PVC autoclave model

The batch reaction of polyvinyl chloride (PVC) in a pressure autoclave is modelled by considering the various mechanisms for conversion from vinyl chloride monomer (VCM) to the polymer during the middle phase of the industrial process. A key step is to determine at what stage the droplets of VCM stop contracting because of the density difference between VCM and PVC - this is known as the 'freeze point'. A model is proposed that locates the freeze point as that point where the unfavourable energy due to wetting of the PVC by water is dominated by the energy required to compress the gel network inside the droplets. Preliminary investigations support this explanation and suggest avenues for further work. A corollary of this model is an explanation of the role of 'secondary granulating agents' in controlling the porosity of the final product

Composite bulkhead fabrication development

Composite bulkhead is produced by a fabrication concept utilizing vacuum and/or autoclave pressure to hold preformed welded sandwich elements in place during bonding and aging

High molecular weight first generation PMR polyimides for 343 C applications

The effect of molecular weight on 343 C thermo-oxidative stability (TOS), mechanical properties, and processability, of the first generation PMR polyimides was studied. Graphite fiber reinforced PMR-15, PMR-30, PMR-50, and PMR-75 composites (corresponding to formulated molecular weights of 1500, 3000, 5000, and 7500, respectively) were fabricated using a simulated autoclave process. The data reveals that while alternate autoclave cure schedules are required for the high molecular weight resins, low void laminates can be fabricated which have significantly improved TOS over PMR-15, with only a small sacrifice in mechanical properties

Low-void polyimide resins for autoclave processing

Development of an advanced A-type polyimide, which can be used to produce autoclave molded, low-void content composites suitable for use at temperatures up to 316 C is reported. It consists of a mixture of methyl nadic anhydride, an 80:20 molar ratio of methylene dianaline and thiodianilene, and pyromellitic dianhydride

Development of autoclave moldable addition-type polyimides

Chemistry and processing modifications of the poly(Diels Alder) polyimide (PDA) resin were performed to obtain structural composites suitable for 589 K (600 F) service. This work demonstrated that the PDA resin formulation is suitable for service at 589 K (600 F) for up to 125 hours when used in combination with Hercules HTS graphite fiber. Sandwich panels were autoclave molded using PDA/HTS skins and polyimide/glass honeycomb core. Excellent adhesion between honeycomb core and the facing skins was demonstrated. Fabrication ease was demonstrated by autoclave molding three-quarter scale YF-12 wing panels

Effect of Autoclave Cycles on Surface Characteristics of S-File Evaluated by Scanning Electron Microscopy

Introduction: Presence of surface defects in endodontic instruments can lead to unwanted complications such as instrument fracture and incomplete preparation of the canal. The current study was conducted to evaluate the effect of autoclave cycles on surface characteristics of S-File by scanning electron microscopy (SEM). Methods and Materials: In this experimental study, 17 brand new S-Files (#30) were used. The surface characteristics of the files were examined in four steps (without autoclave, 1 autoclave cycle, 5 autoclave cycles and 10 autoclave cycles) by SEM under 200× and 1000× magnifications. Data were analyzed using the SPSS software and the paired sample t-test, independent sample t-test and multifactorial repeated measures ANOVA. The level of significance was set at 0.05. Results: New files had debris and pitting on their surfaces. When the autoclave cycles were increased, the mean of surface roughness also increased at both magnifications (P<0.05). Moreover, under 1000× magnification the multifactorial repeated measures ANOVA showed more surface roughness (P<0.001). Conclusion: Sterilization by autoclave increased the surface roughness of the files and this had was directly related to the number of autoclave cycles. Keywords: Autoclave; Endodontic Instruments; Root Canal Therapy; Scanning Electron Microscopy; Surface Characteristi

Development of autoclavable polyimides

A poly(Diels-Alder) (PDA) resin approach was investigated as a means to achieve autoclavability of high temperature resistant resin/fiber composites under mild fabrication procedures. Low void content Type A-S graphite reinforced composites were autoclave fabricated from a PDA resin/fiber prepared from an acetone:methanol:dioxane varnish. Autoclave conditions were 477K (400F) and 0.7 MN/sq m (100 psi) for up to two hours duration. After postcure at temperatures up to 589K (600F), the composites demonstrated high initial mechanical properties at temperatures up to 561K (550F). The results from isothermal aging studies in air for 1000 hours indicated potential for long-term ( 1000 hours) use at 533K (500F) and shorter-term (up to 1000 hours) at 561K (550F)

Ultrasound in gas–liquid systems: Effects on solubility and mass transfer

The effect of ultrasound on the pseudo-solubility of nitrogen in water and on gas–liquid mass transfer kinetics has been investigated in an autoclave reactor equipped with a gas induced impeller. In order to use organic liquids and to investigate the effect of pressure, gas–liquid mass transfer coefficient was calculated from the evolution of autoclave pressure during gas absorption to avoid any side-effects of ultrasound on the concentrations measurements. Ultrasound effect on the apparent solubility is very low (below 12%). Conversely ultrasound greatly improves gas–liquid mass transfer, especially below gas induction speed, this improvement being boosted by pressure. In typical conditions of organic synthesis: 323 K, 1100 rpm, 10 bar, kL a is multiplied by 11 with ultrasound (20 kHz/62.6 W). The impact of sonication is much higher on gassing out than on gassing in. In the same conditions, this enhancement is at least five times higher for degassing

Advanced modeling of the out-of-autoclave thermoplastics prepreg consolidation

Nowadays, composite materials are replacing metallic ones thanks to their excellent mechanical performances and reduced weight. However, many difficulties are encountered during composite forming processes. In fact, autoclave curing process is too expensive and limits the part size to the autoclave dimensions. Out-Of-Autoclave processes reduce substantially the cost of forming processes. However, the absence of autoclave pressure in out-of-autoclave manufacturing processes leads nowadays to high porosity and poor consolidation at the interface between the tows [1]. Moreover, the effect of the process parameters on the consolidation is still unknown and thus controlling the final parts quality is not obvious. Despite the high potential offered by the Out-of- Autoclave processes, only few researches has been made in the last few years, in order to quantify the consolidation of the tows while using such processes [2]. In fact, only few models addressing void dynamics in thermoplastic composites has been carried out [3, 4]. In this work, we are using a novel coupled approach involving modeling and simulation in order to quantify the consolidation in Out-of-Autoclave processes. Advanced model reduction techniques (POD, PGD ...) are employed in order to predict thermal fields during manufacturing processes and coupled to the subsequent squeeze flow