Natural Rubber Composites Using Hydrothermally Carbonized Hardwood Waste Biomass as a Partial Reinforcing Filler- Part I: Structure, Morphology, and Rheological Effects during Vulcanization

Abstract

A new generation biomass-based filler for natural rubber, ‘hydrochar’ (HC), was obtained by hydrothermal carbonization of hardwood waste (sawdust). It was intended as a potential partial replacement for the traditional carbon black (CB) filler. The HC particles were found (TEM) to be much larger (and less regular) than CB: 0.5–3 µm vs. 30–60 nm, but the specific surface areas were relatively close to each other (HC: 21.4 m2/g vs. CB: 77.8 m2/g), indicating a considerable porosity of HC. The carbon content of HC was 71%, up from 46% in sawdust feed. FTIR and 13C-NMR analyses indicated that HC preserved its organic character, but it strongly differs from both lignin and cellulose. Experimental rubber nanocomposites were prepared, in which the content of the combined fillers was set at 50 phr (31 wt.%), while the HC/CB ratios were varied between 40/10 and 0/50. Morphology investigations proved a fairly even distribution of HC and CB, as well as the disappearance of bubbles after vulcanization. Vulcanization rheology tests demonstrated that the HC filler does not hinder the process, but it significantly influences vulcanization chemistry, canceling scorch time on one hand and slowing down the reaction on the other. Generally, the results suggest that rubber composites in which 10–20 phr of CB are replaced by HC might be promising materials. The use of HC in the rubber industry would represent a high-tonnage application for hardwood waste.

Natural Rubber Composites Using Hydrothermally Carbonized Hardwood Waste Biomass as a Partial Reinforcing Filler—Part II: Mechanical, Thermal and Ageing (Chemical) Properties

“…This work aimed to investigate the potential of bio-sourced hydrochar (HC) for the role of carbonaceous filler in elastomeric composites, specifically in composites with natural rubber as a matrix, similar to rubber composites used in tires. The hydrochar (HC) was obtained from sawdust waste via the modern hydrothermal carbonization method (HTC), adjusted by the authors, and followed by ball milling, as described in detail in the first part of this broader work [ 27 ]. For evaluating the HC-based nanocomposites, a classical tire rubber recipe (natural rubber + filler phase + vulcanization accelerator ZnO + stearic acid as a dispersion agent for ZnO + CBS as vulcanization accelerator with delayed action + sulfur as crosslinker + IPPD as anti-oxidant and anti-ozonant; details: see Table 1 in the Experimental Part, Section 2.3 ), which contained 50 phr (31.5 wt.%) of carbon black (CB) as the filler phase, was modified.…”

“…It can be noted that the co-fillers strongly differ in their size: HC (irregular particles: relatively light grey in Figure 1 c,d, and darker in Figure 1 b) displays sizes between 0.5 and 3 µm, while the diameter of CB (very dark small spheres) ranges from 30 to 60 nm. Both nanofillers were extensively characterized in the mentioned previous work [ 27 ]. The BET surface areas were found to be 77.8 m 2 /g and 21.4 m 2 /g for CB and HC, respectively.…”

“…In a previous paper, which is the first part of the wider presented work [ 27 ], the authors applied their own brief HTC treatment method to sawdust originating from the oak tree. A comprehensive characterization of the so-obtained HC filler was undertaken, including some aspects of blending the obtained HC with natural rubber.…”

“…The aim of the authors’ present work was to assess the suitability of the bio-sourced hydrochar (HC) , obtained according to [ 27 ], as a filler (or co-filler) in natural rubber and similar elastomers. For this purpose, a standard rubber recipe was modified by partially (and even fully) substituting the classical CB filler with HC while the loading of the co-fillers phase was kept constant.…”

The comparative study of biocomposites based on hydrochar and chitosan‐modified urea‐formaldehyde resins

“…It was added to the rubber to replace the traditional carbon black without affecting the original properties of the rubber. [ 35 ] It was also used in the PLA/hydrochar biocomposites, where it contributed to the improvement of mechanical and thermal properties. [ 36 ] But, based on the available literature, there is no data on UF resins modified with hydrochar as filler, which represents a completely new approach.…”