Knowde Enhanced TDS
Identification & Functionality
- Chemical Family
- Polymer Name
- Plastics & Elastomers Functions
- Technologies
- Product Families
Features & Benefits
- Materials Features
- Product Information
Conventional and linear polyethylenes have a wide range of excellent properties and they are both readily processed by rotational molding. Both these types of polyethylene are made up of long polymeric chains that are closely entangled in a complex structure. The state of this structure forms the basis of the performance properties of articles made from each particular grade or type of polyethylene. Polyethylene always remains thermoplastic, which means that the application of heat will cause the polymer chains to move and the entangled chain structure to become distorted. Melting or softening occurs and the finished product becomes unusable. Other aggressive environments such as impact loads, aggressive chemicals, low temperatures and environmental stresses cause the entanglement of the polymer chains to change leading to destruction of the polymeric structure. Creation of links between the polymer chains prevents movement of the chains in relation to one and another thus forming a more stable polymeric structure. The process of making crosslinkable polyethylene involves firstly the formation of sites on the polymer chains where links can be initiated. The second stage of the process is the development of strong, permanent three dimensional links between the chains. The final result is a more rigid and stable polymeric structure within the finished molding that will have enhanced resistance to a wide range of aggressive environments or rigorous service conditions that would destroy conventional or linear polyethylenes. Micropol have been producing crosslinkable polyethylene for extrusion for more than 25 years. We have also been producing color compounded rotational molding powders for 40 years. Our extensive experience of these technologies has been combined to produce a unique range of color compounded crosslinkable powders for rotational molding.
Applications & Uses
- Applications
- Plastics & Elastomers End Uses
- Plastics & Elastomers Processing Methods
- Processing
- PROCESSING AND TESTING: Microlink XL is rotationally molded by methods largely similar to those used in processing conventional and linear polyethylene.
- MOLD CONSTRUCTION: Steel and aluminum molds are both suitable. Molds should not have porous interior surfaces and must be well vented to relieve the pressure build up generated during the heating cycle. Particular attention should be paid to the design and use of the vent tube to ensure that it does not become clogged with powder or molten polymer.
- PROCESSING CONDITIONS: As with other polyethylenes, processing conditions will vary according to the machinery used (particularly the oven design and control) and the molding being produced. As a general rule processing temperatures of between 270°C and 300°C have been found suitable. Heating time is of the order of 4 minutes per millimeter of wall thickness. In order to complete the crosslinking reaction which occurs during the heating cycle, sufficient heating time has to be allowed. As the molding temperature is raised the chemical crosslinking will proceed more rapidly, and a shorter heating cycle may be possible. Satisfactory moldings may thus be made at various combinations of molding temperature and time, these two parameters being linked together.
- TESTING DEGREE OF CROSSLINKING: In order to assess whether the selected combination of heating time and temperature is sufficient to have completed the crosslinking reaction, certain tests can be carried out. These will give a useful indication of the degree of crosslinking achieved. Test failure usually means that heating time or temperature needs to be increased.
- BENT STRIP TEST: A narrow strip (10-20mm wide) is cut from the part or trim and bent so that the inside surface is on the outside of the bend. Appreciable surface crazing with cracks going into the wall interior indicates that the part is not completely crosslinked.
- FALLING WEIGHT IMPACT TEST: In this test a 4.5 kg weight metal dart having a hemispherical striker is dropped from a predetermined height on to a 150mm square sample cut from the molding. The sample is cooled before testing to - 20°C. Insufficient crosslinking results in brittle failure in the test piece. This test is based on one devised by "The Association of Rotational Molders". Full details can be obtained from Micropol.
- GEL CONTENT BY EXTRACTION: In this test the non crosslinked fraction of the part is dissolved in boiling xylene under reflux. The remainder is dried and weighed and the actual crosslinking percentage determined. Micropol Technical Service Laboratory is fully equipped to carry out this and other tests on behalf of customers and can also advise on the exact test methods.
- DENSITY Uncrosslinked XL28: has a density of 0.964 g/cm3. During crosslinking the density becomes lower until the fully crosslinked material has a density of 0.938 g/cm3. This change in density with crosslinking can be used to assess the extent of the crosslinking reaction.
- colorED MICROLINK XL: The wide spectrum of colors available in MICROLINK XL are all color compounded. We will color match your specially required color using only the most stable and toxicologically acceptable pigments. We have an extensive and increasing range of color formulations designed to meet customers' increasing demands. The appearance of moldings made from compounded MICROLINK is the best possible regarding depth, iformity and stability of color. The standard of all aspects of color quality is comparable with that achieved with the highest quality of injection molding processes. The problems of poor pigment dispersions associated with dry coloring are totally overcome by the use of Micropol's high specification color compounding processes. The availability of color compounded MICROLINK XL offers the molder many advantages:- 1. No in-plant color mixing. 2. No stock holding of a multitude of expensive pigments or pigment packs. 3. No color variation between moldings. 4. No moldings with poor pigment dispersion. 5. No large stock holding of natural powder, nor excessive quantities of colored powder, just the specific quantity of colored powder for each order. The greatest advantage to the molder is that we carry out the total color process and deliver to your plant colored crosslinkable polyethylene powder ready to be loaded into the mold. NATURAL AND BLACK ARE ALSO AVAILABLE.
Properties
- Physical Properties
| Value | Units | Test Method / Conditions | |
| DENSITY | 0.938 | g/cm³ | D1505 |
| ESCR (F50) | min. 1000 | Hours | D1693 |
| ULTIMATE TENSILE STRENGTH (50mm/min) | 23 | MPa | D638 |
| ELONGATION AT BREAK | 350 | % | D638 |
| VICAT SOFTENING TEMPERATURE | 127 | ºC | D1525 |
| BRITTLENESS TEMPERATURE | max.-70 | ºC | D746 |
| FLEXURAL MODULUS | 750 | MPa | D790 |
| IMPACT RESISTANCE* AT -20ºC | 36 | Joules/mm | Micropol test method, based on ASTM D1709 |
Safety & Health
- SAFETY AND HANDLING PRECAUTIONS
Microlink XL contains crosslinking agents (including peroxides) which may cause skin, eye or respiratory irritation during powder handling or thermal processing. When molds are being loaded with powder inhalation of dust and contact of dust with the skin should be prevented. Local exhaust systems are recommended in processing areas and the use of a vacuum lance for removing decomposition products prior to mold opening should be considered. Goggles, gloves and dust masks should be worn when handling powder and a daily change of working clothes.