Filtern
Dokumenttyp
Schlagworte
- Elastomer (8)
- Compression set (6)
- DSC (5)
- Dichtungen (5)
- Dynamic mechanical analysis (5)
- Elastomere (5)
- Druckverformungsrest (4)
- Glass transition (4)
- Low temperature behaviour (4)
- Sealing material (4)
- Tieftemperaturverhalten (4)
- Ultrasound (4)
- Curemeter (3)
- DMA (3)
- Dichtung (3)
- EVA (3)
- Prepreg (3)
- Vulcanization (3)
- Cross-linking (2)
- Cure process (2)
- Glasübergang (2)
- Low temperature (2)
- Acoustic propagation (1)
- Autoclave (1)
- Bauteilversuche (1)
- CFC (1)
- Carbon fibre (1)
- Component test (1)
- Composites (1)
- Cross linked polyethylene insulation (1)
- Crosslinking (1)
- Crystal melting (1)
- Cure monitoring (1)
- Curing (1)
- Degree of cure (1)
- Degree of curing (1)
- Dielectric relaxation (1)
- Elastomers (1)
- Epoxy (1)
- Ethylene vinyl acetate (1)
- Ferroelectric polymer (1)
- Gelation (1)
- Injection moulding (1)
- Klebfolie (1)
- Leakage rate (1)
- Mechanical variables measurement (1)
- Natural rubber (1)
- O-Ring (1)
- O-Ringe (1)
- O-ring (1)
- On-line monitoring (1)
- Online control (1)
- P(VDF-HFP) (1)
- Photovoltaik (1)
- Poly(vinylidene(fluoride - hexafluoropropylene) (1)
- Rheology (1)
- Rubber seals (1)
- Seal (1)
- Silicone rubber (1)
- Sound velocity (1)
- TMDSC (1)
- Thermal analysis (1)
- Tiefe Temperatur (1)
- Ultrasonic (1)
- Uniaxial stretching (1)
- Vitrification (1)
- Vulcanisation (1)
EVA is a widely used material for the encapsulation of photovoltaic modules. It melts at elevated temperatures, and seals the module before it is crosslinked at temperatures above 130 °C by a peroxide-initiated crosslinking reaction. EVA has good optical properties necessary for application in solar modules. For process optimization and quality management, a method for the quick and reliable characterization of EVA crosslinking behaviour is of great value. Here, the practicability of ultrasound for online crosslinking monitoring is demonstrated. A sound velocity increase of about 8 m/s during the crosslinking reaction is found. The ultrasound results are compared with rheometer measurements performed with a curemeter typically used for the investigation of rubber crosslinking.
Epoxy carbon-fibre prepreg, Hexcel Type 6376 HTS, was investigated using Dynamic Mechanical Analysis (DMA). The DMA characteristic parameters are storage modulus E', loss modulus E' and loss factor tanδ. These parameters are ideally suited to observe the vitrification, referred to as glass transition, resulting from the cross-linking reaction. Detection of the cure state may also be achieved by determining the momentary glass transition temperature of partially cured samples. The consequent use of a multi-frequency measuring regime was used to derive the apparent activation energy for the glass transition process. Different temperature programs were also applied to monitor the curing process directly, as well as to investigate the different states of incomplete cure reached in preceding curing steps. The intention was to provide better understanding of the consequences of an interrupted autoclave curing process and to use DMA to detect the cure state achieved. With DMA, the continuation of an incomplete curing process also can be monitored. DMA measurements up to 300 °C showed, furthermore, that the final glass transition temperature was reduced by thermal degradation at high temperatures.
Carbon-fibre prepregs have found widespread use in lightweight applications. They are based on a carbon-fibre fabric impregnated with reactive epoxy resin. Prepreg materials are generally pre-cured so that they have a higher molecular weight than typical resins in order to reduce resin flow, which facilitates storage and later processing properties.
The measurements were carried out using commercially available materials and follow the published DMA investigations of the same material. TMDSC was used to find the correlation between curing conditions, the degree of cure and glass transition temperature. TMDSC has the advantage over standard DSC that it enables better determination of the glass transition temperature, which is often accompanied by an exothermic curing reaction, and thus overshadowed. The influence of the amplitude of temperature modulation was tested in preliminary experiments. For non-cured material a glass transition temperature of approximately 0 °C was determined; whereas for the totally cured material it was approximately 230 °C. The changes in degree of cure, temperature of actual glass transition and post-reaction are given as a function of curing time at 180 °C. The correlation between actual glass transition temperature and degree of cure is derived.
Carbon fibre prepregs have found widespread application in lightweight constructions. They are based on a carbon-fibre fabric impregnated with reactive epoxy resin. DMA measurements under temperature conditions similar to an autoclave programme were carried out using commercially available prepreg material with a high glass transition temperature. The characteristic of the temperature programme was a dynamic heating segment at 1.5 K/min followed by a longer isothermal segment at 180 °C. The courses of the storage modulus E', loss modulus E'' and tanδ were recorded. The measuring frequency was varied between 1 Hz and 33.3 Hz. Gelation and vitrification are assigned. The influence of the measuring frequency on the time to vitrification and the correlation with DSC are discussed. The reaction does not end even after 10 h curing at 180 °C, which is interpreted as the slow cessation of the reaction caused by vitrification.
Rubbers are widely used as main sealing materials for Containers for low and intermediate level radioactive waste and as additional component to metal seals in spent fuel and high active waste containers. The save enclosure of the radioactive container inventory has to be guaranteed according to legislation and appropriate guidelines for long term storage periods as well as down to temperatures of -40 °C for transportation. Therefore the understanding of failure mechanisms that lead to leakage at low temperatures is necessary to ensure a proper material choice which is certainly also influenced by additional factors as e.g. the aging behavior.