Identification of rheological and structural characteristics of foamable poly(ethylene terephthalate) by reactive extrusion

The reactivity and efficiency of five low molecular weight multifunctional anhydride and epoxy compounds as chemical modifiers of a bottle grade poly(ethylene terephthalate) (PET) resin were evaluated by reactive extrusion under controlled conditions. The two dianhydrides and the three epoxy compounds were used at concentrations based on stoichiometry derived from the measured carboxyl and hydroxyl end group contents of the base resin. Measures of melt viscosity, melt strength, intrinsic viscosity and carboxyl group content were used as criteria of the extent of the modification. Correlations of die pressure with extrudate swell during extrusion, and melt flow index (MFI) with melt strength by off‐line testing of the extrudates permitted the ranking of the modifiers according to their chain‐extending/branching efficiency. For some systems molecular weight increases (related to die pressure/MFI/intrinsic viscosity) accompanied by broadening of the molecular weight distribution (related to die swell/melt strength) were considered excessive. Extrusion foaming experiments with one particular dianhydride modifier that increased the intrinsic viscosity of the resin from 0.71 to 0.9 dl g^?1 indicate that production of low‐density foams by a process involving one‐step reactive modification/gas injection foaming is feasible, at conditions not significantly different from those employed in the simple reactive modification of the PET resin. The rheological and structural parameters determined in this work may be used as criteria to specify PET foamable compositions in terms of types and concentrations of modifiers. Copyright © 2004 Society of Chemical Industry     

回收PET瓶片/接枝PE反应共混物的形态及性能

利用有反应活性的各种接枝聚乙烯(PE)作为回收聚对苯二甲酸乙二酯(PET)瓶片的改性剂,使接枝PE上的活性酐基与PET的端羟基在不同的挤出设备中熔融反应,制备相分散均匀、力学性能较好的PET基工程塑料.结果表明,挤出设备的选择对混合效果影响较大,缩聚型反应挤出机和双螺杆挤出机比普通单螺杆挤出机具有更优良的混合效果;各种接枝PE的改性效果优劣次序是:马来酸酐接枝线型低密度聚乙烯,马来酸酐接枝低密度聚乙烯,马来酸酐接枝高密度聚乙烯;接枝PE添加质量分数为20%时,可大幅度提高反应共混物的冲击性能.     

Microwave heating controlled reactive melt infiltration for graphite-Si-SiC ceramics manufacturing

In this work, we investigated a procedure which exploits microwave ovens to produce SiC- based components by reactive melt infiltration of silicon into graphite preforms. The employed oven is designed to grant optical access to the sample surface, which allows to measure its temperature evolution though a noncontact pyrometer. This signal was used as a feedback to control the power provided to the preform and as an experimental output whose analysis provides insight into the reaction mechanism. Specifically, it is found that complete infiltration is achieved much before the end of the reaction. The latter is not fully self-sustained as the global reaction rate continuously decreases with time until it is no more able to keep the temperature above the silicon solidification value. At that point, the reaction stops. The analysis of the processed samples proved that this procedure allows producing fully infiltrated samples without material failure by adjusting the heat provided during the infiltration stage rather than by tuning the preform structure and composition, which is the usual approach. The proposed method is less time and energy consuming than the standard one.     

Monitoring the evolution of PET branching through chemorheology

There is a high interest in modifying the rheological properties of polyethylene terephthalate (PET) through structural modifications while maintaining its thermoplastic nature. This article reports real‐time spectroscopic and rheological monitoring of the effects of reactive melt modification of PET with a multi‐functional epoxide—triglycidyl isocyanurate (TGIC)—that lead to chain extension/branching and subsequently formation of gel‐like structures. An infrared spectroscopic technique to monitor the simultaneously occurring degradation and chain extension/branching reactions was evaluated. The effects of reaction temperature, shear rate, and residence time were also investigated. Frequency scans at various time intervals on the reacting samples provided information on changes in the degree of branching and melt elasticity. The effect of method of sample preparation for chemorheological testing was also evaluated in this study. A 50% excess of the stoichiometric amount of TGIC for complete reaction with terminal carboxyl groups resulted in a self‐similar polymeric structure of PET near the sol‐gel transition point or a critical gel formation whose linear viscoelastic properties obey scaling law. An estimated fractal dimension from the experimental results was used to quantify the evolution of the branched network structure during the reactive melt modification. Polym. Eng. Sci. 44:474–486, 2004. © 2004 Society of Plastics Engineers.     

通过反应挤出提高聚丙烯的熔体强度

利用反应挤出技术研究了不同反应物对聚丙烯(PP)熔体强度的影响。考察了不同用量的低密度聚乙烯(LDPE)、乙烯-乙酸乙烯酯共聚物(EVA)、季戊四醇三丙烯酸酯(PETA)、二乙烯基苯(DVB)以及上述物质的混合物在过氧化二异丙苯的引发下对PP熔体强度、熔体流动速率、熔垂的影响。结果表明,LDPE、EVA的加入对产物熔体强度的影响有限,PFTA也只能使其提高1倍左右;而DVB的加入可使产物的熔体强度显著提高,仅加入1％就可使熔体强度提高20倍,熔垂实验也证明了这一点;几种反应物混合使用效果不如单独使用好。     

反应型纳米碳酸钙补强NR的研究

采用具有反应性的改性剂,在纳米碳酸钙水悬浮液中进行改性,制备一种新型改性纳米碳酸钙（简称M-CaCO3）及其与NR的复合材料,对改性前后纳米碳酸钙的结构和形态进行分析,并对NR/纳米碳酸钙复合材料的结构和性能进行研究.结果表明,与未改性纳米碳酸钙相比,改性纳米碳酸钙的透过率下降,在正己烷中的分散性明显提高;NR/M-CaCO3复合材料具有良好的界面相容性和耐热分解性能、较高的交联密度以及优良的综合物理性能和耐老化性能,M-CaCO3的最佳用量为8份.     

利用反应挤出的聚丙烯熔融接枝改性

系统简介了聚丙烯熔融接枝体系的组成、机理及实现熔融接枝的反应挤出技术。介绍了聚丙烯接枝物的表征和应用状况，并指出了熔融接枝体系中存在的问题。     

Influence of polyfunctional monomer on melt strength and rheology of long‐chain branched polypropylene by reactive extrusion

Long chain branching (LCB) were added to linear polypropylene (PP) using reactive extrusion in the presence of selected polyfunctional monomers (PFMs) and a peroxide of dibenzoyl peroxide (BPO). Fourier Transformed Infrared spectra (FTIR) directly confirmed the grafting reaction occurred during the reactive extrusion process. Various rheological plots including viscosity curve, storage modulus, Cole‐Cole plot, and Van‐Gurp plots, confirmed that the LCB structure were introduced into modified PPs skeleton after modification. In comparison with linear PP, the branched samples exhibited higher melt strength, lower melt flow index, and the enhancement of crystallization temperature. The LCB level in modified PPs and their melt strength were affected by the type of PFM used and could be controlled by the PFM properties and structure. PFMs with lower boiling points, such as 1, 4‐butanediol diacrylate (BDDA), could not produce LCB structure in modified PP skeleton. The shorter molecular chain bifunctional monomers, such as 1,6‐hexanediol diacrylate (HDDA), favored the branching reaction if their boiling points were above the highest extrusion temperature. And some polar groups, such as hydroxyl, in the molecule of PFM were harmful to the branching reaction, which might be attributed to the harm of the polarity of groups to the dispersion of PFM in PP matrix. © 2010 Wiley Periodicals, Inc. J Appl Polym Sci, 2010     

A temperature‐dependent adaptive controller. Part II: Design and implementation

A generic online temperature‐dependent adaptive control procedure to redefine the controller parameters was developed from dynamic models to achieve good tracking of injection‐velocity setpoint profiles during filling of a mold cavity. This adaptive control procedure (ACP) incorporates algorithms for process open‐loop testing and modeling, control simulations, and online controller updating. These functionalities are embedded into a main program that provides overall control of mold‐filling velocity. The controller's dynamic matrix is updated as changes in the setpoint melt temperature occur. It was shown that the ACP can provide an effective and systematic approach for controlling injection mold‐filling velocity for any plastic material over its operating melt temperature range. Polym. Eng. Sci. 44:1934–1940, 2004. © 2004 Society of Plastics Engineers.     

Moldability studies in reactive polymer processing

Reactive polymer processing is the combined polymerization and processing of reactive prepolymers in a single operation. It encompasses a wide variety of processing methods including Reaction Injection Molding (RIM), a relatively new and growing fabrication method. Reaction Injection Molding utilizes impingement mixing of low viscosity fluids, injection of the reactive mixture into a mold, and polymerization therein to enable the molding of large plastic items. Polyurethane is currently the most commercially utilized RIM material although a number of other systems such as epoxy, nylon, and polyester are also suitable. Non-urethane systems such as epoxy are often not as amenable to the process, however, since they are slower reactions and have a potentially damaging exotherm. A comprehensive analysis was developed to determine if a molding system is processable by RIM. Criteria for processability were established and include the ability to mix on impingement, fill large molds characteristic of the process, and provide a short cycle time without promoting a damaging exotherm. The treatment, consisting of both experimental and numerical techniques, was applied to identify potential epoxy molding systems, establish their processing window, and conduct an optimization of the process parameters to evaluate productivity. The analysis and its conclusions are applicable to most reactive polymer processing operations that employ a rapid, exothermic, polymerization reaction.     

Surface properties of polyamides modified with reactive polydimethylsiloxane oligomers and copolymers

Surface modification of polyamide-6 (PA-6) was investigated by melt blending with silicone-urea copolymers or organofunctionally terminated polydimethylsiloxane oligomers. Blends were prepared in a laboratory scale high-shear melt mixer. Surface characteristics of the blends were determined by static water contact angle measurements and X-ray photoelectron spectroscopy. Effect of the type, composition, average molecular weight and amount of the silicone additive in the blends, on the surface properties were determined. Influence of the thermal history of the samples on the surface properties was also investigated. All of the blends showed formation of silicone rich surfaces. Surface modification was permanent due to either the formation of chemical bonds between additive and polyamide and/or very strong hydrogen bonding between urea and amide groups.     

Modification of rheological properties of a thermotropic liquid crystalline polymer by melt-state reactive processing

Thermotropic main-chain liquid crystalline polymers typically have very low melt viscosity with strong temperature dependence compared to other common thermoplastics. While this is beneficial in some processing applications, such as injection molding, it presents challenges for others, such as coextrusion. In this study, the rheological properties of a thermotropic main-chain liquid crystalline polymer (Vectra A950) were enhanced by melt-state reactive processing with triphenyl phosphite (TPP), which can react with up to three polymer chain-ends through their chain-end functionalities. The influence of processing time and TPP content on the shear viscosity and other important material properties were investigated. Optimal conditions, which increased the shear viscosity by nearly a factor of 20 over the neat polymer, were found to be 4 wt% TPP and 30 min of reaction time at 290 °C. Further results from differential scanning calorimetry, wide-angle X-ray diffraction and polarized optical microscopy confirmed that coupling with TPP did not affect the microstructure, melting/crystallization behavior or liquid crystallinity. The stability of TPP-modified samples was also studied at 80 °C in air and following melt reprocessing at 290–300 °C under N₂ or air. Samples were stable (as measured by shear viscosity) for more than one month at 80 °C in air or when reprocessed in N₂ at 290 °C for up to 10 min. However, when reprocessed at 300 °C in air, the viscosity enhancement was partially reversed due to scission of P–O bonds that were formed during the initial reaction between the polymer chain-ends and TPP.     

Parameters affecting the chain extension and branching of PET in the melt state by polyepoxides

This article describes the chemical modification of polyethylene terephthalate (PET) with a variety of compounds containing reactive glycidyl group(s). Four different modifiers, namely, diglycidyl ether of bisphenol‐A (DGEBA), N,N′‐bis[3(carbo‐2′,3′‐epoxypropoxy) phenyl] pyromellitimide (BGPM), triglycidyl glycerol (TGG), and triglycidyl isocyanurate (TGIC) were compared for their reactivity toward PET in the melt phase. It was found that the presence of tertiary nitrogen in the structure of the epoxide modifiers plays the role of in‐built catalyst for their reaction with the end groups of PET. TGIC as a modifier was selected for the detailed investigation of the simultaneously occurring degradation and chain extension/branching reactions in a batch‐melt mixer. The reactions were followed by torque changes, analyzing the products for residual carboxyl content, and by determining insoluble content. It is shown that the rate of the reactive modification of PET melt by TGIC depends upon stoichiometry, temperature, rate of shear, and the chemical composition and the molecular weight (MW) of the PET resin. In general, the results indicate an increase in melt viscosity and insoluble content, whereas an overall decrease in carboxyl content occurs, as defined by the choice of mixing conditions and stoichiometry. Analysis of the batch kinetic data can be useful to define the process requirements for carrying out the reactive modification in continuous extrusion equipment. © 2002 Wiley Periodicals, Inc. J Appl Polym Sci 87: 643–652, 2003     

Chemical finishing of cotton using reactive cyclodextrin

Chemical modification of cotton cellulose in the fabric form was investigated through reaction with monochloro-β-cyclodextrin. The reaction involves single ended substitution and crosslinking. Investigations into the factors affecting these reactions occurring in the presence of N-methylol compound (resin) and/or a reactive dye were undertaken. The treatment was carried out as per the conventional pad–thermofixation method.     

Modification of cellulose acetate with oligomeric polycaprolactone by reactive processing: Efficiency,compatibility, and properties

Oligomeric polycaprolactone (oPCL) was used for the modification of cellulose acetate by reactive processing in an internal mixer at 180°C, 50 rpm, 60 min reaction time, and 45 wt % caprolactone (CL) content. The product of the reaction was characterized by several analytical techniques and its mechanical properties were determined by dynamic mechanical thermal analysis and tensile testing. The synthesized oPCL contained small and large molecular weight components. The small molecular weight fraction plasticized cellulose acetate externally and helped fusion. Although composition and structure did not differ considerably from each other when CL monomer or polycaprolactone oligomer was used for modification, the grafting of a few long chains had considerable effect on some properties of the product. The large molecular weight chains attached to CA increased the viscosity of the melt considerably and resulted in larger deformability. oPCL homopolymer is not miscible with cellulose acetate and migrates to the surface of the polymer. Exuded polycaprolactone oligomers crystallize on the surface but can be removed very easily. More intense conditions may favor the grafting of long chains leading to polymers with advantageous properties. © 2009 Wiley Periodicals, Inc. J Appl Polym Sci, 2009     

Preparation of the anhydride terminated polycarbonate and its reactive compatibilization with polystyrene

Polycarbonate with anhydride end groups (PC‐anh) was prepared by the reaction between polycarbonate having hydroxyl end groups (PC‐OH) and trimellitic anhydride chloride (TMAC). Hydroxyl or anhydride terminated polycarbonates were characterized by Fourier transform infrared spectroscopy (FTIR) and nuclear magnetic resonance (NMR) spectroscopy. The reaction of PC‐anh with polystyrene containing oxazoline reactive groups (RPS) was confirmed not only by the torque measurement during melt blending of these two but also by FTIR spectroscopy of the reactive blend obtained. Polycarbonate (PC) / polystyrene (PS) compatibilized blends were prepared by melt blending along with their reactive counterparts, PC‐anh and RPS in the Haake mixer. The morphologies of these blends were examined by the scanning electron microscope (SEM). The compatibilized blends with reactive components showed relatively finer morphologies than the uncompatibilized blend without reactive components. Izod impact strength and rheological property of these blends were also investigated. © 2000 John Wiley & Sons, Inc. J Appl Polym Sci 77: 1338–1347, 2000     

Technological evaluation of reactive cyclodextrin in cotton printing with reactive and natural dyes

The chemical modification of cotton fabric with reactive cyclodextrin (R‐CD) at different concentrations was carried out to enhance the printability of cotton fabric. The extent of the modification reaction was expressed as %N. Reactive and natural dyes were used to print cotton fabric before and after modification. Printing pastes were applied immediately after preparation or after 24 h of storage. Printing fixation was performed through either steaming or thermal treatment. The effect of the incorporation of R‐CD in the printing paste of unmodified cotton was also studied. The results reveal that the extent of the modification reaction increased with increasing R‐CD concentration and so did the color strength (K/S) of the printed sample regardless of the dye used. The results also revealed that K/S of the R‐CD modified cottons were higher than that of the corresponding unmodified samples regardless of the method of fixation or the time elapsed before printing. On the other hand, the incorporation of R‐CD in the printing pastes of reactive dyes, namely, Cibacron Brown 6R‐P or Remazol Brilliant Red GG, had adverse effects, most probability due to the (a) increasing viscosity of the paste and/or (b) interaction of the reactive dye with R‐CD hydroxyls. The opposite held true when a natural dye was used. Further, the incorporation of R‐CD in the printing pastes had no effect on the rheological type of the pastes or the on overall fastness properties of the prints. Nevertheless, such an incorporation of R‐CD was accompanied by a remarkable increase in the magnitude of the apparent viscosity. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 102: 338–347, 2006     

Research on a New Variotherm Injection Molding Technology and its Application on the Molding of a Large LCD Panel

The polymer injection products produced by using the current injection molding method usually have many defects, such as short shot, jetting, sink mark, flow mark, weld mark, and floating fibers. These defects have to be eliminated by using post-processing processes such as spraying and coating, which will cause environment pollution and waste in time, materials, energy and labor. These problems can be solved effectively by using a new injection method, named as variotherm injection molding or rapid heat cycle molding (RHCM). In this paper, a new type of dynamic mold temperature control system using steam as heating medium and cooling water as coolant was developed for variotherm injection molding. The injection mold is heated to a temperature higher than the glass transition temperature of the resin, and keeps this temperature in the polymer melt filling stage. To evaluate the efficiency of steam heating and coolant cooling, the mold surface temperature response during the heating stage and the polymer melt temperature response during the cooling stage were investigated by numerical thermal analysis. During heating, the mold surface temperature can be raised up rapidly with an average heating speed of 5.4°C/s and finally reaches an equilibrium temperature after an effective heating time of 40 s. It takes about 34.5 s to cool down the shaped polymer melt to the ejection temperature for demolding. The effect of main parameters such as mold structure, material of mold insert on heating/cooling efficiency and surface temperature uniformity were also discussed based on simulation results. Finally, a variotherm injection production line for 46-inch LCD panel was constructed. The test production results demonstrate that the mold temperature control system developed in this study can dynamically and efficiently control mold surface temperature without increasing molding cycle time. With this new variotherm injection molding technology, the defects on LCD panel surface occurring in conventional injection molding process, such as short shot, jetting, sink mark, flow mark, weld mark, and floating fibers were eliminated effectively. The surface gloss of the panel was improved and the secondary operations, such as sanding and coating, are not needed anymore.     

Fracture toughness assessment of poly(ethylene terephthalate) blends with glycidyl methacrylate modified polyolefin elastomer using essential work of fracture method

The static fracture toughness of poly(ethylene terephthalate) (PET) melt blended with a modifier containing glycidyl methacrylate (GMA)‐grafted ethylene‐propylene rubber and homopolymerized GMA was studied on injection molded specimens by adopting the essential work of fracture (EWF) method. It was found that the essential and nonessential or plastic work both decrease with an increasing amount of modifier (up to 20 wt %) if the PET matrix is amorphous and nonaged. The scatter in the EWF data for the blend with 10 wt % modifier was found by presuming concurrent mechanisms between microcrystallization and morphology‐dependent cavitation and fibrillation processes. © 2000 John Wiley & Sons, Inc. J Appl Polym Sci 79: 842–852, 2001     

Chain extension of PA1010 by reactive extrusion by diepoxide 711 and diepoxide TDE85 as chain extenders

The chain extension behaviors of two diepoxides, epoxide TDE85 and 711, were studied to evaluate their coupling effects on polyamide 1010 (PA1010). The former gave better coupling effects and a faster reaction rate. The torque of PA1010 melt increased dramatically with reaction time. The effect of the diepoxy chain extender on the flowability, thermal properties, and mechanical properties of chain‐extended PA1010 was investigated. The melt flow index (MFI) dramatically decreased as the diepoxide was added to PA1010, and the notched Izod impact strength of the chain‐extended products also increased. Furthermore, study on the usage of chain extender showed that there exists an approximate platform on the curve of melt torque versus content of chain extender, beyond which crosslinking may occur. Theoretical analysis of the occurrence of crosslinking was carried out by Flory criterion, which demonstrated that the average amount of functional groups in the chain extension system played a significant role in avoiding crosslinking. © 2004 Wiley Periodicals, Inc. J Appl Polym Sci 94: 2347–2355, 2004