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PMMA – a leader among transparent polymers  #7-8 (53-54), 2007

Each year Russian thermoplastics market grows by 15-20%. Out of total amount of polymers consumed, transparent polymers, that answer highest requirements to optical light-transmitting properties, can be specifically distinguished

Transparent thermoplastics are polymer-based materials that are optically transparent and can be given the desirable shape by heating and injection molding or profile extrusion. They can contain additives, plasticizers, stabilizers, pigments, lubricants and other components. They provide broader application for this type of polymers in making manifold products. Thus, by adding filling agents it’s possible to get a partially transparent or light-divergent material. This makes the material suitable for lighting engineering. Most well-known thermoplastics here are polystyrene (PS), styrene acrylonitrile (SAN), polymethyl methacrylate (PMMA) and polycarbonate (PC).
Recommendations for processing granulated Дакрил® PMMA by injection molding
For the process the following parameters are set: Tmt (melt temperature), Tmd (mold temperature) and Q - injection bulk speed (or time needed for mold’s filling). Advisory set parameters for injection molding: Tmt is 200-230oC, Tmd is 40-80oC, specific injection pressure is 100-160 MPa, differential temperature between neighbouring zones of the cylinder – 5-10oC.
Product’s temperature right after removing from the mold must be not higher than glass transition temperature, that makes 90-110oC depending on the brand, in order to guarantee the needed rigidity at mold’s opening.
Mold’s temperature in relation to melt’s temperature defines the speed of melt’s cooling when it fills in the mold. This influences orientation of polymers in the surface layer, and, consequently, on the mechanical strength of the product.
For eliminating internal stresses that can cause cracks, it’s recommended to expose finished articles to burn-in (conditioning at 50-80oC) for several hours.
Often it’s hard for a consumer to choose the best alternative and to see the in what way the materials differ. By this article we want to help you to choose the best materials for your production. Major characteristics of transparent materials are compared at picture 1.
It’s important to mention that compared with cheaper styrene polymers like PS and SAN, PMMA is a feedstock of different level. Products made of PMMA are glossy, smooth to the touch, have most robust outer layer and thus better scratch-resistance. It’s also important that in case scratch appears it’s possible to polish the surface. PMMA can be exposed to low temperatures up to -60?C and is chemical resistant, particularly – contrary to PC – to automobile fuels.
Though there are thermo- and light-stabilized brands of PC and PS, they can never be as resistant to atmosphere phenomena as PMMA, retaining its optical and mechanical properties for 10 years.
That is why most light engineering and optical production manufacturers all over the world prefer PMMA.
PMMA fields of application can be divided into tow main groups:
- automobile lighting (lens, decorative moldings, button lights and dashboard protective glasses);
- lighting devices for consumer and industrial use (diffusers).
PMMA is an amorphous thermoplastic with density rate of 1180-1200 kg/m3 . As it was mentioned above, this material is quite resistant to light and atmosphere effects, and in this aspect exceeds most other thermoplastics. This accounts for material’s long life always retaining its main properties.
Principal characteristics of transparent materials, comparedThere are numerous PMMA producers in Europe, America and Asia who make it under various trade names. In Russia most popular brands are Plexiglass® (Degussa), Altuglas® (Arkema) and Дакрил® (JSC Dzerzhinskoye orgsteklo).
JSC Dzerzhinskoye orgsteklo (JSC DOS) is the only producer in Russia in making granulated PMMA and has a working experience of 40 years. Today JSC DOS manufactures broad range of granulated PMMA under brand name Дакрил® for various purposes. Дакрил® properties are given in table 1.
The parameter distinguishing one brand from another is melt flow rate, defining the area of application. The higher is the MFR, the more complex shape product is allows to produce, including products with large surface. In this connection DOS’s PMMA brands are divided into two groups: recommended for injection molding and recommended for (co)extrusion (see table 1). DOS also makes special brands (Дакрил® КАУ-1Л,-1Э) with enhanced impact resistance and elasticity, which broadens application alternatives for PMMA.
High degree of transparency and full color absence make parts and semi-finished products made of Дакрил® transmit 92% of light. Due to absolute color neutrality it’s possible to achieve very pure shade after coloring, and give the material exactly the shade you want. Orange and red Дакрил® is used for automobile lighting devices, and white light-divergent Дакрил® – for home and industrial lighting technique.
Thus, in all spheres where saturated color, high degree of transparency, unsurpassed resistance to atmosphere effects and outstanding surface properties are needed, Dacryle® PMMA is the only material that can guarantee meeting all these requirements.

Table 1. Дакрил PMMA properties

Brand  Melt flow rate (230oC/3.8 kg)  Tensile strength, MPa, no less than  Stretch ratio, %, no less than  Charpy impact strength, kJ/m2, no less than  Vicat softening temperature, oC, no less than

 Recommended for injection molding

Дакрил®-61 8,0 - 15,0  60 4,0 16  90
Дакрил®-71  4,0 - 6,0  70 6,0  16 100
Дакрил®-81  2,5 - 3,5 76 6,0  16 108

 Recommended for (co)extrusion

 Дакрил®-72  1,5 - 4,0  70 6,0  16  100
 Дакрил®-82  1,0 - 2,5 78 6,5  16 108

 Special brands (enhanced elasticity and impact strength)

 Дакрил®-КАУ-1Л  1,8 - 3,0 65 25,0 30 100
 Дакрил®-КАУ-1Э 1,0 - 2,0 65 25,0 30 100

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