Increasing Wax Content Research Articles

MdDEWAX decreases plant drought resistance by regulating wax biosynthesis

Apple epidermal wax protects plants from environmental stresses, determines fruit gloss and improves postharvest storage quality. However, the molecular mechanisms underlying the biosynthesis and regulation of apple epidermal waxes are not fully understood. In this study, we isolated a MdDEWAX gene from apple, which localized in the nucleus, expressed mainly in apple fruit, and induced by drought. We transformed the MdDEWAX gene into Arabidopsis, and found that heterologous expression of MdDEWAX reduced the accumulation of cuticular waxes in leaves and stems, increased epidermal permeability, the rate of water loss, and the rate of chlorophyll extraction of leaves and stems, altered the sensitivity to ABA, and reduced drought tolerance. Meanwhile, overexpression or silencing of the gene in the epidermis of apple fruits decreased or increased wax content, respectively. This study provides candidate genes for breeding apple cultivars and rootstocks with better drought tolerance.

Effect of wax additives on asphalt rheological behavior as road paving material

In response to the growing demand for sustainable and high-performance roads, various asphalt additives have been developed and introduced to pavement construction. The increasing practice of warm mix in asphalt industry advances the usage of wax additives. However, the concern of wax content poses challenges to the application of wax additives in asphalt pavement via wet process. To address this concern, this study comprehensively investigates the influence of wax content on asphalt binder through rheological and chemical characterization. Specifically, three types of wax additives (Fischer-Tropsch wax, fatty acid amide wax and 64# paraffin wax) were selected at two dosages (2 wt% and 4 wt%) incorporating into four types of asphalt binder (virgin asphalt, SBS modified asphalt, asphalt rubber and high-viscosity & high-elasticity asphalt) to formulate various wax modified asphalts. Rheological properties were characterized to assess the engineering performance. Wax content and chemical mechanisms were characterized to investigate wax modification. Results show that incorporating wax additives enhances the engineering performance of asphalt binders but is difficult to meet wax content requirement. Fischer-Tropsch and fatty acid amide waxes are effective in improving rutting and fatigue resistance, whereas paraffin wax has an overall negative effect. Wax modification promotes the asphalt wax crystallization, leading to a further increased wax content and compromised low-temperature performance on asphalt binders, where modified asphalts can alleviate this adverse effect. Wax additives compromise low-temperature performance of virgin asphalt, but minimally impact modified asphalt. Careful wax content consideration is vital for virgin binders, while more flexibility of adjusting wax additive dosage is beneficial for enhancing overall of modified asphalt. This study is anticipated to prompt the understanding the influence of wax content on asphalt binder and benefit the industrial application of wax additives.

Co‐crystallization behaviors and thermo‐physical properties of SSPCM consisting of an extra low melt viscosity HDPE and paraffin waxes

AbstractShape stabilized phase change materials (SSPCMs) consisting of an extra low melt viscosity high‐density polyethylene (lv‐HDPE) and paraffin waxes (PW) were fabricated using a twin screw extruder. Thermal and mechanical properties of these composites were assessed. The latent heats (ΔH) of the SSPCMs fabricated were up to 78 J g−1. Co‐crystallization between lv‐HDPE and paraffin waxes increased with increasing wax content. Dynamic mechanical thermal analysis confirmed the paraffin wax having a higher melting point (H‐PW, Tm ranging from 56 to 58°C) plasticized the lv‐HDPE, decreasing both its crystalline content and melting temperature. Static mechanical testing, disregarding the form of deformation (tension, flexural, and compression), showed addition of paraffin waxes resulted in a diminution of all mechanical properties of lv‐HDPE, but the properties of the composites with H‐PW were good in comparison to those with a lower melting point wax (L‐PW, Tm ranging from 18 to 23°C). Evidences from Cole–Cole plots obtained from oscillatory rheology experiments showed there was no interaction between lv‐HDPE and H‐PW, inducing a heterogeneous blend in contrast to the more homogeneous lv‐HDPE/L‐PW composites.

Hydrate growth and agglomeration in the presence of wax and anti-agglomerant: A morphology study and cohesive force measurement

During deep-sea and ultra-deep-sea oil and gas exploitation, multiphase transmission lines are prone to be clogged by sediments produced by the various components in crude oils under extreme subsea conditions, such as hydrates, wax, resins, and asphaltenes. The pipelines face higher plugging risks when these deposits exist simultaneously. In order to elucidate the effects of wax and anti-agglomerants (AA) on hydrate growth and aggregation, microscopic morphology observation and cohesive force measurement of cyclopentane hydrate particles were conducted through a piece of equipment similar to the micromechanical force (MMF) apparatus. Results showed that in the low concentration of AA (0.05 wt%), hydrate particles experienced an approximately 10 % reduction in the profile area after converting water droplets to hydrate particles. Furthermore, the cohesive force between hydrate particles decreased from 8.57 ± 0.90 mN/m to 3.51 ± 0.43 mN/m as the AA concentration increased from 0.05 to 0.2 wt%. On the other hand, the presence of wax significantly altered the morphologies of hydrate particles. When wax coexisted with AA, the hydrate cohesive force was reduced by wax under low AA concentration (0.05 wt%) but increased under higher AA concentration. For a given concentration of AA, the hydrate cohesive force increased with the increasing wax content (from 0.1 to 0.3 wt%), indicating that wax crystals weakened the efficiency of AA, such as Span 80. Additionally, the effect of surface wetness of waxy hydrate particles on their cohesion was also investigated. The liquid bridge appeared between wet waxy hydrate particles, while the solid–solid contact existed between dry waxy hydrate particles. The cohesive force between dry waxy hydrate particles was smaller. Either liquid bridge or solid–solid contact that dominated hydrate cohesive force was affected by wax.

Investigating hydrate formation and flow properties in water-oil flow systems in the presence of wax

The coexistence of wax and hydrates will pose intractable challenges to the safety of offshore oil and gas production and transportation, especially for deep sea or ultra-deep sea reservoirs. Understanding the effect of wax crystals on hydrate formation, flow properties, and plugging risks of flow systems is imperative to the flow assurance industry. Experiments using systems composed of natural gas, water-in-oil emulsion with different wax contents, and AA (anti-agglomerant) were conducted in a high-pressure flow loop. For wax-containing systems, wax precipitates out during the induction period of hydrate formation. The induction time of hydrate formation decreased with the increasing wax content under the experimental conditions in this work. It was also found that the induction time for both wax-free and wax-containing systems increased with the increasing flow rate. The hydrate growth rate and the cumulative gas consumption were significantly reduced due to the existence of wax. Although the hydrate volume fraction of wax-containing systems was much smaller than that of wax-free systems, a stable slurry flow state could not be reached for wax-containing systems, the pressure drop of which gradually increased with the decreasing flow rates. The coexistence of wax and hydrates results in the deterioration of transportability and higher plugging risks. Based on the Darcy–Weisbach hydraulic formula, a dimensionless parameter was defined to characterize the plugging risk of flow systems with the coexistence of wax and hydrates. Additionally, regions with different levels of plugging risks could be evaluated and divided.

Morphology, phase diagram, and properties of high‐density polyethylene/thermally treated waste polyethylene wax blends

AbstractWaste polyethylene wax is thermally treated using a rotary evaporator to reduce unwanted components. Fourier transform infrared proves the absence of undesirable material. Wax is extruded with high‐density polyethylene (HDPE) at various loadings to study its morphology and final properties. Scanning electron microscopy and differential scanning calorimeter were employed to obtain the phase diagram showing the immiscibility of blends containing more than 20 wt% of wax. Due to the low melting temperature of the wax and its plasticating effect on HDPE, a decrease in melting temperature, enthalpy of fusion, and crystallinity with increasing wax content of the blend is observed. The phase diagram displays four possible phases depending on temperature and wax loading. Improved processability of HDPE/wax blends is demonstrated using complex viscosity curves. Han plots prove the miscibility of wax and HDPE in the melt state even at high concentrations of wax. HDPE/wax compounds have lower crystallinity, and wax particles, acting as weak spots, lower the elastic modulus, yield stress, and stress and strain at break as wax content increases. An increase in yield strain is observed due to the more effortless extension of HDPE chains at higher wax content. In 10 wt% of wax is accepted as the upper limit for wax incorporation into the HDPE matrix.

The overall crystallization behavior of polyethylene/wax blends as phase change materials for thermal energy storage: A mini review

AbstractThis review paper deals with the overall crystallization behavior of polyethylene/wax blends as phase change materials (PCMs) for thermal energy storage with the determination of their thermal properties. The addition of molten wax to the polyethylenes decreases the crystallization and melting temperatures of the blends. However, incorporating fillers to the polyethylene/wax blends can either decrease or increase the crystallization and melting temperatures of the composites depending on the filler type. The normalized enthalpy values of linear low‐density polyethylene showed no significant change when increasing the wax content. On the contrary, the normalized enthalpy values of the wax in the blends were lesser than that of pure wax and increased with increasing wax content. Since the wax in the blend had a lower crystallinity compared to pure wax, this influences its effectiveness as a PCM for thermal energy storage. The effect of different polyethylenes on the wax morphology gave rise to enhance phase separation when wax was blended to high‐density polyethylene as compared to the other polyethylenes. On the contrary, the effect of various waxes on the morphology of polyethylene resulted in different morphologies due to the molecular weight of the wax used and the structure of the polyethylene chain. The addition of fillers to the polyethylene (PE)/wax samples resulted in enhanced phase separation. The overall isothermal crystallization rate and the equilibrium melting temperature of PEs in the PEs/wax blends were depressed by wax addition due to the wax dilution effect.

Effects of waxes on hydrate behaviors in water-in-oil emulsions containing asphaltenes

In this study, the effects of waxes on carbon dioxide hydrate formation and dissociation in asphaltene-containing emulsions were systematically investigated using a high-pressure stirred autoclave equipped with an on-line viscometer. The results showed that the presence of waxes strengthened the inhibiting effect of asphaltenes on hydrate formation. Specifically, the induction time increased and the amount of formed hydrates decreased with increasing wax content in water-in-oil emulsion containing asphaltenes. The results indicated that waxes increased the viscosity of emulsions. It was observed that wax crystals dispersed in the bulk phase and got adsorbed at water–oil interface through the synergistic effect with asphaltenes. Furthermore, waxes inhibited the dissociation of hydrates in these emulsions. Both the gas emission rate and the average rate of hydrate dissociation decreased with an increase in wax content. The possible mechanisms were proposed to illustrate the effects of waxes on hydrate formation and dissociation in asphaltene-containing water-in-oil emulsions.

Identification of the SHINE clade of AP2/ERF domain transcription factors genes in Carica papaya; Their gene expression and their possible role in wax accumulation and water deficit stress tolerance in a wild and a commercial papaya genotypes

Climate change has resulted in alterations in temperature, soil salinity and droughts in many parts of the world. Carica papaya is one of the most important tropical fruits worldwide, although it is considered as a tolerant crop, water deficit stress affects its production. The aim of the present work was first to identify genes of the SHINE clade of AP2/ERF domain in the genome of C. papaya also, to characterize and compare the physiological performance, the total content of waxes and the expression levels of genes involved in wax biosynthesis in two papaya genotypes of contrasting tolerance (Maradol and Yuc1), when exposed to water deficit stress. Two genes (CpSHN1 and CpSHN2) were identified in C. papaya. It was clear that under water deficit stress, Yuc1 (a wild genotype collected at its center of origin), accumulated more cuticular waxes and had higher expression of both CpSHN1 and CpSHN2 genes than Maradol. This increased wax content might partly contribute to the higher water-deficit stress tolerance observed in Yuc1. Our results suggest that in response to water-deficit stress, CpSHN genes are involved in wax biosynthesis in C. papaya, allowing the accumulation of waxes (particularly alkanes). Both genotypes, showed tolerance to water stress, however the ability of Yuc1 to upregulate stress tolerance related genes faster than Maradol, might have favored an increased amount of waxes in leaves, contributing partly to its greater water-deficit stress tolerance than its commercial counterpart Maradol. The expression levels of CpSHN1 increased 30-fold in Yuc1 in response to water deficits and this was correlated with its superior ability to accumulate waxes. Although more studies are needed to further evaluate the functionality of CpSHN in water-limiting environments, our results suggest that CpSHN1 might be a good candidate gene to increase the water-deficit stress tolerance of this important tropical species.

Kinetic and rheological investigation of cyclopentane hydrate formation in waxy water-in-oil emulsions

Hydrates and waxes are supposed to coexist in the deep-water pipelines under suitable conditions of low temperature and high pressure. Understanding the effect of precipitated wax crystals on hydrate formation and rheological properties of hydrate slurry is crucial to the flow assurance in offshore petroleum production. In this work, a stress-controlled rheometer was used to carry out the rheological experiments for investigating the impact of wax crystals on hydrate formation and yield property of hydrate slurry. The effects of wax content and water cut on cyclopentane (CP) hydrate nucleation and growth were investigated in terms of the measured viscosity data. Log-normal distribution could well fit the probability density histogram of CP hydrate critical time. The logarithmic mean values of CP hydrate critical time decreased with increasing water cut but increased with increasing wax content in water-in-oil (w/o) emulsions. Semi-empirical models were proposed to describe the inhibitory effect of wax crystals on CP hydrate nucleation kinetics by considering the inhibition of mass transfer based on the Freundlich and Langmuir adsorption functions, respectively. Hydrate slurry viscosity rate showed the two-stage characteristics in wax-free w/o emulsions, while four stages could be clearly observed in waxy w/o emulsions. The maximum values of hydrate slurry viscosity rate and calculated hydrate effective volume fraction decreased with increasing wax content. Hydrate growth time was gradually extended as wax content increased. Furthermore, the measured yield stress and yield strain increased with increasing wax content at different water cuts, which was associated with the multiple effect of capillary bridge between hydrate particles, spatial network of wax crystals and coalescence of water droplets. At last, compared to the stress ramp rate, the influence of annealing time on yield stress was more significant.

Investigation of delayed formation of wax deposits in polyethylene pipe using a flow-loop

After the start of the flow in a home-built flow-loop, the thickness of a waxy layer deposited on a stainless steel (SS) test section was found to increase immediately, while deposition was delayed for around 4 h on a polyethylene (PE) test section. The radial thermal gradient, wax precipitation rate, radial diffusivity of wax, and shear stresses at the surface of the deposit layer were calculated, eliminating these factors as sources of different deposition behavior. However, the contact angles of oils containing precipitated wax crystals on PE surfaces were found to increase more with increasing wax content than those on SS surfaces. Consistent with this, while the wax contents of deposits were found to be around 18 wt % for both PE and SS pipes, the adhesion of the deposit on the PE surface was found to be much weaker than on the SS surface, as evidenced by the easier of removal of the deposit from PE than from SS pipes when heated in vertical orientation under gravity. These results point to pipe wall wettability as a significant factor in both initial growth of wax deposit, and ease of removal.

An Experimental Study on Evaluation of Factors Influencing the Viscosity and Viscoelastic Properties of Waxy Crude Oil

The influences of several operating factors on the viscosity of the Isfahan refinery waxy crude oil sample are studied through conducting some rheological shear rotational tests. The Taguchi design method is adopted to determine the impact of factors such as shear rate, temperature, cooling rate, wax content, and asphaltene content on the viscosity of the waxy crude oil. The results show that temperature with a contribution of 53.61% is the most influential factor. The wax content, shear rate, and asphaltene content have a contribution of 20.86, 14.75, and 3.11% respectively. The cooling rate does not have a statistically significant effect on the viscosity. The results of the rheological oscillatory tests confirm that the temperature and wax content change the viscoelastic properties of the waxy crude oil completely. An increase in the wax content from 12 to 22 wt.% raises the wax appearance temperature (WAT) from 19.1 to 34.9 °C and improves the gel point from 13 to 34.1 °C. By decreasing the temperature or increasing wax content, the viscoelastic nature of the oil sample changes from a viscoelastic fluid to a viscoelastic solid.

Influencing factors governing paraffin wax deposition of heavy oil and research on wellbore paraffin remover

Wax deposition is harmful to oil wells, especially for waxy heavy oils at low temperature. The influencing factors on wax deposition of heavy oil were studied and a kind of O/W emulsion type wellbore wax remover was investigated. The results showed that the wax deposition rate of Jinghe heavy oil increased with the increasing wax content and asphaltenes content but decreased with the increasing water content. The oil in water emulsion type paraffin remover was prepared and it showed both good wax dissolution and paraffin prevention ability and can save large quantities of solvent. The results of this study provides a possible way for waxy heavy oils to dissolve wax, to prevent wax deposition and reduce the viscosity of heavy oils by emulsification together, which is helpful to reduce the frequency of hot washing and enhance oil recovery for waxy heavy oils.

Expression of Arabidopsis SHN1 in Indian Mulberry (Morus indica L.) Increases Leaf Surface Wax Content and Reduces Post-harvest Water Loss.

Mulberry (Morus species) leaf is the sole food for monophagous silkworms, Bombyx mori L. Abiotic stresses such as drought, salinity, and high temperature, significantly decrease mulberry productivity and post-harvest water loss from leaves influence silkworm growth and cocoon yield. Leaf surface properties regulate direct water loss through the cuticular layer. Leaf surface waxes, contribute for cuticular resistance and protect mesophyll cells from desiccation. In this study we attempted to overexpress AtSHN1, a transcription factor associated with epicuticular wax biosynthesis to increase leaf surface wax load in mulberry. Agrobacterium mediated in vitro transformation was carried out using hypocotyl and cotyledonary explants of Indian mulberry (cv. M5). Mulberry transgenic plants expressing AtSHN1 displayed dark green shiny appearance with increased leaf surface wax content. Scanning electron microscopy (SEM) and gas chromatograph–mass spectrometry (GC-MS) analysis showed change in pattern of surface wax deposition and significant change in wax composition in AtSHN1 overexpressors. Increased wax content altered leaf surface properties as there was significant difference in water droplet contact angle and diameter between transgenic and wild type plants. The transgenic plants showed significant improvement in leaf moisture retention capacity even 5 h after harvest and there was slow degradation of total buffer soluble protein in detached leaves compared to wild type. Silkworm bioassay did not indicate any undesirable effects on larval growth and cocoon yield. This study demonstrated that expression of AtSHN1, can increase surface wax load and reduce the post-harvest water loss in mulberry.

Characterization of Morphology and Structure of Wax Crystals in Waxy Crude Oils by Terahertz Time-Domain Spectroscopy

The content, morphology, and structure of precipitated wax crystals are major factors affecting crude oil rheology. In this paper, model oils obtained by dissolving a realistic mixture of long-chain n-octacosane in diesel fuels were studied using terahertz time-domain spectroscopy (THz-TDS) and microscopy to gain insight into clusters composed of asphaltene and wax with increasing wax content. The fractal dimension was used for quantitative characterization of the morphology and structure of clusters in the model oils. From the measured absorption and extinction coefficients in the THz region, dynamic processes of the clusters in the model oils were analyzed and identified. The extinction coefficient in the THz region strongly depended on the dispersed and aggregated states of the asphaltene and wax crystals. These observations suggest that the aggregation state of the particles in model oils can be monitored with THz-TDS. In the future, THz-TDS technology may be used to effectively analyze particle dispe...

Thermal behavior of gamma-irradiated low-density polyethylene/paraffin wax blend

ABSTRACTThe thermal properties of low-density polyethylene (LDPE)/paraffin wax blends were studied using differential scanning calorimetry (DSC), thermogravimetric analysis (TGA) and melt flow index (MFI). Blends of LDPE/wax in ratios of 100/0, 98/2, 96/4, 94/6, 92/8, 90/10 and 85/15 (w/w) were prepared by melt-mixing at the temperature of 150°C. It was found that increasing the wax content more than 15% leads to phase separation. DSC results showed that for all blends both the melting temperature (Tm) and the melting enthalpy (ΔHm) decrease linearly with an increase in wax content. TGA analysis showed that the thermal stability of all blends decreases linearly with increasing wax content. No clear correlation was observed between the melting point and thermal stability. Horowitz and Metzger method was used to determine the thermal activation energy (Ea). MFI increased exponentially by increasing the wax content. The effect of gamma irradiation on the thermal behavior of the blends was also investigated at different gamma irradiation doses. Significant correlations were found between the thermal parameters (Tm, ΔHm, T5%, Ea and MFI) and the amount of wax content and gamma irradiation.

The effect of expanded graphite on the flammability and thermal conductivity properties of phase change material based on PP/wax blends

The study reports on the flammability, thermal stability, impact properties and thermal conductivity of shape-stabilized phase change materials based on a soft Fischer–Tropsch paraffin wax blended with polypropylene (PP). The blends were melt-mixed with expanded graphite (EG) up to 9 wt% to improve the thermal conductivity and flammability resistance of the material. The thermal stability and flammability results show an increase in thermal stability and flame resistance of PP in the presence of EG, with the flammability further increasing in the presence of wax, probably because of the smaller and better dispersed EG particles in the PP/wax/EG composite that gave rise to a more compact char layer. Although the thermal degradation mechanism did not change in the presence of EG, the EG particles retarded the evolution of the volatile degradation products. The storage modulus of the PP/wax/EG composite was lower than those of PP and PP/EG, and decreased with increasing in wax content because of the softening effect of the wax. The impact strength of the PP/wax/EG composites increased with increasing EG content in all the samples, but decreased with increasing wax content.

Structure and properties of phase-change materials based on high-density polyethylene, hard Fischer-Tropsch paraffin wax, and wood flour

Phase-change materials based on high-density polyethylene (HDPE), a hard Fischer–Tropsch paraffin wax (H1 wax), and alkali-treated wood flour (WF) were investigated. The blends and composites were prepared by melt-mixing. They were characterized in terms of their morphology as well as thermal, mechanical, thermomechanical, and water absorption properties. Although the scanning electron microscopy micrographs showed some evidence of intimate contact between WF and the HDPE matrix, there were poor filler dispersion and interfacial adhesion. The percentage miscibility of H1 wax in HDPE seems to have decreased with increasing wax content in the blends. A fairly strong affinity between the WF and H1 wax was noticed. There was plasticization of the HDPE matrix by the wax as well as inhomogeneity and uneven wax dispersion within the polymer matrix. The presence of H1 wax and WF influenced the crystallization behavior of the HDPE matrix. The incorporation of wax reduced the thermal stability of the blends and composites, but stabilized the WF. The H1 wax and WF differently influenced the viscoelastic properties of the HDPE matrix. In contrast to the blends where the tensile properties improved in the presence of wax, the composites showed poorer properties. An increase in wax content resulted in a decrease in water uptake by the composites. POLYM. COMPOS., 32:1155–1163, 2011. a 2011 Society

Thermo-mechanical Properties of Urea-based Pattern Molding Compounds for Investment Casting

Abstract Urea is a low cost material with thermal and mechanical properties suitable for use in investment casting pattern molding compounds. Conventional compounds are made by a “cooking” process wherein the urea is added to and dissolved in an aqueous solution of a water soluble polymer followed by evaporation of the water. Here we describe novel formulations based on either polyvinyl alcohol (PVOH) plasticized by glycerol or ethylene vinyl acetate (EVA) resins together with wax that can be prepared by a facile twin-screw compounding process. The thermo-mechanical properties of these compounds were characterized using differential scanning calorimetry (DSC), thermo gravimetric analysis (TGA), dynamic mechanical analysis (DMA) and three bend point tests. The PVOH-based molding compounds featured better mechanical properties than those based on EVA. Increasing the polymer content produced weaker but tougher molding compounds. Increasing wax content improved stiffness but resulted in a loss of toughness. The TG results showed that both compounds decomposed readily at elevated temperatures and left less than 3 wt.% ash at 800°C.

Phase change materials formed by uv curable epoxy matrix and Fischer–Tropsch paraffin wax

The use of an oxidized hard Fischer–Tropsch paraffin wax as phase change material in an epoxy resin matrix has been investigated. Samples were prepared by mechanical mixing of the wax powder with liquid resin at room temperature, followed by uv-curing of the samples. The results indicated the presence of spherical wax particles in the epoxy matrix, even after heating the sample to a temperature above the melting point of the wax, and cooling. At low wax contents the wax distribution was fairly heterogeneous, but the homogeneity improved with increasing wax content. The epoxy–wax interaction seems to be weak, and the presence of wax has an observable influence on the dynamic mechanical properties of the samples, especially above the melting point of the wax. Although the wax starts decomposing at a much lower temperature than the epoxy resin, the decomposition of the mixtures occurred in a single step.