Properties of Moldings Prepared from LDPE-Pumpkin Seed Hulls Blend

Abstract

In recent decades, standard polymer blends for different applications have been more and more often replaced by blends containing raw materials. The use of natural materials as filler in thermoplastics brings both economic and environmental benefits. The use of a given vegetable filler depends on the geographic location and natural occurrence of the vegetables in a given geographic region. In Poland, for instance, the pumpkin is one of such vegetables. They are used for producing oil which is pressed from pumpkin seeds. Pumpkin seeds are then collected, dried and purified to produce waste material in hull form. Particles of ground pumpkin seed hulls with varying sizes and weight-in-weight concentration ranging from 0% to 20% relative to the matrix are used as filler in low-density polyethylene. Pumpkin seed hulls are ground and sieved. Four fractions of hulls with different particle sizes are produced: <0.2 mm, 0.2-0.4 mm, 0.4-0.6 mm, 0.6-0.8 mm. The paper reports the results of investigation of the mechanical properties, i.e., strength properties determined by static tensile testing and hardness measurement, of injection molds produced at constant processing parameters. In addition, the cross sections of the obtained products are subjected to microscopic examination. Relationships are determined between tensile modulus, maximum tensile stress, tensile stress at yield, maximum tensile strain, tensile strain at yield as well as Shore hardness and weigh-in-weight concentration of the powdered natural filler and its grain sizes. Finally, relevant conclusions are drawn.

Impact of Intensive Mixing and Shearing Elements on the Effectiveness of Extrusion of Wood Polypropylene Composites

“…Polymer processing techniques are rapidly developing these days. The extrusion and injection molding process plays a very important role in polymer processing and are the most widely used methods for processing polymers [1][2][3]. There are diff erent types of extrusion processes, such as conventional extrusion, autothermal extrusion, extrusion coating, blown fi lm extrusion, and many others [4][5][6].…”

“…In polymer processing, phenomena occurring in the plasticizing system are of great importance for extrusion process eff ectiveness [7]. The plasticizing system performs several important functions, including heating, compression, mixing and conveyance [3]. Technological conditions of the extrusion process and the design of the extruder plasticizing system play a key role in polymer extrusion, too.…”

“…This is due to the fact that these elements have a crucial impact on the fl ow rate of a polymeric material, energy consumption of the extrusion process, and the desired quality of the extrudate. Polymer mixing is a key operation in extrusion [3]. Mixing is used to homogenize the composition and properties (predominantly frictional and mechanical) of a processed polymer, as well as to homogenize its structure [8][9][10][11].…”

“…A pineapple mixing section is an example of high shear elements that primarily exhibit distributive mixing characteristics. Examples of elements that are predominantly used for dispersive mixing include blister rings or grooved elements such as the Maddock [8,10], Maillefer or Barr style mixers [3]. The mixing process can be predominantly intensified by sequence-type dividing of the streams of polymer and combining them subsequently as well as by rotating these streams.…”