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1、外文资料翻译 A study on usability of magnesium oxide with titanium dioxide in PVC door and window profiles1. IntroductionPolyvinyl chloride is among the most widely used synthetic organic polymer materials. Plasticized polyvinyl chloride compositions are widely encountered as, for instance,vinyl sheet goo
2、ds and as objects formed from plastisols.Polyvinyl chloride is commercially available in a variety of grades, some of which are suitable for preparing rigid,plasticizer-free compositions for extrusion .For plastics, prolonged exposure to the suns electromagnetic radiation in the ultraviolet (UV) reg
3、ion can lead to photooxdiation and degradation of physical properties, often manifested by color change and embrittlement. Similarly,the UV component of ordinary fluorescent lighting can degrade polymers and many of the additives used with them.The effective UV radiation that does reach the earths s
4、urface extends from about 290400 nm. This range happens to include the highest energy component UV band, and the segment around 300 nm, which is the most distractive to plastics. Some man-made high-energy radiation sources mercury arc lamps, xenon arcs, carbon arcs, and various sun-lamps can emit ra
5、diation at wave lengths below 290 nm and these can degrade plastics even more severely than natural sun light. Hence, they are often used for accelerated testing of plastics.The energy content of UV radiation in the 290400 nm can rupture most of the chemical bonds present in polymer structures. Not
6、all the polymers are equally affected by UV radiation, and some have a degree of resistance, otably polymethyl methacrylates and fluorocarbons. Others, that in their pure forms could be expected to be resistant to UV, are degraded because of contaminants present that act as sites for UV energy absor
7、ption.Absorption of radiation energy by polymer produces molecular excitations: if the level of absorbed energy is high enough, it can activate a chemical reaction whereby internal bonds (carbon to carbon, carbon to hydrogen, carbon to halogen, etc.) are broken so that polymer degradation results. P
8、VC is damaged by dehydrochlorination (release of hydrogen chloride), autooxidation and echanochemical chain scission. This degradation is caused by the simultaneous sequence of these reactions.Dehydrochlorination, prevailing reaction during processing,leads to increasing discoloration. In the course
9、 of the proceeding degradation the physical properties are also changed in the direction of increasing embrittlement. PVC of ideal constitution should be thermally stable, which was concluded from investigations with model substances. Therefore, it has to be assumed that the damage, articularly the
10、dehydrochlorinations, starts from sites of the macromolecule with labile chlorinecarbon bonds. PVC can be degraded by heat and sun lights. The release of hydrogen chloride, which is the indication of PVC degradation in prolonged exposure to the suns electromagnetic radiation in the UV region, is occ
11、urred according to the following reactions:The color of PVC-based article is changed from yellow to black according to degrees of the degradation. Once the reaction has started, polymers quickly and progressively experience changes in appearance: surface qualities, gloss, chalking, color, electrical
12、 properties, tensile strength and elongation; and can reach the end points of embrittlement and total disintegration.The degradation of polymers exposed to UV, often described as photodegradation and frequently identified as photooxidation, can follow various routes. By absorbing UV radiation direct
13、ly, a polymer molecule can reach a high-energy excited state where it becomes unstable. If the excess energy can be dissipated in a fashion that does not affect the molecule by making it phosphoresce or fluoresce, or by converting the energy to heat that can be carried away, or by transferring the e
14、nergy to another molecule, photochemical reaction does not started and thus, polymer degradation will not happen. However, such actions occur only rarely, since most polymers cannot dispose of the excitation energy without undergoing a chemical reaction that sets off a degradative process.In theory,
15、 many pure polymers should not absorb UV radiation, and thus, not be subject to photodegradation. However, in practice the most polymers contain impurities such as carbonyl or carboxy groups or hydroperoxides that readily absorb radiation in the 290400 nm range causing them to break down. Thus, gene
16、rating sites within the polymer structure where chemical reactions can be initiated and propagated by free radicals. The active groups may be unavoidably present as a result of reactions that occur during polymerization. Similarly, metallic ions are present in most polymers as residues from polymeri
17、zation catalysts, or as constituents of compounding additives such as heat stabilizers, antioxidants, colorants, fillers and others. The metal ions are highly receptive to the absorption of UV radiation, and are efficient in transferring the absorbed energy to the polymer molecules around them, thus
18、, they act as photo-sensitizers and can promote degradation at the same time that they perform their desired functions.Another contributor to photodegradation of polymers is oxygen, which helps any free radicals that may be liberated by the UV to initiate and propagate oxidation of the polymer, henc
19、e, the term photooxidation.Polyvinyl chloride suffers from poor heat stability. Its degradation occurs by autocatalytic dehydrochlorination initiated at the labile sites in the polymer chains. This leads to severe discoloration and loss of mechanical properties. The dehydrochlorination most probably
20、 proceeds by a chain mechanism involving radical intermediates. Various defect sites in PVC are branching.Inorganic and organic thermal stabilizers are commonly added to protect the polymer from heat degradation. Among the most widely used ultraviolet stabilizers is titanium dioxide pigment. Filling
21、 a polyvinyl chloride composition with this pigment substantially reduces the effective depth of penetration of ultraviolet light into the surface of an article formed from such a composition.Mohamed et al. pointed out that barbituric acid and thiobarbituric acid are nontoxic organics, thermally sta
22、ble materials of high melting point. Both contain active methylene groups, and can act as H-donor through their enolic hydrogen groups, which can intervene with the radical species derived from the thermal degradation of PVC. They investigated the possibility of using barbituric acid and its thioana
23、logue as thermal stabilizers for rigid PVC.The effective stabilization often requires a combination of antioxidant system in which complementary overlap of different mechanistic pathways involved. This act often referred to as synergism, is the motivation for the use of admixing composition of dibut
24、yltin maleate and trinitro and its ester homologues. The stabilization agents of dibutyltin maleate and trinitro esters could retard somewhat the photodegradation of PVC. It is hoped that the total stabilizing effect of this admixed system should be greater than the sum of the individual effects whe
25、n PVC is subjected to an environment where the effects of heat and UV are combined. Turoti et al. investigated the effect of the stabilizing action of admixed mixtures of dibutyltin maleate and trinitro and its ester homologues on polyvinyl chloride exposed to natural atmosphere. In their study, the
26、 degradation and stabilization reactions were monitored by color formation, tensile strength and elongation at break, reduced viscosity as well as determination of time to embrittlement. It is observed that the stabilized PVC sample has an effective reduction in degradation reactions.Titanium dioxid
27、e is by far the most important of white inorganic pigments and possesses all-round suitability. While rutile titanium dioxide is highly reflective at visible wavelengths, it is also highly absorptive at ultraviolet wavelengths. However, although titanium dioxide is a highly effective ultraviolet lig
28、ht stabilizer for polyvinyl chloride compositions, it does have several serious drawbacks. An important disadvantage is the cost of titanium dioxide which has historically tended to be high compared with filler or extender pigments such as calcium carbonate and talc. Another significant disadvantage
29、 of using titanium dioxide as an ultraviolet stabilizer in unplasticized polyvinyl chloride compositions is that historically titanium dioxide has been periodically in short supply.The relatively high cost of titanium dioxide is an especially significant disadvantage for the manufacture of articles
30、for exterior use from unplasticized polyvinyl chloride compositions because such articles must often have substantially greater dimensions, for structural reasons than the effective penetration depth of ultraviolet light in the articles. Thus, it is highly desirable to able to reduce the level of ti
31、tanium dioxide in such a composition without experiencing an accompanying increase in the rate of degradation and reduction in service life. Although it seems to decrease the level of titanium dioxide in the PVC composition will tend to increase the effective penetration depth of ultraviolet length
32、and will consequently accelerate the degradation of the PVC, the experimental observations do not support such an expectation. Since PVC compositions consist generally of from about 0.55 parts by weight of rutile titanium dioxide per hundred parts by weight of the polyvinyl chloride, there is no gua
33、rantee for the bulk of titanium dioxide to locate near the external surfaces of articles exposed to sun lights.In this study, usability of magnesium oxide with titanium dioxide in the PVC compositions for forming of the exterior articles such as door and window profile is investigated in terms of de
34、termining discoloration and some mechanical properties of the articles under accelerated weathering test.2. Materials and methodsPVC compositions widely used to form the exterior articles such as door and window profiles consist essentially of about five parts (by weight) stabilizers, five parts rut
35、ile titanium dioxide, five parts fillers, and 0.1-3 parts process aids per hundred parts by weight of the polyvinyl chloride resin.Polyvinyl chloride is subject to thermal degradation by dehydrochlorination. Since many processes for forming useful objects from polyvinyl chloride compositions, such a
36、s extrusion and molding, subject the composition to elevate temperatures, most include thermal stabilizing agents that tend to inhibit thermal degradation of the polymer during processing. Example of commonly employed thermal stabilization agents includes barium/cadmium and organotins including merc
37、aptides, maleates and carboxylates.Polyvinyl chloride is also subject to degradation by exposure to ultraviolet light. Articles formed from polyvinyl chloride compositions, which are exposed to ultraviolet light such as vinyl siding and vinyl window and window frame components typically include an u
38、ltraviolet stabilizer.In this study, five different compositions of PVC were used to fabricate door and window profiles. These profiles are faded under accelerated weathering conditions. Discoloration and some mechanical properties of the profiles are determined to choose the most suitable polyvinyl
39、 chloride composition used to form the exterior articles.For window profiles up to nine repeated extrusion processes were investigated. The properties like impact strength, modulus, Vicat temperature, thermal stability, etc. of recycled window frame profiles from 20 to 25 years old windows are deter
40、mined, it is shown that such recycled PVC is suitable for reprocessing. The heat impact of PVC bottle materials during the recycling process at 160 180 was investigated by IR- and UV-spectroscopy and by DSC. The bottle samples are slightly and considerably affected at these temperatures as shown by
41、determination of the formed decomposition products, colour change, loss of volatile components and peroxide formation in air. However, since these decompositions occurred at about 30 min of experimental time which is about six-fold of that of real process times, the reclaimed material was found recy
42、clable which makes the use of this material in the production of window sections, profiles, pipes and even bottles possible. Investigations on the mechanical properties of recycled PVC bottle material separated from the postconsumer waste stream show significant reduction in strength and ductility.
43、It is believed that the main reason for this is the presence of impurities, especially PET, which although present at levels below 0.5% had a large effect on the properties. Also investigated was the degradation that occurs during multiple reprocessing of recycled PVC from post-consumer bottles usin
44、g IR-analysis and molecular weight measurements. Batches of recycled flake and powder as well as pure but processed bottle flake materials were subjected to simulated multiple recycling using a torque rheometer. The results indicated a rapid degradation of the recycled material compared with purer b
45、ottle flake PVC. Multiple recycling of bottle flake mixed with 0.2% polyethylene showed that the PE impurities accelerate the degradation process. Restabilization by adding new bottle flake material surprisingly prevented degradation even at small levels of new material (30%) and even after 15 recyc
46、ling steps. Recycled PVC bottle material can be used successfully in calciumzinc stabilized PVC foam formulations to produce profiles of saleable quality. Increasing amounts of bottle recyclate had no significant effect on gelation time, melt rheology or plate-out characteristic and gave rise to an
47、improvement on thermal stability. Foam blends can be extruded to produce profiles of good surface finish and low foam density. Up to 100% PVC bottle recyclate did not affect the density, cell structure or impact properties of co-extruded foam profiles. Foamed PVC recyclate can also be used for inner
48、 layers in tubes where densities at about 0.5 g/cm3 arepossible. The reuse of recycled PVC in cable insulations is described in Ref. For this purpose, it is necessary to recover copper and PVC from cable forms originating from used motor cars. PVC can be dissolved and separated to be reused in cable
49、 and wire insulating. It is reported that cables using 100% recycled PVC have successfully passed preliminary tests. Cable forms with 50% PVC recyclate have been released for the production of new cars by several manufacturers. Since 1990 PVC floor coverings were collected and recycled in Germany. First results and practical experiences are reported in Ref. Other recycling concepts have been developed for use of recycled PVC packaging or bottle material as core in co-extruded cellular profiles. The products had satisfact
