Biocomposites Based on Polyamide 11/Diatoms with Different Sized Frustules

Abstract

Amorphous diatomite containing approx. 80% silicon dioxide SiO2 was used as a filler for a thermoplastic polymer of polyamide 11 obtained from natural sources. The diatomite particles of different sizes were previously fractionated by sedimentation to obtain powders with varying particle size distribution, including powders with or without frustule particles, crushed, uncrushed or agglomerated. Biocomposites containing 2.5, 5, 10 and 20% filler were tested for their mechanical properties, including tensile strength, flexural strength and impact strength. In addition, a particle size analysis (by Dynamic Light Scattering, DLS) was performed and the dispersion of the filler in the polymer matrix (Scanning Electron Microscopy, SEM), thermal parameters (Differential Scanning Calorimetry, DSC, and Dynamic Mechanical Analysis, DMA) were determined. Testing showed that biocomposites modified with diatomaceous earth have a higher mechanical strength than the reference system, especially with larger amounts of the filler (10 and 20%), e.g., the tensile strength of pure PA11 is about 46 MPa, while 20OB and 20OF 47.5 and 47 MPa, respectively, while an increase in max. flexural strength and flexural modulus is also observed compared to pure PA11 by a maximum of 63 and 54%, respectively Diatomaceous earth can be obtained in various ways—it is commercially available or it is possible to breed diatoms in laboratory conditions, while the use of commercially available diatomite, which contains diatoms of different sizes, eliminates the possibility of controlling mechanical parameters by filling biocomposites with a filler with the desired particle size distribution, and diatom breeding is not possible on an industrial scale. Our proposed biocomposite based on fractionated diatomaceous earth using a sedimentation process addresses the current need to produce biocomposite materials from natural sources, and moreover, the nature of the process, due to its simplicity, can be successfully used on an industrial scale.

Polyamide 11 Composites Reinforced with Diatomite Biofiller—Mechanical, Rheological and Crystallization Properties

“…It was found that the addition of diatomite did not affect T g or T m to any significant extent. On the other hand, in the previous work [ 30 ], a more significant drop in T g was observed upon the addition of diatomite, showing that untreated diatomite presence causes formation of a filler–matrix interphase of weak interaction, with additional polymer freedom, while the filler treatment with APTES increases this interaction. The addition of diatomite caused a slight increase in the crystallisation temperature, showing some nucleation properties of the filler; however, silanization thereof caused no difference in this matter.…”

“…The notch impact test was conducted for the composites both with the addition of silane and, comparatively, without silane, which was presented previously in [ 30 ]. Neat polyamide was characterised by the highest impact strength amongst the tested samples, 7 kJ/m 2 ( Figure 6 ).…”

“…The fractionation of amorphic diatomaceous earth was performed using the hydraulic method, according to the procedure presented in previous works [ 30 , 31 ], with the use of gravitational sedimentation. Fifteen kilograms of amorphic diatomaceous earth (particle size between 1 μm and 100 μm) was washed with demineralised water in order to separate particles of different sizes.…”

“…The parameters of the measurements for the wet samples were a stirrer revolution speed of 2330 RPM and an ultrasound power of 70%. The tensile, bending and impact strength tests, rheological tests (MFR, viscosity), thermal tests (DSC, DMTA) and microscope observations were compared to the composites produced by direct injection moulding, which are described in a previous paper [ 30 ]. Additionally, the tests were complemented with a surface analysis, that is, the analysis of wetting angle and the test of gloss at the composite surface for all samples, whether or not they were modified by the APTES.…”

“…The degree of dispersion of a filler in a polymer was determined using a scanning electron microscope. Our reference systems were the composites produced in a previous work [ 30 ], which made it possible to fully specify the impact of both the diatomaceous earth alone and the silanized diatomaceous earth on the characteristics of the obtained composites.…”