Polymeren: van keten tot kunststof / A. K. van der Vegt, L. E. Govaert. Author. Van der Vegt, A. K.. Other Authors. Govaert, L. E.. Published. Delft: VSSD, pdf converter. Quote. Postby Just» Tue Aug 28, am. Looking for polymeren van keten tot kunststof pdf converter. Will be grateful for any help! Top . Polymeren van keten tot kunststof / Catalog Record - Electronic Resource Kunnende dit werk verstrekken tot een vervolg van het werk van den Heer J. Hess Also issued electronically via World Wide Web; PDF reader required for full text.
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Wikify tag. HTML table needs to be converted to wiki markup. I'm no good at tables aracer.mobi pdf Deformation temperature at 10 kN needle load, source: A.K. vam der Vegt & L.E. Govaert, Polymeren,van keten tot kunststof, ISBN This will . Cached. Download as a PDF 2, Polymeren, van keten tot kunststof - Vegt, Govaert - (Show Context). Citation Context aracer.mobin,sZ. aracer.mobi,sY.  AK van der Vegt, LE Govaert, Polymeren van keten tot kunststof, vijfde druk, Bohn VSSD, Contact. 1,*: Avans Hogeschool, ATGM, Lectoraat “Biobased .
Such copolymers are advantageous for certain molding applications, such as thermoforming, which is used to make tray or blister packages from PET sheet sometimes called APET, for "amorphous PET". On the other hand, crystallization is important in other applications where mechanical and dimensional stability are important, such as seat belts. For PET bottles, the use of small amounts of CHDM or other comonomers can be useful: if only small amounts of comonomers are used, crystallization is slowed but not prevented entirely.
As a result, bottles are obtainable via stretch blow molding "SBM" , which are both clear and crystalline enough to be an adequate barrier to aromas and even gasses, such as the carbon dioxide in carbonated beverages. Crystallization occurs when polymer chains fold up on themselves in a repeating, symmetrical pattern.
Long polymer chains tend to become entangled on themselves, which prevents full crystallization in all but the most carefully controlled circumstances. PET in its natural state is a crystalline resin. Clear products can be produced by rapidly cooling molten polymer to form an amorphous solid. Like glass, amorphous PET forms when its molecules are not given enough time to arrange themselves in an orderly fashion as the melt is cooled.
At room temperature the molecules are frozen in place, but if enough heat energy is put back into them, they begin to move again, allowing crystals to nucleate and grow. This procedure is known as solid-state crystallization. Like most materials, PET tends to produce many small crystallites when crystallized from an amorphous solid, rather than forming one large single crystal.
Light tends to scatter as it crosses the boundaries between crystallites and the amorphous regions between them. This scattering means that crystalline PET is opaque and white in most cases. Fiber drawing is among the few industrial processes that produces a nearly single- crystal product.
PET is subject to various types of degradations during processing. The main degradations that can occur are hydrolitic, thermal and probably most important thermal oxidation.
When PET degrades, several things happen: discoloration, chain scissions resulting in reduced molecular weight, formation of acetaldehyde and cross-links "gel" or "fish-eye" formation.
Discoloration is due to the formation of various cromophoric systems following prolonged thermal treatment at elevated temperatures. This becomes a problem when the optical requirements of the polymer are very high eg in packaging applications. Acetaldehyde is normally a colorless gas with a fruity smell. It forms naturally in fruit, but it can cause an off-taste in bottled water. Acetaldehyde forms in PET through the "abuse" of the material. When acetaldehyde is produced, some of it remains dissolved in the walls of a container and then diffuses into the product stored inside, altering the taste and aroma.
This is not such a problem for non- consumables such as shampoo, for fruit juices, which already contain acetaldehyde or for strong-tasting drinks, such as soft drinks. For bottled water, low acetaldehyde content is quite important, because if nothing masks the aroma, even extremely low concentrations ppb of acetaldehyde can produce an off-taste. The thermal and thermooxidative degradation results in poor procesability characteristics and performance of the material.
One way to alleviate this is to use a copolymer. Comonomers such as CHDM or isophthalic acid lower the melting temperature and reduces the degree of crystallinity of PET especially important when the material is used for bottle manufacturing. This helps to prevent degradation, reducing the acetaldehyde content of the finished product to an acceptable that is, unnoticeable level.
See copolymers, above. Other ways to improve the stability of the polymer is by using stabilizers, mainly antioxidants such as phosphites. Recently, molecular level stabilization of the material using nanostructured chemicals has also been considered.
It remains in the material and can thus in principle migrate out into food and drinks. As antimony is very toxic, this is of concern. The Swiss Federal Office of Public Health investigated the amount of antimony migration, comparing waters bottled in PET and glass: the antimony concentrations of the water in PET bottles was higher, but still well below the allowed maximal concentrations.
A later study by a group of geochemists at the University of Heidelberg headed by William Shotyk  finds similar concentrations of antimony in Canadian water bottled in PET and, comparing it with concentrations in groundwater and in natural water bottled both in polypropylene and glass, concludes that much more Sb is comparatively leaching from PET.
Although EVLA has fewer side effects than conventional saphenous femoral ligation and stripping1e5 resulting in fewer haematomas, less postoperative pain, Materials and Methods paraesthaesia and time off work, the technique still can be improved.
Complications of EVLA include postoperative Materials and techniques ecchymosis, pain, bruising and periphlebitis. These are due to vein wall perforation and energy dissemination in the Our investigation was approved by the ethics committee for perivenous tissue6,7 and probably arise when the laser fibre animal experiments at the Catholic University of Leuven, tip frequently contacts the vessel wall during treatment.
Goat saphenous veins were used since the lateral This has been observed on ultrasound imaging. The goats were treated under general anaesthesia. When energy is delivered, direct contact between the Under ultrasound control Terason t laptop ultra- fibre tip and the vessel wall may result in ulceration or sound, Teratech, Burlington, USA access was obtained by perforation of the vein.
Physiological saline at into the surrounding tissue. We injected, on average, within the vein lumen, complications of EVLA may be ml of liquid around the target veins, equivalent to minimised. Ten veins were treated using a normal bare A new catheter fixed to the fibre was designed Fig. The shape of the self-expandable tip allows with- Spain , using a continuous pullback protocol. Power was set drawal from the fibre and catheter using the conventional to 8 W and pullback speed was adjusted to deliver a linear EVLA procedure.
This new catheter design was evaluated in endovenous energy density LEED 17 between 60 and an animal model. Figure 1 Tulip-shaped self-expandable catheter fixed to the fibre. Please cite this article in press as: Vuylsteke M, et al. The mean length of the treated segment was Six veins were removed immediately, eight Description of the fibre-tip catheter: tulip catheter veins after 10 days and six veins after 3 weeks.
Excised veins were prepared for histological examination. About The fibre-tip centring catheter Tobrix, Waalre, the 11e15 sections of each of these veins were taken at Netherlands consists of a hollow tube, fixed to the laser random.
This tube has tulip-shaped, self-expandable blades at The pathologists measured the diameter and the depth its distal end around the fibre tip. The tube is folded into of ulceration in the vein wall using a range of magnifica- an outer guiding catheter, which permits easy access to the tions. Each optical field correlates with a constant defined vein undergoing treatment.
When the outer guiding cath- diameter.
Eyepiece graticules were used for measurement eter is withdrawn pullback , the tulip-shaped blades at of the specimens. The perivenous tissue destruction was the distal end of this tube expand and push the vein wall Figure 3 Perivenous tissue destruction scale: the perivenous destruction is measured at three points A,B,C.
The distance between the edge of the outer vein wall and the surrounding fascia is divided into three parts 1,2,3. With this manoeuvre the fibre tip is centred intra- Table 1 Histological data of veins immediately removed luminally and prevents direct contact with the vein wall after treatment.
Group 1: without catheter.
Group 2: with Fig. This catheter is referred to below as the tulip catheter. Perivenous tissue destruction scale Fig. At three different points at the These destruction was measured. The extent of necrosis was graded following Table 1. In three of them, the new tulip catheter was used the scale: 0 Z no necrosis, 1 Z necrosis.
Consequently, at group 2. In both the groups, 39 sections were taken for each location, if the three layers were involved, the extent histological analysis.
Each part where necrosis is seen In the veins treated without the tulip catheter group 1 , was scored 1. Consequently, if the necrosis was seen in all an uneven destruction of the vein wall was seen, with three positions, the maximum necrosis can reach a score ulceration and perforation. Very limited perivenous equal to 9.
Perivenous tissue destruction was measured tissue destruction was seen at the point of perforation. Veins treated using the tulip catheter group 2 did not show any ulceration or perforation. The vein wall Measurements of perivenous temperature looked normal. Only a limited amount of carbonisation was found intraluminally. The intraluminal blood was dena- The temperature in the perivenous fluid used to simulate tured probably due to boiling.
No perivenous tissue tumescent anaesthesia was measured using thermocou- destruction was seen.
The extent of ulceration and ples thermocouple type K, Pronto tc, Thermo-Electric, perforation was significantly different between the two Balen, Belgium. One needle was inserted at the proximal groups. The Veins harvested 10 days after treatment n Z 8 Table location of the needle in the perivenous liquid in the 2 showed, in both the groups, a cell-rich necro-inflam- immediate proximity of the vein wall was checked by matory process surrounding the treated vein.
This newly perioperative ultrasound. The thermocouples were con- nected to a digital thermometer Pronto tc, Thermo- Electric, Balen, Belgium. Temperature was measured during fibre withdrawal to determine the maximum temperature for both the groups with and without tulip catheter. An a-level of significance of 0. Results Ten goats were treated according to the protocol described above.
The mean diameter of the veins was 0. LEED was and carbonisation at the point of direct contact. Group 2: with tulip-catheter. Group 2: with The destruction of the vein wall was far more extensive tulip-catheter.
The use of the tulip catheter almost completely elimi- nated ulceration and perforation after EVLA. Transmural destruction of the vein wall, with complete necrosis of the muscle cells, is expressed as a percentage of the total circumference of the vein wall. The mean peri- venous destruction score was of 3. Three weeks postoperatively Table 3 , six veins were harvested.
Organisation in and around the vein walls was very extensive. The inflammatory tissue was infiltrating the treated veins. Newly formed small vessels around the treated veins were accompanied by macrophages and histiocytes, removing the destroyed tissue and forming scar tissue.
At the points of perforation in the vein wall, there was deeper destruction of the perivenous tissue Fig. At these points, we found more carbonisation, which in some cases was encapsulated by polynuclear leucocytes.
This perivenous tissue destruction in some cases was clearly in regression due to the healing process.
The intraluminal content was mostly damaged with eosinophilic denaturation of the intravascular material. Major parts of the vein wall were destroyed and the muscle cells were necrotic, but sometimes in an uneven distribution.
Some parts were not destroyed or incompletely destroyed; the remaining vein wall encap- sulated the destroyed part by forming a new endothelial layer on the opposite side, forming a new lumen which Figure 5 Veins harvested 10 days after treatment.
The exact border of treated without catheter showing an ulcer with perivenous the ulceration was often difficult to establish.
More tissue destruction especially at the point of direct contact complete circumferential destruction was observed in the ulcer. There was no significant total circumference arrow. In eter showing a more circumferential vein wall destruction. Discussion EVLA of the incompetent saphenous vein is safe and is at least as effective as surgery. The tulip catheter minimised ulceration and perforation of the vein wall.
Veins removed immediately after treat- ment showed no perforation and only infrequent ulcera- tion when the tulip catheter was used.
The vein wall appeared to be untouched. We believe that prevention of vein wall perforation will lead to less postoperative ecchymosis. Veins removed 10 days after treatment showed greater circumferential vein wall destruction compared with the group in which the bare fibre was used. This proves that the direct contact between the fibre and the vein wall is not the most significant mode of action of EVLA.
In fact, direct contact is responsible for the ulceration and perforation due to the convection of heat energy from the fibre tip into the surrounding tissue7,13 and should be avoided if possible. Energy leakage through the perforations is responsible for perivenous tissue destruction and inflammation.
However, the temperature rise in the perivenous fluid did not differ significantly in the two groups, but there was a wide range of measurement.
This is probably due to the position of the thermocouple.