Seiichi Kawahara

Buoyancy-driven latex purification - a sustainable and low-energy method successfully prepared protein-free natural rubber (PFNR). The development of environmentally friendly PFNR production is increasingly important due to the growing demand for allergy-safe natural rubber materials in medical and biomedical applications, including surgical gloves, catheters, balloons, and related devices. Conventional purification methods require repeated centrifugation cycles with high electricity consumption, leading to significant operational costs and indirect CO2 emissions, particularly in major natural rubber-producing countries where electricity generation relies heavily on fossil fuels. This study presents a method for producing PFNR through a combination of salting-out techniques, saponification, and protein denaturation. High-ammonia natural rubber (HANR) latex is treated with NaOH, SDS, and urea, followed by the buoyancy-driven latex purification using CO2 bubbling. Nitrogen content, representing residual protein amounts, was determined by the Kjeldahl method, while fatty acid ester content was evaluated using FT-IR spectroscopy. The chemical structure was examined by 1H NMR spectroscopy. Particle size distribution and zeta potential were measured to examine colloidal stability and flocculation behavior. Mechanical properties were assessed by tensile testing of unvulcanized rubber samples. Contents of nitrogen and fatty acid esters were reduced from 0.194 w/w% and 24.3 mmol/kg rubber for HANR to 0.000 w/w% and 15.6 mmol/kg rubber for PFNR, respectively. 1H NMR analysis showed that high stereoregularity was maintained after the buoyancy-driven latex purification. Tensile strength of unvulcanized PFNR film was lower than that of HANR film due to the removal of proteins and lipids.

The present work aimed to develop a novel deproteinized natural rubber (DPNR) composite reinforced with microcrystalline cellulose grafted with poly­(trimethylene carbonate) (MCC-g-PTMC). The hypothesis is that the amorphous and flexible PTMC chains improve the compatibility between MCC and DPNR, thereby enhancing mechanical properties. To verify this, MCC-g-PTMC was synthesized by ring-opening polymerization of trimehtylene carbonate and then blended with DPNR to evaluate its dispersibility and mechanical reinforcement. In the vulcanized DPNR/MCC-g-PTMC1, which introduced MCC/DPNR (28/72, w/w), the rubber exhibited stable mechanical properties compared to the conventional DPNR/MCC composite and the DPNR/MCC-g-PLLA composite grafted with the crystalline biodegradable polymer poly­(l,l-lactide) (PLLA). Specifically, the strain of DPNR/MCC-g-PTMC1 increased to 800%, while it was 750% the control samples of MCC/DPNR and DPNR/MCC-g-PLLA. The improvement of the stress at break maintain about 24 MPa, although it was around 22 MPa in the case of DPNR.

The influence of the dispersoid particle size variation on the morphological characteristics and mechanical properties of natural rubber (NR) with polystyrene island‐nanomatrix structure was investigated in this study. Fresh NR latex was incubated with urea and then processed through a series of centrifugation and redispersion steps at different forces to fractionate it into four low protein NR (LPNR) with average diameters of 238, 492, 721, and 1102 nm. Subsequently, graft copolymerization of styrene onto LPNR particles was carried out in the latex stage to prepare the NR with a polystyrene island‐nanomatrix structure. The relationship among particle size, morphology, and mechanical properties of the graft copolymer was analyzed. Transmission electron microscopy observations confirmed the formation of polystyrene island‐nanomatrix structure in each graft copolymer and revealed that the compactness of nanomatrix network increased as NR particle size decreased. The effect of nanomatrix network compactness on the mechanical properties was investigated through measurements of tensile properties, tear resistance properties, and viscoelastic properties, supported by digital image correlation strain mapping technology. A higher nanomatrix compactness was found to enhance mechanical properties and result in a more homogeneous distribution of strain.

Deterioration of fireproof polymer composite sheets equipped to elastomeric seismic‐protection isolators for buildings in use was investigated by various instrumental analyses after chemical treatments. The fireproof polymer composite sheet was prepared from polyisobutylene, various flame retardants, plasticizers, and so forth. Heat release tests with a cone calorimeter, fire resistance tests, and horizontal displacement tests were carried out for the fireproof polymer composite sheets. Furthermore, the fireproof polymer composite sheet after practical use was characterized in the present study. The sheet was found to have discolored during a regular inspection conducted in 14th year after the construction of elastomeric seismic‐protection isolators for buildings, which was immersed in rainwater collected in the pit for approximately 24 months. Rainwater‐unimmersed fireproof polymer composite sheets and the unused one were adopted as controls. Foamability, fire resistance, and heat insulating effect were significantly deteriorated after immersing into the rainwater. The deterioration of the foamability, fire resistance, and heat insulating effect was precisely investigated by Fourier transform infrared spectroscopy (FT‐IR), gas chromatograph–mass spectrometry (GC–MS), X‐ray diffraction (XRD) measurement, and electron beam microanalysis (EPMA) after extracting the rainwater‐immersed, rainwater‐unimmersed, and unused fireproof polymer composite sheets with methanol. Polyalcohol, pentaerythritol, and mineral oil as plasticizers were found to be leached from the fireproof polymer composite sheet by immersing in rainwater. The removal of pentaerythritol was also related to the deterioration of the foamability, fire resistance, and heat insulating effect since it played an important role as a forming agent.

This study proposes a novel strategy to enhance the mechanical properties of deproteinized natural rubber (DPNR) through the surface graft polymerization of protein‐mimicking N‐vinylamide monomers, which are N‐vinylformamide (NVF), N‐vinylacetamide (NVA), and N‐methyl‐N‐vinylacetamide (MNVA), initiated by oxygen radicals. Although N‐vinylamides generally exhibit low reactivity with oxygen radicals, selective grafting was successfully achieved via radical initiation at the polyisoprene surface, as confirmed by Fourier transform infrared spectroscopy and elemental nitrogen analysis. Tensile testing showed that approximately 70% of the modified samples surpassed the mechanical performance of high ammonia natural rubber (HANR), with the best‐performing sample achieving a tensile strength of 15.48 ± 0.64 MPa and strain at break of 1361 ± 29%. orphological analyses using TEM and AFM revealed the reformation of the nanophase‐separated “island‐nanomatrix” structure, which was absent in DPNR. This result highlights the importance of morphology in mechanical reinforcement. To our knowledge, this is the first report demonstrating N‐vinylamide grafting onto DPNR with the aim of replicating protein‐like functionality. This approach introduces a sustainable, water‐compatible method for functionalizing natural rubber by leveraging protein‐isomeric vinyl monomers and tailoring nanostructural design.

Rubbery soft polymer electrolyte membranes (PEMs) prepared from naturally occurring products are in high demand for the fabrication of flexible fuel cells as a multipurpose energy source to achieve a carbon-neutral society. This work describes the preparation of a rubbery soft PEM from deproteinized natural rubber (DPNR) by grafting-copolymerizing ethyl p-styrenesulfonate (SSEt) onto the surface of rubber particles in the latex stage, followed by hydrolysis with NaOH and cast film formation to construct a nanomatrix channel. The resulting rubbery soft PEM, a graft copolymer of DPNR and poly(p-styrenesulfonic acid) (DPNR-graft-PSS), is characterized by ¹H NMR spectroscopy, transmission electron microscopy (TEM), impedance analysis, and tensile testing. The hydrophobic rubber particles with a diameter of about 1 μm are well dispersed in the continuous nanochannel of hydrophilic poly(p-styrenesulfonic acid) with a thickness of about 10 nm that possesses a high proton conductivity, owing to an efficient proton transportation, which is beneficial for polymer electrolyte fuel cells. σ* is the proton conductivity per unit equivalent of sulfonic acid, which is distinguished from the proton conductivity, σ. The value of σ* for the DPNR-graft-PSS prepared with 1.0 mol/kg-rubber of SSEt is 2.6 (S/cm)/meq, which is approximately 1.4 times higher than that of the perfluorosulfonic acid membrane Nafion117, whereas its σ is lower. The apparent activation energy of DPNR-graft-PSS (3.2 kJ/mol) is lower than that of Nafion117, and its stress at break (6.9 MPa) is higher than that of DPNR. The high σ*, low apparent activation energy, and outstanding tensile strength of DPNR-graft-PSS can be attributed to the formation of the nanomatrix channel.