E N T E C P O L Y M E R S | 1 9 0 0 S u m m i t T o w e r B l v d . , S u i t e 9 0 0 | O r l a n d o , F L 3 2 8 1 0 | P : 8 3 3 . 6 0 9 . 5 7 0 3 | E n t e c P o l y m e r s . c o m

9/30/2019The information presented in this document was assembled from literature of the resin product producer(s). The information is believed to be accurate however Entec Polymers (“Entec”) makes no representations as to its accuracy and assumes no obligation or liability for the information, including without limitation its content, any advice giv-en, or the results obtained. ENTEC DISCLAIMS ALL WARRANTIES, EXPRESSED OR IMPLIED, INCLUDING FITNESS FOR A PARTICULAR PURPOSE. The customer shall use its own independent skill and expertise in the evaluation of the resin. product to determine suitability for a particular application and accepts the results at its sole risk.

THE DIFFERENT TYPES OF POLYETHYLENE RESINS FOR ROTATIONAL MOLDING

E N T E C P O L Y M E R S | 1 9 0 0 S u m m i t T o w e r B l v d . , S u i t e 9 0 0 | O r l a n d o , F L 3 2 8 1 0 | P : 8 3 3 . 6 0 9 . 5 7 0 3 | E n t e c P o l y m e r s . c o m

THE DIFFERENT TYPES OF POLYETHYLENE RESINS FOR ROTATIONAL MOLDING

9/30/2019The information presented in this document was assembled from literature of the resin product producer(s). The information is believed to be accurate however Entec Polymers (“Entec”) makes no representations as to its accuracy and assumes no obligation or liability for the information, including without limitation its content, any advice giv-en, or the results obtained. ENTEC DISCLAIMS ALL WARRANTIES, EXPRESSED OR IMPLIED, INCLUDING FITNESS FOR A PARTICULAR PURPOSE. The customer shall use its own independent skill and expertise in the evaluation of the resin. product to determine suitability for a particular application and accepts the results at its sole risk.

▶ Low Density Polyethylene (LDPE) is flexible and tough, easy to process, has excellent warp resistance and consistent shrinkage. Low Density Polyethylene range from 0.925 g/cm³ and lower. LDPE resins are typically used in toys and consumer products that don’t require a lot of stiffness or load carrying ability. Disadvantages would be that it has both low stiffness and low environmental stress crack resistance (ESCR).

▶ Linear Low Density Polyethylene (LLDPE) or Medium Density Polyethylene (MDPE) resins have better mechanical properties than LDPE as well as higher stiffness, good warp resistance, excellent low temperature impact strength and excellent environmental stress crack resistance. Medium Density Resins range from 0.926 g/cm³ to 0.940 g/cm³. MDPE resins are typically used in recreational, consumer or agricultural goods that require the higher temperature resistance or stiffness that low density resins do not provide. Disadvantages would be that these are less stiff than HDPE and have a lower temperature resistance.

▶ High Density Polyethylene (HDPE) is the stiffest resin of the polyethylene family. HDPE has excellent chemical resistance, higher heat deflection temperature and good processability and impact strength. High Density Resins range from 0.941 g/cm³ to 0.959 g/cm³. HDPE resins are typically used in recreational and consumer products, bulk containers, marine products and also agricultural and chemical storage tanks. Disadvantages would be that these resins have low ESCR and warpage/shrinkage is not as consistent.

In Rotational Molding, a resin needs to have very good flow when molten. With polyethylene, the flow is measured by the melt index. The higher the melt index, the better the flow. Most standard rotomolding resins have melt flow specifications ranging from 2g/10 minutes to 7g/10 minutes. The term “g/10 minutes” refers to the weight of molten resin moving through an orifice of a predetermined size in 10 minutes.

MELT INDEX

Density is a measure of the specific gravity of a resin. The density of polyethylene is classified by types such as LDPE, MDPE and HDPE according to the American Society of Testing and Materials (ASTM). In addition to increasing the overall stiffness of a part, increasing density raises the melting point, permits higher operating temperature limits and improves barrier properties in the end product.

DENSITY

What happens when you increase the Melt Index or Density of a resin?

1. Melting Point

2. Flow

3. Impact Strength

4. Stiffness

5. Vicat Softening Temp

6. Resistance to Low Temp Brittleness

7. Barrier Properties

AN INCREASE IN MELT INDEX DENSITY

Increases

Remains The Same

Decreases

Increases

Increases

Decreases

Increases

Remains The Same

Increases

Decreases

Remains The Same

Decreases

Decreases

Remains The Same