What is it about?
This work is a comprehensive investigation into how different preservation methods affect natural rubber latex's (NRL) rheological behavior and microstructure. It contrasts the conventional ammoniated preservation system which employs ammonia and auxiliary hazardous preservatives (classified as Hazard Class 2.3 and regulated by OSHA’s 50 ppm exposure limit) with eco-friendly alternatives developed by AFLatex Technologies that effectively mitigate occupational and consumer hazards. The preservation of NRL is of utmost importance to prevent spontaneous coagulation and putrefaction. Traditionally, ammonia-based systems have been used; however, they pose significant health and environmental risks. The eco-friendly alternative not only circumvents these issues but also preserves the functional properties of the latex. In this study, we applied the Cross model, grounded in kinetic theory, to elucidate the material's shear-thinning and time constant behavior, which varies based on the structure. A proposed extended Krieger–Dougherty (K&D) model was then utilized to estimate the critical volume fraction a key parameter that aids in predicting both viscosity and the uniformity of the network formed during processing (controlled coagulation and film formation). Additionally, a Couette flow–based computational model was proposed to measure the effect of material properties (such as particle size and rubber density) on the critical volume faction driven by particle migration.
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Why is it important?
Health and safety improvements are among the leading factors driving this research. Moreover, integrating new technology into an older industry requires careful adaptation. Predicting key parameters such as viscosity and aggregation behavior by comparing eco‑friendly systems with well‑known ammoniated systems will be crucial for increasing industry adoption. Most importantly, this work advances the precise prediction of critical quality parameters, especially considering that NRL properties are subject to changes based on climate, crop variations, and species differences. Combining robust rheological models with sophisticated computational fluid dynamics (CFD) simulations holds promise for enabling real‑time predictions of complex behaviors in industrial processes, paving the way for more efficient and reliable latex production. From an economic perspective, this advancement can lead to cost savings in several areas. Improved formulations may reduce waste treatment costs and resource management challenges while potentially enabling the development of new or improved products.
Perspectives
The practicality of this work is evident in the use of strain amplitude measurements. This method can reveal a material’s transition from linear‑like to highly nonlinear flow, particularly in type IV overshoot responses. This overshoot behavior, often lacking a straightforward physical interpretation, is a crucial study area. While large amplitude oscillatory shear (LAOS) testing would provide richer insights, it is currently too resource‑intensive for routine or industrial use. Therefore, we turned to simpler viscometric methods, specifically shear rate ramps, to gather data for fitting to the Cross model. This approach allowed us to obtain robust estimates of non‑Newtonian regimes. By extending these results with the K&D model, we could predict how particle aggregation and viscosity evolve near critical volume fractions. Beyond volume fraction, parameters such as particle size and density—both of which can fluctuate with local climate conditions and tree species, can be readily varied in a CFD model proposed to predict changes in viscosity and particle aggregation. Implementing CFD at an initial screening stage, whether during rubber collection or formulation design, enables rapid estimation of critical volume fractions and viscosity shifts before committing to more extensive physical tests. This computational shortcut thus offers valuable, early-stage guidance for optimizing latex preservation processes, addressing the complexity of natural variability and the need for practical, efficient solutions.
Oliyad Dibisa
University of Wisconsin Madison
Read the Original
This page is a summary of: Comparative rheology and microstructure analysis of natural rubber latex with conventional and eco-friendly preservatives, Physics of Fluids, March 2025, American Institute of Physics,
DOI: 10.1063/5.0255679.
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Resources
Evaluation of an ammonia-free natural rubber latex adhesive
Ammonia-free NRL Industrial Adhesive exhibited superior mechanical properties when compared against resilient flooring adhesives and footwear adhesives. Additionally, the peeling strength of an ammonia-free 35% DRC with only cellulose (Office Adhesive) was compared to PVA-based Elmer's Glue and it was observed that the ammonia-free NRL adhesive outperformed Elmer's Glue by almost reaching four times the peeling strength of Elmer's Glue.
Environmentally safe preservation and stabilization of natural rubber latex in an acidic environment
Here, we present two novel liquid latex preservation and stabilization methods in an acid medium free of ammonia or other dangerous chemicals. The first method uses dodecyl benzene sulfonic acid to both stabilize and preserve the liquid latex, and the second uses ethoxylated tridecyl alcohol to stabilise and hydrofluoric acid to preserve the colloidal suspension. Both formulations result in rubber with superior mechanical properties, that is safe for the rubber plantation and industry workers, and with residues that no longer adversely affect the environment
Environmentally friendly ammonia-free preservation and stabilisation of natural rubber liquid latex
Latex is a fragile liquid which quickly decomposes in air shortly after its extraction from trees. Traditional means to avoid decomposition involve the use of additives, including ammonia, that are harmful to the environment and the people handling the material. A team at AFLatex Technologies in Portugal, led by Julio C Rodríguez and Professor Tim A Osswald, proposes two new routes to stabilising latex that don’t require the addition of harmful chemicals. These treatments also make latex suitable for the creation of adhesives whose efficiency outperforms those of current high-performance industrial adhesives.
Evaluating performance of traditional and eco-friendly latex preservatives
Rubber latex is widespread, used in everything from party balloons to medical equipment. As a natural product, latex needs to be treated with preservatives to keep it stable. Typically, these preservatives contain ammonia — which, though effective, can pose health risks.
Ammonia-free natural rubber latex photo-resin for sustainable 3D printing of highly stretchable and tough elastomers
at photopolymerization (VPP) is one of the most successful additive manufacturing modalities, offering high printing resolution and a wide selection of photo-resins for applications in aerospace, electronics, soft robotics, and biomedical devices. However, conventional photo-resins, primarily derived from fossil resources, present sustainability challenges. They often rely on short-chain oligomers that form brittle, dense polymer networks, limiting their performance in high-demand applications, especially for elastomeric materials. In this study, we developed an ammonia-free natural rubber latex-based photo-resin featuring an ultra-high molecular weight polymer with low viscosity (<10 Pa·s) and rapid curing speed (~11 s, corresponding to gelling point), making it highly suitable for VPP. The printed green parts underwent a two-step process of crosslinking and coagulation, resulting in semi-interpenetrating polymer networks with unique structural properties. Two curing intensities were investigated: 18 and 35 mW/cm2. We systematically investigated multiscale structure–property relationships using spin–lattice (T1) and spin–spin (T2) relaxation analysis via inversion recovery and Carr-Purcell-Meiboom-Gill. 18 mW/cm2 with 30 s of curing and drying resulted in two regimens of motion for Rubber polymer with intermediate crosslinking density and intermediate entanglements dominating the network. Also, 35 mW/cm2 with 30 s of curing and drying resulted in two regimes of Rubber polymer: however, one with a higher crosslinked and a mobile polymer phase. Optimized curing parameters enabled the fabrication of highly stretchable elastomers with 5–7.8 MPa tensile strengths and breaking strains of 750%–900%. These results highlight the potential of biomass-based photo-resins to advance sustainable 3D printing technologies. Furthermore, we demonstrated the feasibility of this formulation by printing complex geometries using a commercially available SLA printer.
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