Butyl rubber

Strict anaerobic techniques were thoroughly applied in this study. Sterile anoxic bottles were prepared as described in Text S2 (Supplementary Materials) prior to medium dispensing and inoculation. The gas volume/liquid volume ratio was maintained at three for all experiments, regardless of the size of the bottle, unless stated otherwise. The experiments were conducted with four biological replicates in the first stage (gas feeding of the anaerobic sludge) and triplicates in the second stage (enrichment in the mineral medium). A detailed chronology of the culture transfers is provided in Table S4.
The setup in the first stage was assembled in an anaerobic chamber. Serum bottles of 219.5 mL volume were filled with 50 mL degassed inoculum, sealed with butyl rubber stoppers and crimped with aluminum caps. The gas phase of the serum bottles was replaced by H₂ (80%) and CO₂ (20%). All bottles receiving H₂ and CO₂ were operated in fed-batch mode and pressurized daily to ~2.2 bar for approximately five months. Bottles containing the inoculum and a nitrogen atmosphere (not pressurized) were used as controls to account for the residual biogas production. Detailed information about headspace flushing and pressurization is given in Text S2.
In the second stage, medium A was used to enrich a particle-free culture by six subsequent culture transfers in fresh medium bottles by inoculating the content of the preceding culture transfer (10%, v/v). One randomly selected replicate from the first stage served as the inoculum to start the bottles for the second stage. Anoxic medium A (45 mL) was dispensed to sterile, anoxic serum bottles and left overnight in an incubator at 37 °C to reduce any oxygen traces that entered the bottles during medium dispensing. Next, the bottles were inoculated with 5 mL culture from the first stage. Biological controls for determining residual biogas production (containing inoculum but with N₂ gas phase), as well as sterile controls (not inoculated, but with either H₂/CO₂ or N₂ gas phase), were also set up. The bottles were fed with a gaseous substrate, as described above, and incubated at 37.4 °C in an orbital shaking incubator (IKA KS 4000 ic control, IKA^®-Werke GmbH & Co. KG, Biberach an der Riss, Germany) at 200 rpm.

The same amount additives were added to each sample with the sum mass of ZnO, stearic acid, TMTD, DM and S of 12.6 g when IIR was used 100 g. The rest amounts of the added reagents are shown in Table 1.Table 1

Formulation design of bio-based PF/NaH activation-modified butyl rubber damping material.

Sample code	IIR	Montmorillonite	LPF	NaH	DBA
IIR	100	–	–	–	–
IIR/M	100	40	–	–	–
IIR/M/LPF-10	100	40	10	–	–
IIR/M/LPF-15	100	40	15
IIR/M/LPF-20	100	40	20	–	–
IIR-6DBA/M/LPF-10	100	40	10	–	6
IIR-H2DBA/M/LPF-10	100	40	10	0.21	2
IIR-H4DBA/M/LPF-10	100	40	10	0.42	4
IIR-H6DBA/M/LPF-10	100	40	10	0.63	6
IIR-H8DBA/M/LPF-10	100	40	10	0.84	8
IIR-H10DBA/M/LPF-10	100	40	10	1.05	10

Stearic acid acts as a softening and plasticizing agent and facilitates the dispersion of other fillers. Zinc oxide acts as an activator of the rubber. TMTD and DM are rubber accelerators used to increase the rate of vulcanization of the rubber. Sulfur is used in the vulcanization of the rubber to cross-link the linear chains of rubber molecules into a network. Lignin phenolic resins are added to improve IIR related properties such as damping and tensility.
Figure 1 shows the flow chart for the synthesis of bio-based phenolic resins. In 250 mL three-necked flask equipped with stirrer, thermometer and reflux condenser, a certain proportion of phenol, NaOH and alkali lignin were respectively added and stirred well, and the temperature of the reaction system was raised to 90 °C and reacted for 90 min to obtain lignin phenol. The lignin mass accounted for 40% of the total mass of lignin and phenol, and the NaOH mass was 6% of the phenol mass. The reaction conditions of the lignin phenolic resin synthesis stage were consistent with the phenolic resin synthesis. When the temperature of the reaction system was reduced to 60 ℃, the formaldehyde was added, stirred uniformly and reacted for 60 min. After that, the temperature of the reaction system was increased to 90 ℃, and the reaction was carried out for 120 min with the molar mass ratio of phenol to formaldehyde of 1: 1.7. The reaction product was cooled to room temperature and then washed three times with respective anhydrous ethanol and deionized water in ultrasonic cleaner, and the product was finally put into vacuum oven and dried at 60 ℃ for 24 h. The product was dehydrated to obtain lignin phenolic resin (LPF).Figure 1

Synthesis of lignin phenolic resin.

Lignin was first phenolized by adding phenol under alkaline solution conditions, and formaldehyde was added under alkaline conditions after lignin was phenolized. Finally, the prepared bio-based phenolic resin was dried, crushed and kept for next preparation.
Figure 2 shows the flow chart for the preparation of damping composites. At a specific temperature, IIR and NaH were added into 60 mL Hacker’s torque rheometer, and after the torque time curve was stabilized, dibenzylidene fork acetone was added to continue the reaction for about 15 min (Fig. 3), and the modified rubber was obtained and set aside.Figure 2

Schematic diagram of the composite structure.

Figure 3

NaH activation modified IIR with introduced DBA.

The rubber added with dibenzyl fork acetone was plasticized on a double-roller opener, and the fillers stearic acid, zinc oxide, TMTD, DM, sulfur, lignin-based phenolic resin and montmorillonite were added in order and blended well. Stearic acid acted as softening and plasticizing agent and facilitated the dispersion of other fillers. Zinc oxide acted as activator of the rubber. TMTD and DM were rubber accelerators to increase the rate of vulcanization of the rubber. Sulfur was used in the rubber vulcanization to cross-link the linear chains of rubber molecules into network. Lignin phenolic resins were added to improve IIR related properties such as damping and ductility. The blended sample was left for 24 h to remove the air bubbles, and the raw rubber was prepared. Finally, 7–10 g of raw rubber was weighed and vulcanized on the plate vulcanizer to prepare the specimens of butyl rubber comprehensive temperature range damping composites. The vulcanization conditions were determined with vulcanization temperature of 160–170 ℃, vulcanization pressure of 10–12 MPa and vulcanization time of 14–18 min.
The isoprene monomer provides the molecular backbone of butyl rubber with an active point where the cross-linking reactions can take place. The most significant advantage of using reactive processing technology of rubber is that the chemical modification reaction can be carried out in general-purpose rubber processing equipment (e.g., torque rheometers, compactors). Short reaction process, simple preparation process and low experimental equipment requirements characterize this solvent-free ontology modification method. According to the principles of organic chemistry, sodium hydride does not react with alkanes. However, under certain conditions, it can react with hydrogen in the olefin double bond or the allyl position to produce carbon-negative ion. The typical reaction of carbon-negative ions is nucleophilic addition to compounds containing carbonyl groups^{26 (link)}. In this experiment, the NaH activator was selected to produce negative carbon ions on the molecular rubber chain. Then DBA, a compound containing carbonyl groups, was selected to introduce unsaturated double-bond functional groups and benzene rings with larger side groups to the main macromolecular chain. In the butyl rubber modification reaction process, the isobutylene structural unit is assumed not to participate in the reaction because the side methyl group on the isobutylene unit has low reactivity and does not participate in the reaction.