Weatherable impact modifiers

Two general types of impact modified acryhc resins have been developed commercially, viz. (a) weatherable, impact modified, transparent acryhc resins for outdoor use in signs and automobiles ... 

The non-weatherable impact modified acrylic (XT, CYRO) typically consists of a MMA/S/AN copolymer with MBS (ca. 10%) rubber particle dispersions. 

Dow (2010) Polaroid BPM-520 Impact Modifier Weatherable Impact Modifier for Engineering Resins, http //www. dow.com/assets/attachments/business/ plastics additives/paraloid exl/ paraloid exl-2314/tds/paraloid exl-2314.pdf (accessed 05 November 2013). 

S-type Silicone-acrylic weatherable impact modifier S-2001... 

W-type Acrylic weatherable impact modifier W-300A (High transparent type)... 

Tab. 14-5 Commonly used commercial weatherable impact modifiers.

Tab. 14-7 Commonly used commercial non-weatherable impact modifiers.

The ASA used exhibits special characteristics with respect to mechanical properties. Naturally, a high resistance to weathering is required. An example for an impact modified weatherable, copolymer with resistance to weathering, aging, and yellowing, is Luran S 776. 

It has high modulus, strength, and resistance to creep, weathering, and chemicals and compounding with rubbery impact modifier produces high resistance to brittle failure. It is mainly extruded into pipe, house-siding, and... 

CPE impact modifiers contain around 35% of chlorine and are thermoplastic in nature. With a similar melting point to PVC, they initially form a network structure which changes to a particulate structure on processing (134). They also have good processability and excellent weathering performance consequently they are also used for window profiles (287). The effect of residual... 

Particle size is important and, for some applications requiring good weathering and impact performance (window profile), the ultrafine milled, high whiteness, natural version is normally used. To ease dispersion, the filler is usually coated with stearic acid. Coated ultrafine and precipitated calcium carbonates are claimed also to have a positive effect on impact properties in impact modified formulations (52, 294, 462). The abrasive wear of calcium carbonate, on melt processing equipment, is not significant but increases with increasing levels (177). 

The largest group comprises the impact modified PEST s — these were summarized while discussing commodity resin blends. The commercial blends with, e.g., SMA or acrylic rubber, show good processability, rigidity, impact and tensile strength, as well as excellent weatherability, viz. Arloy 2000, Bexloy , Celanex , Pibiter HI, Rynite , Ultradur KR. 

PEST Blends PET with PDMS and MABS PEST and/or PC with siloxane-based vinyl-grafted copolymer PEST/PC/PPE/star-block copolymer PEST and siloxane-acrylic elastomer impact and embrittlement resistance chemical, weather, and low temperature impact resistance impact modified engineering resins impact strength at low temperature Sauers Barth, 1970 Kongo et al., 1987 Hoxmeier, 1994 Yamamoto eta/., 1992, 1994... 

However, they can also be transfer or compression molded, solid state formed or thermoformed. PC is the matrix phase in most of these blends. The impact modifier can be PE, ABS or acrylic copolymer, e.g., MBS. The blends show good processability, heat resistance, ductility, HDT, high modulus, impact, tensile and flexural strength over a wide temperature range, good adhesion, solvent, chemical, and UV resistance. They can be painted, hot stamped, metallized and plated. Some blends (containing PB as impact modifier) may have poor weatherability. The blends are mainly used in the automotive industry. 

Desirable blend properties are impact strength (withstand drop test at -29°C), solvent resistance and weatherability. Blends predominantly used include impact-modified PA (6 and 66), PC/PEST and PC/ABS. 

Impact Modifiers Improving impact properties, melt index, processibility, weatherability. ... 

Impact modifiers help to improve impact properties by toughening the system, as well as improving the melt index, processability and weatherability. 

As an example, rigid PVC provides an excellent cost/performance balance with inherent flame retardancy. It is used particularly in building and construction applications such as window frames, doors, fencing and plumbing, but it needs improvement in some mechanical and weatherability properties, which is achieved by use of an acrylic-styrene or a butadiene-based, rubbery impact modifier. 

Predesigned particles of impact modifiers are based on core-shell technology. Core is involved in impact modification and shell improves adhesion between PVC and impact modifier particles.Three major combinations are used methacrylate-butadiene-styrene, MBS, which has a core made out of butadiene-styrene copolymers and shell made out of methylmethacrylate-styrene copolymer, acrylic impact modifiers, AIM, which have a core made out of acrylic and shell from polymethylmethacrylate, and silicone-acrylic have multilayer structures with silicone-acrylic in the core. MBS has excellent compatibility with PVC, similar to ABS, which is used as an impact modifier of PVC, as well. In both cases of ABS and MBS, weather resistance is lacking, therefore they are used for indoor applications only. At the same time, MBS gives translucent to crystal clear products, whereas with AIM, only translucent products are possible. In order to improve optical properties of AIM, it has to be reformulated. For transparent products, the core is made out of acrylic-styrene copolymers. Comparing silicone and all acrylic impact modifiers, PVC containing silicone-based products has superior low temperature impact properties. The incorporation of silicone into an acrylic impact modifier provides excellent weatherability, and thermal stability. It has shown improved retention of impact after outdoor weathering in PVC. ... 

EPDM Rubber Sulfur-vulcanizable thermosetting elastomer produced from ethylene, propylene, and a small amount of nonconjugated diene such as hexadiene. Has good weatherability and chemical and heat resistance. Used as impact modifiers and for weather stripping, auto parts, cable insulation, conveyor belts, hoses, and tubing. Also called EPDM. 

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