Poly(ε-Caprolactone)/Brewers’ Spent Grain Composites—The Impact of Filler Treatment on the Mechanical Performance

Aleksander Hejna

doi:10.3390/jcs4040167

Abstract

Waste lignocellulose materials, such as brewers’ spent grain, can be considered very promising sources of fillers for the manufacturing of natural fiber composites. Nevertheless, due to the chemical structure differences between polymer matrices and brewers’ spent grain, filler treatment should be included. The presented work aimed to investigate the impact of fillers’ reactive extrusion on the chemical structure and the poly(ε-caprolactone)/brewers’ spent grain composites’ mechanical performance. The chemical structure was analyzed by Fourier-transform infrared spectroscopy, while the mechanical performance of composites was assessed by static tensile tests and dynamic mechanical analysis. Depending on the filler pretreatment, composites with different mechanical properties were obtained. Nevertheless, the increase in pretreatment temperature resulted in the increased interface surface area of filler, which enhanced composites’ toughness. As a result, composites were able to withstand a higher amount of stress before failure. The mechanical tests also indicated a drop in the adhesion factor, pointing to enhanced interfacial interactions for higher pretreatment temperatures. The presented work showed that reactive extrusion could be considered an auspicious method for lignocellulose filler modification, which could be tailored to obtain composites with desired properties.

Highlights

From an economical and, most of all, the ecological point of view, one of the most beneficial approaches towards manufacturing natural fiber composites (NFCs) is applying various by-products or waste materials as reinforcements [1]
Obtained Fourier-transform infrared spectroscopy (FTIR) spectra are very similar to spectra obtained by other researchers for isolated melanoidins [24], which suggests that melanoidins were generated during modification of brewers’ spent grain (BSG)
In the range of 2850–2950 cm−1, there are observed signals associated with the symmetric and asymmetric stretching vibrations of C-H bonds in methyl and methylene groups. They are present in the polymer matrix, as well as carbohydrate structures of BSG

Summary

Introduction

Most of all, the ecological point of view, one of the most beneficial approaches towards manufacturing natural fiber composites (NFCs) is applying various by-products or waste materials as reinforcements [1]. Multiple approaches aimed at the enhancement of interfacial interactions were analyzed They included modifications of polymer matrices, incorporation of additional compatibilizers, or various filler treatments [12]. Considering current pro-ecological trends and economic factors, it is very beneficial to reduce the number of steps required to manufacture polymer composites and simplify the whole production process Such an approach could reduce the amount of generated waste and reduce the use of energy or water. It is very beneficial to introduce unit processes with continuous character, instead of periodic character [13] Considering these issues, properly designed filler treatment seems to be the most promising solution for the enhancement of interfacial adhesion in composites. The presented work aimed to investigate the impact of filler treatment on its particle size and chemical structure and the mechanical performance of the poly(ε-caprolactone)/brewers’ spent grain composites. The impact of melanoidins, generated during the thermo-mechanical treatment of brewers’ spent grain, on the mechanical performance of the resulting composites, has not been investigated yet

Materials

Extrusion Grinding of BSG

Measurements

Spectroscopic Analysis

Physico-Mechanical Properties

Conclusions