Parts per hundred resin

The effect of plasticizers and temperature on the permeabiUty of small molecules in a typical vinyUdene chloride copolymer has been studied thoroughly. The oxygen permeabiUty doubles with the addition of about 1.7 parts per hundred resin (phr) of common plasticizers, or a temperature increase of 8°C (91). The effects of temperature and plasticizer on the permeabiUty are shown in Figure 4. The moisture (water) vapor transmission rate (MVTR or WVTR) doubles with the addition of about 3.5 phr of common plasticizers (92). The dependence of the WVTR on temperature is a Htde more comphcated. WVTR is commonly reported at a constant difference in relative humidity and not at a constant partial pressure difference. WVTR is a mixed term that increases with increasing temperature because both the fundamental permeabiUty and the fundamental partial pressure at constant relative humidity increase. Carbon dioxide permeabiUty doubles with the addition of about 1.8 phr of common plasticizers, or a temperature increase of 7°C (93). 

Fig. 4. SmaH-angle x-ray scattering pattern from PVC plasticized with 20 parts per hundred resin of dioctyl phthalate (18).

Siding. The resin most used for siding is poly(vinyl chloride) homopolymer, compounded with modifiers, stabilizers, and pigments. Modifiers are most often acryhc esters, followed by chlorinated polyethylene or ethylene—vinyl acetate, used at 6—8 phr (parts per hundred resin). The modifier increases the impact strength of the rigid PVC. 

Low levels of ultraviolet absorbers (typically 0.2-0.8 pphr [parts per hundred resin]) can also be useful in preventing initiation of degradation mechanisms. Modified benzophenones and benzotriazoles are in widest commercial use. 

One inherent weakness of Vulkollan-type materials is their susceptibility to hydrolysis. Life in a humid environment may, however, be doubled by the incorporation of 2 pphr (parts per hundred resin) of a carbodiimide. 

Ingredient Parts by weight Parts per hundred resin (phr) % By weight... 

The adhesive used in this study consisted of Epon 828 (Shell Chemical Co.) cured with 10 phr (parts per hundred resin by weight) of triethylenetetraamine (TETA) (Fisher Scientific Co.). The resin was degassed in a vacuum oven at 50°C, combined with the curing agent, and then mixed for about I min using a magnetic stirrer. 

Fig. 4. Oxygen permeability in a vinylidene chloride copolymer film at selected levels of plasticizer (Citroflex A-4). Plasticizer level in parts per hundred resin...

PVAc Poly(vinyl acetate) phr. parts per hundred resin... 

Amines Room temperature or low-temperature cure Versamine (Cognis), Ancamine (Air Products), Aradur (Huntsman), and Epi-Cure (Hexion Specialty Chemicals) 1 15 parts per hundred resin (phr), fast gel times... 

PVB is plasticized for specific applications. Saflex contains 32phr (parts per hundred resin) of di-n-hexyl adipate. Butacite is PVB plasticized with 38.5 phr tetiaethylene glycol di-n-heptanoate. 

The most widely used epoxy resins are reaction products of either bisphenol A or a novolac phenolic resin with epichlorhydrin. When used to manufacture corrosion-resistant structures for use in the chemical process industry, epoxy resins are generally hardened with either aromatic or cycloaliphatic amines. The hardeners for epoxy resins are, with few exceptions, added at levels varying from 20phr (parts per hundred resin) to lOOphr. This means that the hardener is actually quite a high proportion of the matrix resin and has quite a profound effect on the mechanical and corrosion properties of the cured resin. Thus the selection of the most suitable hardener is critical to the eventual success of the application. Epoxy resins have viscosities of several thousand mPas at room temperature, which makes it much more difficult to wet out glass fibre efficiently with them than with polyesters. Wet-out therefore involves heating the resin formulation to between 40°C and 60°C to reduce the viscosity to less than 1000 mPas. 

A special grade meets the demand for halogen-free materials for pultruslon, resin transfer moulding, filament winding, and hand lay-up processes, giving highly retarded composites at a comparatively low addition rate. With this additive, at approximately 50 parts per hundred resin (phr), the Epiradiateur NF 92-501 test - one of the most stringent in Europe - can be passed with a classification of Ml, where 250 phr is required with aluminium hydroxide. With epoxy resins, the same low smoke density is produced as with polyester laminates, at addition levels of 20-50 phr. The aviation standard FAR 25.8 53 can be passed with an addition of 25-35 phr. A liquid-form additive is available where no powder additive can be used. 

In general, the concentration of the additive is represented by the mass fraction of additive per hundred mass fraction of resin, expressed as parts per hundred resin (PHR). The concentration of most additives is small, from a few tenths to several parts, some up to ten parts or more parts. 

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