Guayule Rubber Research Articles

Overexpression of tocopherol biosynthesis genes in guayule (Parthenium argentatum) reduces rubber, resin and argentatins content in stem and leaf tissues

Natural rubber produced in stems of the guayule plant (Parthenium argentatum) is susceptible to post-harvest degradation from microbial or thermo-oxidative processes, especially once stems are chipped. As a result, the time from harvest to extraction must be minimized to recover high quality rubber, especially in warm summer months. Tocopherols are natural antioxidants produced in plants through the shikimate and methyl-erythtiol-4-phosphate (MEP) pathways. We hypothesized that increased in vivo guayule tocopherol content might protect rubber from post-harvest degradation, and/or allow reduced use of chemical antioxidants during the extraction process. With the objective of enhancing tocopherol content in guayule, we overexpressed four Arabidopsis thaliana tocopherol pathway genes in AZ-2 guayule via Agrobacterium-mediated transformation. Tocopherol content was increased in leaf and stem tissues of most transgenic lines, and some improvement in thermo-oxidative stability was observed. Overexpression of the four tocopherol biosynthesis enzymes, however, altered other isoprenoid pathways resulting in reduced rubber, resin and argentatins content in guayule stems. The latter molecules are mainly synthesized from precursors derived from the mevalonate (MVA) pathway. Our results suggest the existence of crosstalk between the MEP and MVA pathways in guayule and the possibility that carbon metabolism through the MEP pathway impacts rubber biosynthesis.

An economic and environmental assessment of guayule resin co-products for a US natural rubber industry

Guayule (Parthenium argentatum) is a natural rubber producing desert shrub that has the potential to be grown in semi-arid areas with limited water resources. Numerous studies have examined the costs and environmental impacts associated with guayule rubber production. These studies identified the need for additional value from the rubber co-products, specifically the resin, for sustainable and commercial viability of the biorefinery concept. This study developed process models for resin-based monoterpenes, insect repellant, and adhesive co-products that are integrated with sustainability assessments to understand the commercial viability. A techno-economic analysis and cradle-to-gate life cycle assessment of these three different co-product pathways assumed a facility processing 66 tonnes/day of resin (derived from the processing of 1428 tonnes per day of guayule biomass) and included resin separation through co-product formation. Additionally, a fourth pathway was evaluated, combining the insect repellent and monoterpene process models to evaluate potential advantages resulting from their integration. The evaluation outcomes were integrated into an established guayule rubber production model to assess the economic potential and environmental impact of the proposed guayule resin conversion concepts. The minimum selling price for rubber varied by co-product: $3.64 per kg for monoterpenes, $3.48 per kg for insect repellent, and $1.90 per kg for resin blend adhesive. The resin blend adhesive co-product pathway had the lowest greenhouse gas emissions. These findings show a pathway that supports the development of a biorefining concept based on resin-based adhesives that can catalyze a US based natural rubber industry.

Replacement of Carbon Black with Coppiced Biochar in Guayule Rubber Composites Improves Tensile Properties

Natural rubber, sourced from Hevea brasiliensis trees mainly in southeast Asia, is a critically important resource for transportation, national security, and medical products, among other uses. The guayule shrub is a domestic alternative source of natural rubber that is emerging with advantages over Hevea since it is well-suited for many medical and consumer applications. Biochar is a sustainable form of carbon made from biomass that is a potential replacement for petroleum-sourced carbon black, the most common filler for rubber composites. The coppiced-wood species hybrid poplar (Populus × canadensis) and Paulownia elongata are both rapidly growing hardwoods that have shown promise as feedstocks for biochar that can be used as fillers in common rubber composites such as Hevea natural rubber, styrene-butadiene, and polybutadiene. In this work, poplar and paulownia biochars were used to partially replace carbon black as filler in guayule rubber composites. Guayule composites with up to 60% of the carbon black replaced with poplar or paulownia biochar had higher tensile strength, elongation, and toughness compared to the 100% carbon black-filled control. These composites would be excellent candidates for rubber applications such as gloves, belts, hoses, and seals, while reducing dependence on fossil fuels and Hevea natural rubber.

1081. Parthenium integrifolium L.: Compositae

SummaryThe North American Prairie plant, Parthenium integrifolium L. (Compositae: Heliantheae: Ambrosiinae) is described and illustrated. Related genera in the subtribe are commented on, as well as the better‐known species, P. argentatum A. Gray, the Guayule Rubber Plant, and infrageneric taxonomy within Parthenium L., in addition to the characteristics of the genus. Aspects of cultivation, propagation, pests and diseases and availability for P. integrifolium are also noted. A full synonymy of this rather variable species is provided, together with type citations, locations of known types, and related commentary. The distribution, habitat and ecology, phenology, common names and conservation status are stated or discussed, together with comments on usage, and the species' roots being used as an adulterant in preparations of Echinacea purpurea (L.) Moench.

Performance Assessment of Bioasphalt Mixtures Containing Guayule Resin as an Innovative Biobased Asphalt Alternative

Guayule resin was investigated through mixture to assess its role in the field performance. For performance comparisons, conventional asphalt, neat guayule, asphalt–rubber–guayule, and guayule–rubber binders were implied. Field-simulated lab mixtures were made to investigate the major distresses. Modified Lottman, rut, semicircular bending, and disk-shaped compact tension tests were used to assess stripping, rutting, fatigue, and thermal cracking resistances. Stripping and rutting susceptibilities were also assessed by Hamburg wheel-tracking test. The outcomes disclosed that when the modified Lottman test was used, guayule containing a 7% air content was more susceptible to stripping than that containing a 3.5% air content, resulting in tensile strength ratios of 40% and 71%, respectively. All investigated mixtures did not reach out the stripping inflection point under the Hamburg wheel-tracking criteria. Asphalt offered the worst Hamburg rut depth, which was 3.2 mm after 20,000 passes. Guayule-based mixtures perfectly resisted rutting as proven by the rut test. Guayule offered the worst rut depth of 6.3 mm, indicating a great rutting resistance. The guayule-based mixture had a high fracture toughness at intermediate temperatures. Guayule and guayule–rubber mixtures offered a critical strain energy release rate of 0.65–0.69 kJ/m2 compared to 0.46 kJ/m2 for asphalt. They, however, tended to possess low thermal fracture resistance (less than the threshold fracture energy, 400 J/m2). Conversely, a blend of 62.5% asphalt, 12.5% rubber, and 25% guayule offered 591 J/m2 at its performance grade low temperature (−16°C) and 409 J/m2 at −22°C compared to 429 J/m2 for asphalt at the later temperature, which represented the performance-grade low temperature of asphalt.

Guayule bagasse to make mycelium composites: An alternative to enhance the profitability of a sustainable guayule crop

Parthenium argentatum Gray, known as Guayule is recognized for its quality latex production. For this reason, the cultivation of this plant generates an important economic interest. Although this crop thrives in arid climates, its production has not been extended due to a high production cost per hectare compared to other rubber sources. To alleviate this difference in market prices and make Guayule rubber production competitive, several options have been proposed. One of them is the use of bagasse, which has been used to produce biofuels and refractory bricks, among other alternatives. Mycelium composites are a novel type of material with physical-mechanical characteristics similar to some types of expanded polystyrene with the additional advantage of being fully compostable. In this article, we successfully manufactured a Mycelium-based bio-composite using bagasse from guayule and a wild strain of Ganoderma curtisii by a simple pressed method, which is cost-effective, eco-friendly, and fully compostable. The composite G. curtisii/guayule showed excellent insulating ability with a K factor value of 0.0792 Btu/(h•ft•°F). In the same way, compressive strength and density values obtained were 0.740 MPa and 0.469 gcm−3, respectively. The composite G. curtisii/guayule manufactured in this work, has a low cost of manufacture and is environmentally friendly. Subsequent explorations for its use in various industrial applications like packing, building insulation, and interior design, could make more profitable the cultivation of guayule plant.

Bridgestone invests in guayule rubber

Bridgestone invests in guayule rubber

Tire maker Bridgestone invests in guayule rubber

Tire maker Bridgestone invests in guayule rubber

Science and Business Developments

Science and Business Developments

Economic and environmental sustainability assessment of guayule bagasse to fuel pathways

Guayule (Parthenium argentatum A. Gray) is a desert-dwelling crop that can produce hard rubber for tires and has the potential to help meet the water conservation needs of arid regions such as the Southwest U.S. Previous work has quantified the cost and environmental impact from guayule rubber production. However, establishing the economic viability of a domestic guayule industry requires identifying value-added products from the residual non-rubber guayule biomass, referred to as bagasse. Using guayule bagasse for bioenergy production is one potential solution, but the best pathway for thermochemical conversion of bagasse to fuels has yet to be defined. In this work, process models of pyrolysis and pelletization of bagasse are developed to inform a path to commercialization. A facility processing 200 tonnes of guayule bagasse per day is considered with a system boundary defined from biomass cultivation to fuel combustion. The materials and energy inventory results enabled the first comparative assessment of bagasse to fuels by concurrently performing techno-economic analysis and well-to-wheels life cycle assessment on both pathways. The minimum fuel selling price for the bagasse to fuels pathway was $0.076 per MJ ($9.26 per gallon of gasoline equivalent) and the minimum selling price of pellets from bagasse was $176 per tonne. This work compares the economic and life cycle results of both processes to make conclusions about the economic potential of bagasse and environmental impact of its conversion, areas to reduce production cost of biofuels, and potential for greenhouse gas emissions reduction compared with conventional fuels. In addition, the work identifies areas where future research may optimize production costs such that these fuels can be integrated alongside guayule rubber into a successful bioeconomy for the Southwest United States.

Irrigation effects on seasonal growth and rubber production of direct-seeded guayule

Understanding guayule’s response to environmental factors, such as location, soil type, drought stress, and seasonal growth variation is critical for irrigation management to maximize and estimate rubber and resin accumulation throughout the growing seasons. A study was conducted at two sites with different soil types (sandy loam soil at Maricopa, AZ and a clay soil at Eloy, AZ) to compare plant growth and rubber accumulation among different irrigation treatments during a two-year growing season. The above- and below-ground biomass, biomass growth, rubber/resin content, and rubber/resin accumulation were measured every other month from establishment to final harvest in well-watered treatments, which received 100% replacement of crop evapotranspiration (ETc) and irrigated with subsurface drip and furrow (denoted as D100 and F100, respectively), and compared to reduced irrigation treatments (D50 and F50), which received 50% replacement of ETc. Drip irrigation with high water input (D100) decreased root mass partition, but leaf, stem, and flower partitions were not significantly affected by irrigation treatment. Biomass yield was higher in the well-watered treatments as expected, while rubber and resin content were lower, indicating rubber and resin dilution by higher biomass. For all treatments, rubber and resin yield increased linearly over the two-year growing season. However, the rates of increase were different among the irrigation treatments. The D100 treatment had a higher rubber yield increase rate compared to F100 and D50 in sandy loam soil at Maricopa, while the D100 treatment had the lowest increase rate compared to the F100, F50, and D50 treatments in clay soil at Eloy. Top branches of guayule plants in the D100 treatment at Eloy lodged in the second year and likely contributed to lower rubber content and rubber yield in the treatment. The drip irrigation treatments D50 and D100 had higher water productivity for rubber yield at Maricopa. However, the D50 and F50 treatment had the highest water productivity for guayule rubber yield, while the D100 treatment had the lowest due to lower rubber content at Eloy. Root rubber content was 31–39% lower than stem at the two locations. This study indicates that rubber biosynthesis occurred in guayule year-round and that it is possible in clay soils to reduce irrigation without a significant loss in rubber yield.

Cycloartane- and Lanostane-Type Triterpenoids from the Resin of Parthenium argentatum AZ-2, a Byproduct of Guayule Rubber Production.

A total of 12 new cycloartane- and lanostane-type triterpenoids including 16-deoxyargentatin A (1), 16-deoxyisoargentatin A (2), 7-oxoisoargentatin A (3), 24-epi-argentatin H (4), 24-O-p-anisoylargentatin C (5), 24-O-trans-cinnamoylargentatin C (6), 16-dehydroargentatin C (7), 16,17(20)-didehydroargentatin C (8), isoargentatin C (9), isoargentatin H (10), 3-epi-quisquagenin (11), and isoquisquagenin (12) together with 10 known triterpenoids (13–22) were isolated from the resin of Parthenium argentatum AZ-2 obtained as a byproduct of Bridgestone guayule rubber production. The structures of new triterpenoids 1–12 and argentatin H (13), which has previously been characterized as its diacetate (23), were elucidated by extensive analysis of their spectroscopic data and chemical conversions, and the known compounds 14–22 were identified by comparison of their spectroscopic data with those reported. Of these, 13, 14, and 18 exhibited weak cytotoxic activity for several cancer cell lines.

Liquid guayule natural rubber, a renewable and crosslinkable processing aid in natural and synthetic rubber compounds

Liquid guayule natural rubber (LGNR) was produced by thermal degradation of guayule natural rubber and tested as a renewable alternative to naphthenic oil (NO) processing aid in natural rubber (Hevea and guayule rubber) and synthetic (styrene-butadiene) rubber composites filled with carbon black (CB). Processing oils are rubber additives commonly used to improve the processability of a compound. Most processing oils, like NO, are petroleum-based, and negatively impact the carbon footprint of the rubber industry. Moreover, these aids act as diluents that lower the mechanical performance of the resultant rubber products.The energy consumption of rubber compounding, mechanical properties and crosslinking networks of natural and synthetic rubber composites made with LGNR were characterized. LGNR effectively helped the compounds mix as demonstrated by 13–21% lower energy consumption compared to compounds mixed without processing aids. Moreover, unlike NO, LGNR acted as an active additive in the vulcanization reaction. Tensile strength, elongation at break, modulus at 100% strain and hardness increased when NO was replaced with LGNR in the compounds. The higher mechanical properties may be explained by additional crosslinking networks formed between LGNR and the rubber matrices and strong LGNR-CB interactions. LGNR, as a renewable processing aid, can address rising performance goals, and reduce carbon footprint for rubber products. In conclusion, LGNR provides the same benefits as conventional diluent processing aids, enhances the properties of the final material, and is produced from a renewable plant source.

Integrated techno-economic and environmental analysis of guayule rubber production

Persistent drought poses a significant risk to farmers in the southwest United States. Adopting drought tolerant crops that yield high value products will help mitigate this risk. One potential crop is guayule, which is known for its high natural rubber content. In this work, a process model was created to quantify all materials and energy required to cultivate, harvest, transport, and extract guayule rubber and co-products. This process model was used to enable the first concurrent techno-economic and environmental analysis of guayule. The techno-economic and environmental results include two scenarios: 1) a baseline scenario in which bagasse and resin are sold at predefined values and 2) an on-site heat and power scenario in which bagasse is combusted to generate heat and electricity. The result of the techno-economic analysis for the baseline scenario was a minimum rubber selling price of $3.08 per kg, with co-products of resin and bagasse being sold at $1.00 and $0.10 per kg, respectively. Baseline environmental results show that the largest impacts come from the use of fertilizers in agriculture and natural gas in the rubber extraction facility. The on-site heat and power analysis found an increased minimum rubber selling price of $4.07 per kg, but also a 61% decrease in global warming emissions. Discussion focuses on leveraging results to further the development of guayule by identifying high impact areas where future research may simultaneously reduce costs and environmental impacts.

A high-throughput quantification of resin and rubber contents in Parthenium argentatum using near-infrared (NIR) spectroscopy

BackgroundGuayule (Parthenium argentatum A. Gray), a plant native to semi-arid regions of northern Mexico and southern Texas in the United States, is an alternative source for natural rubber (NR). Rapid screening tools are needed to replace the current labor-intensive and cost-inefficient method for quantifying rubber and resin contents. Near-infrared (NIR) spectroscopy is a promising technique that simplifies and speeds up the quantification procedure without losing precision. In this study, two spectral instruments were used to rapidly quantify resin and rubber contents in 315 ground samples harvested from a guayule germplasm collection grown under different irrigation conditions at Maricopa, AZ. The effects of eight different pretreatment approaches on improving prediction models using partial least squares regression (PLSR) were investigated and compared. Important characteristic wavelengths that contribute to prominent absorbance peaks were identified.ResultsUsing two different NIR devices, ASD FieldSpec®3 performed better than Polychromix Phazir™ in improving R2 and residual predicative deviation (RPD) values of PLSR models. Compared to the models based on full-range spectra (750–2500 nm), using a subset of wavelengths (1100–2400 nm) with high sensitivity to guayule rubber and resin contents could lead to better prediction accuracy. The prediction power of the models for quantifying resin content was better than rubber content.ConclusionsIn summary, the calibrated PLSR models for resin and rubber contents were successfully developed for a diverse guayule germplasm collection and were applied to roughly screen samples in a low-cost and efficient way. This improved efficiency could enable breeders to rapidly screen large guayule populations to identify cultivars that are high in rubber and resin contents.

Potential Applications of Guayulins to Improve Feasibility of Guayule Cultivation

Guayule (Parthenium argentatum Gray) is an interesting alternative and renewable source of rubber/latex which has been used in the past. Guayule rubber and latex products are not available in the market largely because the raw material cost is higher than the current sources produced in South-East Asia and other tropical countries (Hevea brasiliensis). Guayule contains many other compounds whose joint exploitation could make guayule cultivation profitable, especially in semi-desert areas where cultivation of other crops is difficult or impossible. Guayulins A–D, sesquiterpene esters, appear to have some commercial promise. Despite being accumulated in relatively high concentrations (its majority representative, guayulin A, can account for up to 13.7% of the resin content of this plant, which itself ranges from 6%–12%), guayulins have received little direct attention from scientists. This review presents the current knowledge about the activity of these compounds and, based on known activities of similar compounds from other species, potential uses as fungicides, miticides and insecticides are suggested.

Transcriptomic and evolutionary analysis of the mechanisms by which P. argentatum, a rubber producing perennial, responds to drought

BackgroundGuayule (Parthenium argentatum Gray) is a drought tolerant, rubber producing perennial shrub native to northern Mexico and the US Southwest. Hevea brasiliensis, currently the world’s only source of natural rubber, is grown as a monoculture, leaving it vulnerable to both biotic and abiotic stressors. Isolation of rubber from guayule occurs by mechanical harvesting of the entire plant. It has been reported that environmental conditions leading up to harvest have a profound impact on rubber yield. The link between rubber biosynthesis and drought, a common environmental condition in guayule’s native habitat, is currently unclear.ResultsWe took a transcriptomic and comparative genomic approach to determine how drought impacts rubber biosynthesis in guayule. We compared transcriptional profiles of stem tissue, the location of guayule rubber biosynthesis, collected from field-grown plants subjected to water-deficit (drought) and well-watered (control) conditions. Plants subjected to the imposed drought conditions displayed an increase in production of transcripts associated with defense responses and water homeostasis, and a decrease in transcripts associated with rubber biosynthesis. An evolutionary and comparative analysis of stress-response transcripts suggests that more anciently duplicated transcripts shared among the Asteraceae, rather than recently derived duplicates, are contributing to the drought response observed in guayule. In addition, we identified several deeply conserved long non-coding RNAs (lncRNAs) containing microRNA binding motifs. One lncRNA in particular, with origins at the base of Asteraceae, may be regulating the vegetative to reproductive transition observed in water-stressed guayule by acting as a miRNA sponge for miR166.ConclusionsThese data represent the first genomic analyses of how guayule responds to drought like conditions in agricultural production settings. We identified an inverse relationship between stress-responsive transcripts and those associated with precursor pathways to rubber biosynthesis suggesting a physiological trade-off between maintaining homeostasis and plant productivity. We also identify a number of regulators of abiotic responses, including transcription factors and lncRNAs, that are strong candidates for future projects aimed at modulating rubber biosynthesis under water-limiting conditions common to guayules’ native production environment.

ENERGY ANALYSIS OF THE USE PHASE OF CONVENTIONAL TIRES COMPARED TO GUAYULE NR TIRES

ABSTRACT Guayule NR can be grown in the United States and offers a potentially more secure and sustainable alternative to the substantial Hevea NR that is imported from Southeast Asia. This paper presents the first rolling resistance and use-phase energy consumption estimates for guayule tires. The results of this study show that use-phase life cycle energy reductions can be achieved with NRs and that the rolling resistance coefficient (RRcnew) and reference service life (RSL) of the new tire are the critical parameters that pertain to energy and fuel efficiency. A tire's use phase accounts for approximately 86% of its life cycle energy consumption and thus is an important consideration in sustainability assessments. We calculated the use-phase energy consumption for two types of NR tires: a 100% guayule rubber tire and an experimental epoxidized NR tire. These two NR tires were compared against a conventional passenger tire made by Cooper Tire & Rubber Company. The ISO product category rules for passenger tires were used to determine energy consumption, while relevant data were measured from concept tires built in collaboration with Cooper Tire & Rubber Company. The results of this analysis showed that both experimental NR tires have improved use-phase energy consumption compared to conventional rubber tires. Although the epoxidized NR tire with low RRcnew consumes the least energy during the use phase, it is currently not being considered for commercial manufacture. The 100% guayule rubber tire shows a 6% reduction in energy consumption compared to the conventional rubber tire. Results of the sensitivity analysis showed a linear change in use-phase energy consumption with the relevant tire load and RRcnew and an inverse change with the average vehicle fuel efficiency and the RSL.

Downregulation of a CYP74 Rubber Particle Protein Increases Natural Rubber Production in Parthenium argentatum.

We report functional genomics studies of a CYP74 rubber particle protein from Parthenium argentatum, commonly called guayule. Previously identified as an allene oxide synthase (AOS), this CYP74 constitutes the most abundant protein found in guayule rubber particles. Transgenic guayule lines with AOS gene expression down-regulated by RNAi (AOSi) exhibited strong phenotypes that included agricultural traits conducive to enhancing rubber yield. AOSi lines had higher leaf and stem biomass, thicker stembark tissues, increased stem branching and improved net photosynthetic rate. Importantly, the rubber content was significantly increased in AOSi lines compared to the wild-type (WT), vector control and AOS overexpressing (AOSoe) lines, when grown in controlled environments both in tissue-culture media and in greenhouse/growth chambers. Rubber particles from AOSi plants consistently had less AOS particle-associated protein, and lower activity (for conversion of 13-HPOT to allene oxide). Yet plants with downregulated AOS showed higher rubber transferase enzyme activity. The increase in biomass in AOSi lines was associated with not only increases in the rate of photosynthesis and non-photochemical quenching (NPQ), in the cold, but also in the content of the phytohormone SA, along with a decrease in JA, GAs, and ABA. The increase in biosynthetic activity and rubber content could further result from the negative regulation of AOS expression by high levels of salicylic acid in AOSi lines and when introduced exogenously. It is apparent that AOS in guayule plays a pivotal role in rubber production and plant growth.

Eggshell improves dynamic properties of durable guayule rubber composites co-reinforced with silanized silica

Bio-renewable, inexpensive, reinforcing fillers for rubber composites are being developed to replace nonrenewable versions, in order to reduce carbon footprint of production. In this study, bifunctionally silanized silica (BSS), a commercial synthetic filler, was partially or completely replaced by micro-sized eggshell (ES), at three different loadings, in guayule (Parthenium argentatum, Gray) natural rubber (GNR) composites, and the dynamic mechanical properties, and durability (resistance to aging, fatigue and ozone) were characterized.Replacement of BSS with ES decreased the dynamic property of estimated rolling resistance, more than BSS by itself and, unusually, concomitantly increased the estimated wet grip of GNR composites. The composites filled with ES and BSS had comparable resistance to aging and fatigue. However, ozone resistance was greatest in composites made with a mixture of the two fillers. Durable GNR composites made with ES and BSS with improved dynamic mechanical properties, may support further expansion of the GNR industry.