of poly(vinyl chloride) against photo‐degradation using dienophilic compounds

As dienophilic compounds, N‐ aminophenylmaleimides would be expected to act as radical traps and thus, could be investigated as organic photo‐stabilizers for rigid poly(vinyl chloride) (PVC). Their stabilizing efficiencies were evaluated by measuring the extent of discoloration and the change in the mechanical properties of the photo‐irradiated polymer. Their stabilizing efficiencies were compared with phenyl salicylate, which is a commonly used industrial photo stabilizer. The results have proved the higher stabilizing efficiency of all the investigated materials as compared with phenyl salicylate. The stabilizing efficiency of the aminomaleimides is attributed to their radical trapping potency which intervenes with the radical degradation of the photo‐irradiated PVC. Moreover, it was found that these materials lower the extent of discoloration of the polymer during later stages of degradation. This improvement in the color stability is most probably attributable to the ability of the aminomalemides to react by a Diels–Alder reaction with the conjugated double bonds created on the polymeric chains as a result of the degradation of the polymer. Finally, the results illustrate the blending of aminomaleimide derivatives with phenyl salicylate improve the photo stabilization of the polymer as shown from the absorbance coefficient Δa values, and this improvement attains its maximum when both the investigated stabilizers and phenyl salicylate are taken in equivalent ratios. The observed synergism is attributed to the combination of the mechanisms by which both stabilizers function. © 2009 Wiley Periodicals, Inc. J Appl Polym Sci, 2009     

Effect of Feedstocks on High‐Severity Fluid Catalytic Cracking

A novel fluid catalytic cracking (FCC) process, that utilizes a downer reactor, has been developed to enhance the yield of light olefins under high‐severity reaction conditions. The effect of heavier feedstock on this high‐severity fluid catalytic cracking (HS‐FCC) process has been investigated using a small‐scale HS‐FCC pilot plant (0.1 b/d). Hydrotreated and virgin vacuum gas oils (VGO), hydrotreated and virgin atmospheric residues (AR) were used as test‐feeds in a previous study. The yield of desired products, such as gasoline and light olefins, produced from virgin VGO cracking was 79 wt.‐%, which is much higher than that obtained from a conventional FCC process. In the case of hydrotreated VGO, the yield of desired products decreased to 76%, however. On the other hand, AR feeds exhibited a performance similar to VGO with a slight increase in coke formation. In this study microactivity test (MAT) results are reported in which the activity and selectivity of the Y‐zeolite based catalyst is evaluated. Kinetic modeling was also done based on a four‐lump reaction model.