Synthetic Fibers Research Articles

Future Prospects of Biodegradable Natural Fiber Composites: Innovations and Enhanced Performance in Roofing and Packaging Applications

This paper explores advancements in sustainable composite materials, focusing on biodegradable fibers, recycling innovations, and enhanced performance for packaging and roofing applications. With growing environmental concerns industries are shifting toward materials that reduce ecological footprints without compromising performance. Biodegradable fibers derived from natural sources such as hemp, jute, and flax have gained attention for their potential to replace synthetic fibers in composite manufacturing. These natural fibers offer environmental benefits including reduced carbon emissions, energy savings, and easier disposal. However, challenges remain in optimizing their mechanical properties to match conventional materials. Recycling innovations also play a critical role in achieving sustainability goals in composite manufacturing. Recent advancements in chemical and mechanical recycling processes allow the reuse of composite waste, reducing landfill dependency and resource depletion. Enhanced recycling methods improve material recovery and retain quality extending product life cycles. This research examines how these processes can be effectively applied in packaging and roofing, two sectors with high material demand and waste output. The study assesses the performance of sustainable composites in terms of durability, thermal stability, and resistance to environmental factors, critical for both packaging and roofing. Through a combination of experimental testing and case studies, this thesis demonstrates that sustainable composites can offer viable alternatives to traditional materials supporting a transition to greener construction and packaging solutions. This paper contributes valuable insights into the practical applications of biodegradable and recyclable composites paving the way for more sustainable material choices in industrial sectors

Optimization of the Properties of Eco-Concrete Dispersedly Reinforced with Hemp and Flax Natural Fibers

Dispersed reinforcement of concrete with various types of plant fibers is currently a fairly popular area in the field of construction materials science. The relevance of this topic is determined by the fact that the issue has not been studied on a large scale in comparison with concrete reinforced with artificial fibers, and the fact that these types of concrete meet the requirements of the Sustainable Development Goals. The purpose of this work was to evaluate the efficiency of using hemp fiber (HF) and flax fiber (FF) for the dispersed reinforcement of concrete, and to compare their efficiency and practical applicability in the construction industry. Before use, HF and FF were treated with a NaOH solution and stearic acid to increase their resistance to the aggressive alkaline environment of concrete. A total of 15 concrete compositions were made. The percentage of dispersed reinforcement for both types of fibers varied from 0.2% to 1.4%, with a step of 0.2%. The standard methods of mechanical testing and microscopy for investigation the properties of fresh and hardened concrete were applied. The optimum amount of HF in concrete was 0.6%, which provided an increase in compressive and flexural strength of 7.46% and 28.68%, respectively, and a decrease in water absorption of 13.58%. The optimum percentage of FF concrete reinforcement was 0.8%, which allowed an increase in compressive and flexural strength of 4.90% and 15.99%, respectively, and a decrease in water absorption of 10.23%. The results obtained during the experiment prove the possibility and effectiveness of the practical application of hemp and flax fibers in concrete composite technology.

Synergistic SERS Enhancement of Highly Sensitive and Reusable rGO-Ag-ZrO2 Thin Film Nanocomposite to Detect Synthetic Textile Dyes.

The textile industry is one of the main industries that benefited from the industrial revolution. Therefore, discharging of dyes from textile, paper, plastic, and rubber industries is inevitable. This colored wastewater prevents sunlight penetration and highly affects water sources. Cationic dyes such as Rhodamine 6G (R6G) and Methylene Blue (MB) obstruct plant growth, and most of these dyes are nonbiodegradable. Thus, cationic dyes are observed to be more toxic than anionic and reactive dyes. It is a great challenge to mankind to detect and remove these toxic dyes from the aquatic ecosystem. Surface-enhanced Raman spectroscopy (SERS) is an emerging cost-effective technique for the detection of any analyte at trace levels. Further, it is very important to design a highly sensitive SERS substrate to detect toxic dyes in lower concentrations. Owing to the high cost of coinage metal SERS substrates, semiconductor-based SERS substrates have gained attention recently. Though pure semiconductors have poor SERS activity, incorporating metal and graphene derivatives can further improve their surface and optical properties and make them highly sensitive SERS active substrates. In order to address this, we attempted to synthesize a reduced graphene oxide/silver/zirconia (rGO-Ag-ZrO2) hybrid thin film nanocomposite using the facile liquid/liquid interface method for the first time. The synergistic SERS effect of the rGO-Ag-ZrO2 substrate is highly sensitive and efficient to detect R6G until 100 pM concentrations. The multifunctional and versatile application of the rGO-Ag-ZrO2 substrate, such as reusability by the photodegradation method and the detection of an antibiotic drug, was also explored for the first time.

NEED BASED ADVANCEMENTS IN MAKING CONCRETE PAVEMENTS

Presently, innovations in concrete pavements are completely changing its design and construction. New-age concrete of compressive strengths more than 200 MPa also has very high tensile strength with or without the inclusion of steel/ synthetic structural fibers. Similar types of concrete mix proportions are referred in IRC: SP: 83-2008 under “Early Opening to Traffic” (EOT) concrete pavements, for maintenance of rigid pavement. Among other special concrete, Self-Consolidating Concrete (SCC) eliminates the need of mechanical consolidation and electrical energy at site and yields a required surface finish without segregation and undulation. Recently, it has been recommended in IRC:SP-62-2014 for construction of low volume concrete pavements in villages where skilled labour and mechanical/ electrical energy may not be easily available. Other similar technologies which are cost effective and environment friendly are given as under: i) Recycled concrete pavements, ii) Roller compacted concrete pavements (IRC:68-2005), iii) Ultra high performance concrete pavements(IRC:SP:76-2015), iv) High volume processed fly ash concrete pavements (IRC:SP:68-2005), v) Fibre reinforced concrete pavements (IRC:SP:46-2013), vi) Continuously reinforced concrete pavements- IRC:118-2015, vii) No joint sealant concrete pavements as per ACPA viii) Two lift concrete pavement/bonded concrete pavement (IRC:58-2015) ix) Sound reduction technologies x) Evaluation of Rigid pavement using falling weight deflectometer (IRC:117-2015) The paper thus describes new, cost effective, ecofriendly and practically need based advancements for making good quality concrete pavements and their evaluation for saving time and energy which are essential requirements for more infra-structure development with the creation of more jobs to the semi-skilled younger generation.

Investigation of the Characterisation Variances of Blended Non-woven Textiles: Banana, Flax and Recycled Cotton

Objectives: The study examines natural fibers' mechanical and thermal properties, specifically cellulose-based flax and banana fibers. Flax fibers are noted for their low density, high tensile strength, and rigidity, while banana fibers are recognized for their flexural strength and damping properties. However, treatments applied to these composites can negatively affect mechanical performance and surface integrity. The objectives of the research include comparing the properties of both fiber types, enhancing tensile strength through recycled cotton blends, evaluating the micro-structural characteristics of non-woven textiles for potential applications and sustainability, analyzing the elemental composition of nanomaterials, and investigating air permeability in relation to pore structure. Methods: The Energy-dispersive X-ray spectroscopy detector is incorporated into both transmission electron microscopy (TEM) and scanning electron microscopy (SEM) systems, which are employed for high-energy measurements. The analysis of the air permeability was carried out to evaluate how the pore structure affects its capacity to allow the passage of air/vapours. A testing analysis conducted by SITRA-South Indian Textile Research Association, Coimbatore utilized the Tex-test FX-3300-III, S/n:1198 Air permeability tester, following the guidelines of ASTM D 737-04 (2016) and IS 11056:2013, indicating that the static air permeability strength was notably enhanced. Findings: To determine if nanoparticles were present in the non-woven textiles, the microstructure of the non-wovens was examined at different EDS locations. Various elements were identified at each EDS site within the blended non-woven webs, along with variations in the elements' relative weights, atom counts, and K ratios. In an air permeability test, non-woven-1, made from banana-recycled cotton, exhibited higher values compared to non woven-2, which consisted of flax-recycled cotton. Novelty and applications: This research focuses on creating sustainable textiles by blending varying proportions of banana, flax, and recycled cotton, presenting an alternative to traditional single-fiber textiles. The study also introduces textile waste regeneration as a novel concept. Through the EDS Spots system, elements are identified and compared, offering valuable insights for potential technical applications. Permeability analysis evaluates the pore structure of the composite nonwoven materials, which are recognized as superior substitutes for synthetic glass fibers due to their elevated cellulose content. Their outstanding mechanical and thermal properties make them highly suitable for technical applications in the construction and automobile sectors. Keywords: Banana/flax fibers, Recycled cotton, Energy-dispersive X-ray spectroscopy, Air permeability, SEM-Scanning electron microscopy

Synthetic Fiber Content Measurement in Concrete Using Neutron Thermalization

The macro-fiber content in concrete cast in the field is critical to achieving the desired toughness properties and performance of the concrete structure. Currently, there exists no standard method to determine the polymer fiber content of hardened concrete. A nuclear density/moisture gauge was used on hardened concrete pavements with and without polymer fibers. Polymeric fibers are composed primarily of carbon and hydrogen. Since these elements are substantial neutron thermalizers, the neutron count detector on the nuclear gauge is sensitive to changes in the fiber content. The effects of hydrogen and carbon present in the unreinforced concrete itself were subtracted out by taking readings on specimens without fibers. Polymer fiber volume had a clear and statistically significant effect on the neutron readings. This effect was found to be linear and the polymer fiber volume of hardened concrete could be quickly and accurately be determined. The proposed non-destructive and in-situ test procedure can provide useful information for engineers conducting forensic failures and provide a method of quality assurance for determining the as-built polymeric fiber content of fiber reinforced concrete structures.

Distribution of Fiber-Reinforcement in Thin Concrete Overlays

The spatial distribution and orientation of fibers in concrete materials can be linked with the measured fracture performance of the fiber-reinforced concrete (FRC). For FRC pavements, the improved toughness performance is used for adjusting the structural design and expected service life of the pavement. The prediction of toughness performance and pavement serviceability can be improved with a better characterization of fiber dispersion in the concrete pavement. In this research study, a flowable fibrous concrete (FFC) mixture was developed containing a synthetic macrofiber at a volume fraction higher than found with existing thin concrete pavements. This FFC mixture is anticipated to have greater toughness induced by more fiber alignment in a thinner (5 cm thickness) concrete inlay pavement. Quantification of synthetic fiber dispersion and alignment in the FFC mixture was made using x-ray computed tomography and imaging analyses. The influences of placement technique and proximity of cast or mold surfaces were investigated and found to impact the fiber spatial distribution and orientation. The image analysis revealed that the number of fibers crossing any vertical plane, which increased for FFC placed under directional flow, was directly related to the measured fracture performance. Fibers were verified to have the desired alignment, allowing more fibers to become engaged in crack opening resistance, when the FRC was placed as a thinner pavement layer and therefore resulting in a more cost-effective use of FRC for pavements.

The mechanism of microplastic fibers release in a front-loading washing machine

Microplastic fibers (with a diameter of less than 5 mm) generated by synthetic textiles during the washing machine laundering process are considered to be one of the primary sources of pollution in both water and land environments. This study aimed to investigate the impact of novel combinations of washing parameters on the release of microplastic fibers. A wall-mounted drum washing machine was chosen as the subject of research in order to comprehensively examine the influence of washing conditions on the release of microplastic fibers during the washing process. The results showed that the length of shedding microplastic fibers were between 300 and 400 µm. The diameter of the shedding microplastic fibers was 13 ± 1 µm. High amounts of water and high load can lead to an increase of fiber microplastic release. Abrasion between fabrics influenced the release of microplastic fibers according to the movement of the fabric, which could affect fiber directional migration conditions. The findings on microplastic fibers release will help in the development of better front-loading washers.

A Review of Fatigue Performance of Fiber Mixture with Concrete

The fatigue performance of fiber reinforced concrete is a research hotspot in the field of civil engineering. This paper systematically reviews the related research. The fatigue performance of fiber reinforced concrete is different from that of ordinary concrete because the internal structure is changed by the addition of fiber. Different kinds of fibers have different effects on fatigue performance. Steel fiber can enhance the toughness of the matrix, effectively hinder crack propagation, and significantly improve the fatigue life. Synthetic fibers have obvious effects in inhibiting early microcracks, and the mixed use of the two will produce complementary phenomena. Among them, steel fiber has the greatest improvement in the mechanical properties of concrete, with an average increase of 30.5%-41.7%. Glass fiber and synthetic fiber have improved the mechanical properties of concrete, with an increase of 10.5%-14.6%. Among them, the improvement of mixed fiber is significantly higher than that of single fiber and the mechanical properties are improved by about 45%-59.2%. The existing research mostly focuses on experimental analysis, numerical simulation is relatively less, and the research on long-term fatigue performance in practical engineering applications is still insufficient. In the future, it is necessary to strengthen multi-scale research, improve numerical models, and deeply explore its fatigue behavior in complex environments, so as to provide more solid theoretical support for engineering applications.

Hybrid Composite With Natural and Synthetic Fibers in the Rehabilitation of Reinforced Concrete Structures

Hybrid Composite With Natural and Synthetic Fibers in the Rehabilitation of Reinforced Concrete Structures

Enhancing Polylactic Acid (PLA) Performance: A Review of Additives in Fused Deposition Modelling (FDM) Filaments.

This review explores the impact of various additives on the mechanical properties of polylactic acid (PLA) filaments used in Fused Deposition Modeling (FDM) 3D printing. While PLA is favored for its biodegradability and ease of use, its inherent limitations in strength and heat resistance necessitate enhancements through additives. The impact of natural and synthetic fibers, inorganic particles, and nanomaterials on the mechanical properties, printability, and overall functionality of PLA composites was examined, indicating that fiber reinforcements, such as carbon and glass fibers, significantly enhance tensile strength and stiffness, while natural fibers contribute to sustainability but may compromise mechanical stability. Additionally, the inclusion of inorganic particulate fillers like calcium carbonate improves dimensional stability and printability, although larger particles can lead to agglomeration issues. The study highlights the potential for improved performance in specific applications while acknowledging the need for further investigation into optimal formulations and processing conditions.

Exploring Innovative Approaches for the Analysis of Micro- and Nanoplastics: Breakthroughs in (Bio)Sensing Techniques.

Plastic pollution, particularly from microplastics (MPs) and nanoplastics (NPs), has become a critical environmental and health concern due to their widespread distribution, persistence, and potential toxicity. MPs and NPs originate from primary sources, such as cosmetic microspheres or synthetic fibers, and secondary fragmentation of larger plastics through environmental degradation. These particles, typically less than 5 mm, are found globally, from deep seabeds to human tissues, and are known to adsorb and release harmful pollutants, exacerbating ecological and health risks. Effective detection and quantification of MPs and NPs are essential for understanding and mitigating their impacts. Current analytical methods include physical and chemical techniques. Physical methods, such as optical and electron microscopy, provide morphological details but often lack specificity and are time-intensive. Chemical analyses, such as Fourier transform infrared (FTIR) and Raman spectroscopy, offer molecular specificity but face challenges with smaller particle sizes and complex matrices. Thermal analytical methods, including pyrolysis gas chromatography-mass spectrometry (Py-GC-MS), provide compositional insights but are destructive and limited in morphological analysis. Emerging (bio)sensing technologies show promise in addressing these challenges. Electrochemical biosensors offer cost-effective, portable, and sensitive platforms, leveraging principles such as voltammetry and impedance to detect MPs and their adsorbed pollutants. Plasmonic techniques, including surface plasmon resonance (SPR) and surface-enhanced Raman spectroscopy (SERS), provide high sensitivity and specificity through nanostructure-enhanced detection. Fluorescent biosensors utilizing microbial or enzymatic elements enable the real-time monitoring of plastic degradation products, such as terephthalic acid from polyethylene terephthalate (PET). Advancements in these innovative approaches pave the way for more accurate, scalable, and environmentally compatible detection solutions, contributing to improved monitoring and remediation strategies. This review highlights the potential of biosensors as advanced analytical methods, including a section on prospects that address the challenges that could lead to significant advancements in environmental monitoring, highlighting the necessity of testing the new sensing developments under real conditions (composition/matrix of the samples), which are often overlooked, as well as the study of peptides as a novel recognition element in microplastic sensing.

The Current State-of-the-Art of the Processes Involved in the Chemical Recycling of Textile Waste.

The textile industry's rapid growth and reliance on synthetic fibres have generated significant environmental pollution, highlighting the urgent need for sustainable waste management practices. Chemical recycling offers a promising pathway to reduce textile waste by converting used fibres into valuable raw materials, yet technical challenges remain due to the complex compositions of textile waste, such as dyes, additives, and blended fabrics.

A review on enhancing the properties of lime concrete using rubber-based synthetic fibers

A review on enhancing the properties of lime concrete using rubber-based synthetic fibers

Comparison of Lichen and Moss Transplants for Monitoring the Deposition of Airborne Microfibers

Interest in using lichens and mosses to monitor airborne microplastics is growing, but few studies have thoroughly compared their effectiveness as biomonitors. Here, we directly compare the ability of lichen and moss transplants collected from a rural area to accumulate microfibers (MFs) and Potentially Toxic Elements (PTEs) under the same deployment conditions. Transplants (n = 60; triplicates for both lichen and moss) were co-deployed on tree branches across a range of urban exposure sites (e.g., commercial and residential areas and urban parks) for 77 days in Siena, Italy. The results showed that both biomonitors accumulated similar amounts of MFs, in terms of counts and on a mass basis, but when expressed on a surface area basis, lichens showed significantly higher values. Irrespective of the metric, lichen and moss MF accumulation data were strongly correlated. In contrast, there was no correlation between MFs and PTEs, suggesting that their sources were different. MFs accumulated by lichen and moss transplants were dominated by polyethylene terephthalate (PET) and polypropylene polymers, suggesting that the main source of airborne MFs is synthetic textiles. Our results suggest that both lichen and moss transplants can be effectively used as low-cost monitors of atmospheric MFs in urban areas in support of the sustainable development goal of clean air.

Numerical Modelling of Hybrid Polymer Composite Frame for Selected Construction Parts and Experimental Validation of Mechanical Properties.

This article is a numerical and experimental study of the mechanical properties of different glass, flax and hybrid composites. By utilizing hybrid composites consisting of natural fibers, the aim is to eventually reduce the percentage usage of synthetic or man-made fibers in composites and obtain similar levels of mechanical properties that are offered by composites using synthetic fibers. This in turn would lead to greener composites being utilized. The advantage of which would be the presence of similar mechanical properties as those of composites made from synthetic fibers along with a reduction in the overall weight of components, leading to much more eco-friendly vehicles. Finite element simulations (FEM) of mechanical properties were performed using ANSYS. The FEM simulations and analysis were performed using standards as required. Subsequently, actual beams/frames with a defined geometry were fabricated for applications in automotive body construction. The tensile performance of such frames was also simulated using ANSYS-based models and was experimentally verified. A correlation with the results of the FEM simulations of mechanical properties was established. The maximum tensile strength of 415 MPa was found for sample 1: G-E (glass-epoxy composite) and the minimum strength of 146 MPa was found for sample 2: F-G-E (G-4) (flax-glass-epoxy composite). The trends were similar, as obtained by simulation using ANSYS. A comparison of the results showed the accuracy of the numerical simulation and experimental specimens with a maximum error of about 8.05%. The experimental study of the tensile properties of polymer matrix composites was supplemented with interlaminar shear strength, and a high accuracy was found. Further, the maximum interlaminar shear strength (ILSS) of 18.5 MPa was observed for sample 1: G-E and the minimum ILSS of 17.0 MPa was observed for sample 2: F-G-E (G-4). The internal fractures were analyzed using a computer tomography analyzer (CTAn). Sample 2: F-G-E (G-4) showed significant interlaminar cracking, while sample 1: G-E showed fiber failure through the cross section rather than interlaminar failure. The results indicate a practical solution of a polymer composite frame as a replacement for existing heavier components in a car, thus helping towards weight reduction and fuel efficiency.

A Review on Mechanical Improvements and Environmental Benefits of Rice Husk Reinforced Polymer Composites

The continuous advancement in science and technology necessitates the development of engineering materials tailored to specific requirements and cost-effective with minimal energy consumption. Consequently, there has been a surge in research dedicated to the fabrication of composite materials. Traditionally, the inclusion of synthetic fibers like glass or carbon is a common practice to reinforce composites and impart the necessary properties. However, their slow biodegradability poses environmental concerns, driving interest in natural fibers as substitutes. Rice husk (RH), a byproduct of rice milling, stands out as one of the most abundant agricultural wastes globally. Incorporating rice husk into polymer matrices is cost-effective and offers improved mechanical properties, low density and biodegradability etc. Various surface treatment techniques like alkaline treatment, benzoylation, acetylation and silane treatment etc., are explored to improve the integration of rice husk with base polymer, thereby imparting improved mechanical properties to composites. The present article provides an extensive review of literature regarding the prospective use of rice husk as reinforcement in various polymer matrices, highlighting primarily the mechanical attributes of polymer composites. Existing literature spanning the last 20 years has been extensively explored to analyse the impact of utilizing RH on the mechanical attributes of RH-reinforced polymeric materials. Future research directions are also highlighted, emphasizing the need for further exploration and optimization of rice husk-based composites for diverse industrial applications.

The Characterization and Development of Kenaf and Graphene Nanoplatelets in Polylactic Acid Composites

Kenaf fiber is in high demand due to the need for lightweight composites, particularly in the automobile industry and occasionally for interior building materials. Its remarkable strength and low density are the main causes of this. The use of natural fiber as a bio-composite material is limited because it is less heat resistant compared to synthetic fiber. To bolster the mechanical robustness of kenaf composites, graphene nanoplatelets (GnP) are incorporated as a supplementary reinforcing agent. Numerous studies have explored the mechanical properties of composites made from natural fibers and polymer matrices, with the recent market introduction of polylactic acid (PLA) polymers as biodegradable matrix options for biocomposites. The objective of this study is to determine the effects of incorporating graphene fillers on the tensile and flexural properties of PLA, kenaf, GnP composites. Hot pressing compression moulding is employed to fabricate the composite samples consisting of varying compositions, ranging from 95% PLA, 5% kenaf, and 0% GnP to 80% PLA, 15% kenaf, and 5% GnP. The result shows that adding 5% Graphene Nanoplatelets as a reinforcing filler will enhance the tensile strength and tensile modulus up to 18.2% and 53.2% respectively. While the flexural strength and flexural modulus enhanced up to 46.1% and 53.2% respectively. Besides that, DSC analysis shows that adding GnT does not alter the thermal properties of the composite with a melting point of 161.5 ℃. Overall, the results confirm that the addition of graphene improves the mechanical properties of the composites. It is suggested that further research should investigate the optimal ratio of GnP, kenaf, and PLA composition in order to achieve the optimum mechanical properties so that this composite has the potential to be used in various applications.

Molecular Dynamics Study of the Structure and Mechanical Properties of Spider Silk Proteins.

Spider silk is renowned for its exceptional toughness, with the strongest dragline silk composed of two proteins, MaSp1 and MaSp2, featuring central repetitive sequences and nonrepetitive terminal domains. Although these sequences to spider silk's strength and toughness, the specific roles of MaSp1 and MaSp2 at the atomic level remain unclear. Using AlphaFold3 models and molecular dynamics (MD) simulations, we constructed models of MaSp1 and MaSp2 and validated their stability. Steered molecular dynamics (SMD) simulations showed that MaSp2 resists lateral stretching, whereas MaSp1 exhibited better extensibility. During longitudinal stretching, MaSp1 formed cavities, whereas MaSp2 stretched uniformly. Hydrogen bonds involving GLN and SER in MaSp1 were strong, whereas those involving Tyr307 were prone to breakage, potentially weakening toughness. These results indicate that MaSp1 enhances extensibility, whereas MaSp2 imparts greater toughness. This study offers key molecular insights into spider silk's strength, informing the design of artificial fibers.

Examining the hidden dangers: Understanding how microplastics affect pregnancy.

Microplastics, a fast-growing environmental concern, play a crucial role in developing the major pollution crisis that affects nearly the entire surface of the planet. Microplastics are tiny particles, measuring less than 5mm which are ubiquitous, in occurrence, and found in a wide array of products including plastic packaging, synthetic textiles, seafood, fruits, vegetables, salt, sugar, bottled water, and even personal care products. The presence of microplastics in our environment and the potential adverse health effects they may cause have made them a significant perturbation in recent years. Pregnancy is a potentially life-changing experience that entails several apprehensions and new responsibilities for women. For expectant mothers, it is imperative to be aware of the implications of microplastics during pregnancy. One threatened concern is the potential transfer of microplastics across the placenta, which could expose the developing fetus to these particles. Although research on the impact of microplastics on pregnancy is still in its early stages, preliminary findings indicate potential risks that expectant mothers should be aware of. The timing of exposure during pregnancy may play a significant role in the potential risks associated with these tiny particles. In this review, we will delve into the topic, exploring how microplastics enter the body and the potential mechanism by which they pose risks to pregnancy outcomes.