【正文】 substantially reduces the effective depth of penetration of ultraviolet light into the surface of an article formed from such a position.Mohamed et al. pointed out that barbituric acid and thiobarbituric acid are nontoxic organics, thermally stable materials of high melting point. Both contain active methylene groups, and can act as Hdonor 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 thioanalogue as thermal stabilizers for rigid PVC.The effective stabilization often requires a bination of antioxidant system in which plementary overlap of different mechanistic pathways involved. This act often referred to as synergism, is the motivation for the use of admixing position of dibutyltin 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 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 par