Dark time yellowing of white rigid vinyl outdoor weatherable compounds

Morris, Raymond A.; Prejean, Thomas G.; Green, John Glass

doi:10.1002/vnl.730080212

Cited by 5 publications

(1 citation statement)

References 16 publications

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“…An experimenter should check to see if the system under examination poses a significant problem in reversal, for this can influence the answer to the question of how much darkening or bleaching is the result of a given amount of exposure to heat or light (Morris et al 1985).…”

Section: Reversible Color Changesmentioning

confidence: 99%

Accelerated Aging, Photochemical and Thermal Aspects

Witte¹,

Feller²

1996

Studies in Conservation

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The Getty Conservation Institute, an operating program of the J. Paul Getty Trust, is committed to raising public awareness of the importance of preserving cultural heritage worldwide and to furthering scientific knowledge and professional practice in the field of conservation. The Institute conducts research, training, documentation, and conservation activities in several major areas including objects and collections, archaeological sites and monuments, and historic buildings and sites. Research in Conservation This reference series is intended to make available the findings of research conducted by the Getty Conservation Institute and its individual and institutional research partners, as well as state-of-the-art reviews of conservation literature. Each volume covers a separate topic of current interest and concern to conservators.

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Section: Reversible Color Changesmentioning

confidence: 99%

Accelerated Aging, Photochemical and Thermal Aspects

Witte¹,

Feller²

1996

Studies in Conservation

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Gelbfäurbung von weißpigmentiertem PVC bei Dunkellagerung nach Bewitterung

Hepp

1989

Angew. Makromol. Chem.

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ZUSAMMENFASSUNG:Bei der kunstlichen und natiirlichen Bewitterung von weiBen Fensterprofilmustern beobachtet man haufig eine Vergilbung, die mefltechnisch verfolgt werden kann durch Erfassung des b-Wertes. Diese Vergilbung entsteht wahrend der Dunkellagerungsphase und wird mit der Lange der Dunkellagerung verstarkt, bis sie eine gewisse Sattigung erreicht. Bei erneuter Exposition im Freien oder im Bewitterungsgerat ist diese Vergilbung reversibel. Es liegt die Vermutung nahe, dal3 es sich um ein Gleichgewicht zwischen Vergilbung im Dunkeln und Ausbleichen im Hellen handelt. Hierzu wurde ein Mechanismus vorgeschlagen, der den Zerfall von unter Sonneneinstrahlung gebildeten zyklischen Peroxiden im Dunkeln beinhaltet.Als Konsequenz dieser Arbeit sollte bei der Beurteilung von weil3em PVC-Material fur den AuBeneinsatz immer sofort nach Ende einer Expositionszeit die Farbveranderung gemessen werden, um Fehlmessungen, die durch langeres Lagern entstehen konnen, zu vermeiden und wirtschaftlichen Schaden von dem Produzenten abzuwenden. SUMMARY:When white window profile samples are artificially and naturally weathered, a yellowing is often observed that can be followed by measuring the b-value. This yellowing occurs during the dark storage phase and becomes increasingly pronounced the longer the duration of dark storage until it reaches a certain saturation point. With renewed exposure in the outdoor or in the weathering instrument this yellowing is reversible. This suggests that there is an equilibrium between yellowing in the dark and bleaching in the light. A mechanism was proposed for this that entails decomposition in the dark of cyclic peroxides formed by exposure to sunlight.As a result of this work, when assessing white PVC materials for outdoor use the color change should always be measured immediately at the end of the period of exposure. This will avoid measuring errors that can result from longer storage times and avert commercial losses from the manufacturer.

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Impact modifiers for PVC

Lutz¹

1993

J. Vinyl Addit. Technol.

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With the exception of most PVC pressure pipe and a few profile applications where high modulus is the major consideration, most rigid and semirigid PVC compounds have impact performance requirements that can be met only through the use of impact modifiers. We present an overview of the mechanisms of impact modification and the effects of impact modifier type and concentration, interaction with other formulation ingredients, and PVC morphology as they are influenced by processing conditions. Typical end use formulations are given to illustrate the selection and use of impact modifiers for various applications. HISTORY OF IMPACT MODIFICATIONarly attempts to extend the utility of PVC were E directed to softening or plasticization, both to enhance processability and to produce tougher (and flexible) articles (1). As the search continued for nonmigrating plasticizers and as the need for more rigid compounds became evident, internal modification or grafting/copolymerization of PVC with other monomers and polymers gained momentum (2). The major rubber companies (which also became the major PVC producers) began to develop and supply various modified PVC compounds that were intended for use "as-supplied" (3).In the early 1960s, powder-blending became more feasible and economically attractive to the end-user fabricators. The ability to inventory large quantities of PVC and a relatively small number of additives that could be used to tailor-make a wide variety of compounds improved the economics as well as performance and utility of rigid PVC compounds and products. The success of powder blending was largely due to the development of polymeric processing aids and impact modifiers.The "evolution" of materials useful as impact modifiers might be expressed chronologically as elastomers (41, elastomer/PVC grafts (5), ABS terpolymers (6), core-shell multipolymers (7). and "superfine" inorganic fillers. MODES AND MECHANISMS OF IMPACT MODIFICATIONUnlike "glassy" polymers that have sharp melt transitions, PVC goes through a virtual metamorphe sis involving the breakdown of its particulate structure (8). At each stage of the breakdown, PVC has different physical characteristics (9). Faulkner ( 10) and Summers, et al. (1 11, have shown that complete fusion of PVC is necessary to give the ultimate in toughness, primarily as reflected in optimum tensile strength. Other investigators suggest that unmodified rigid PVC compounds develop optimum toughness (as measured by impact resistance) when 60 to 70% is in the heterogeneous state where some of the primary particles still exist in the crystalline melt matrix (12). It is this dependence on melt morphology -and the interdependence of modifier and PVC morphology-that makes ' a e modification of PVC different.Merz and his co-workers concluded that impact resistance developed from absorbing energy in the fracture of rubbery particles as cracks were propagated through them (13). Newman and Strella found this explanation unsatisfactory because the increase in energy absorption far exceeded tha...

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Dark time yellowing of white rigid vinyl outdoor weatherable compounds

Cited by 5 publications

References 16 publications

Accelerated Aging, Photochemical and Thermal Aspects

Accelerated Aging, Photochemical and Thermal Aspects

Gelbfäurbung von weißpigmentiertem PVC bei Dunkellagerung nach Bewitterung

Impact modifiers for PVC

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