【正文】 ped that the total stabilizing effect of this admixed system should be greater than the sum of the individual effects when PVC is subjected to an environment where the effects of heat and UV are bined. 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 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 dioxide is by far the most important of white inorganic pigments and possesses allround 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 light stabilizer for polyvinyl chloride positions, it does have several serious drawbacks. An important disadvantage is the cost of titanium dioxide which has historically tended to be high pared with filler or extender pigments such as calcium carbonate and talc. Another significant disadvantage of using titanium dioxide as an ultraviolet stabilizer in unplasticized polyvinyl chloride positions 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 for exterior use from unplasticized polyvinyl chloride positions 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 titanium dioxide in such a position without experiencing an acpanying increase in the rate of degradation and reduction in service life. Although it seems to decrease the level of titanium dioxide in the PVC position will tend to increase the effective penetration depth of ultraviolet length and will consequently accelerate the degradation of the PVC, the experimental observations do not support such an expectation. Since PVC positions consist generally of from about –5 parts by weight of rutile titanium dioxide per hundred parts by weight of the polyvinyl chloride, there is no guarantee 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 positions for forming of the exterior articles such as door and window profile is investigated in terms of determining discoloration and some mechanical properties of the articles under accelerated weathering test.2. Materials and methodsPVC positions widely used to form the exterior articles such as door and window profiles consist essentially of about five parts (by weight) stabilizers, five parts rutile titanium dioxide, five parts fillers, and 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 positions, such as extrusion and molding, subject the position to elevate temperatures, most include thermal stabilizing agents that tend to inhibit thermal degradation of the polymer during processing. Example of monly employed thermal stabilization agents includes barium/cadmium and organotins including mercaptides, maleates and carboxylates.Polyvinyl chloride is also subject to degradation by exposure to ultraviolet light. Articles formed from polyvinyl chloride positions, which are exposed to ultraviolet light such as vinyl siding and vinyl window and window frame ponents typically include an ultraviolet stabilizer.In this study, five different positions of PVC were used to fabricate door and window profiles. These profiles are faded under accelerated we