While 100% hemp-based plastic is still a rarity,composite bioplastics made from hemp and other plant source are already in use.Though it is by definition a composite,in reference todimension and end-uses,researchers often use hemp plastics as distinguished terminology.Researchers have evaluated a range of biopolymers for their usefulness as bio-plastic materials,e.g.,cellulose,starch,collagen,casein,plant proteins.Some of the biopolymers for bio-plastics are polybutyrate,polycaprolactone,polylactic acid and polyhydroxalkanoate.Wheat gluten is one of the most important biopolymers due to its low cost and high content of hydrogen bonds in the film.Wretfors et al.developed short industrial hemp fiber-reinforced wheat gluten plastics and found that hemp fiber-reinforced wheat gluten plastics with 20% fiber content exhibit double tensile strength and ten times young’s modulus in comparison to the pure wheat gluten plastics.Wibowo et al.developed hemp fiber-reinforced bioplastics by using cellulose acetate and cellulose butyrate as bio-resin and revealed that hemp fiber-reinforced bioplastics show better mechanical properties than the non-renewable polypropylene-based hemp fiber-reinforced plastics.They are particularly suitable because of their strength,trimming trays for weed lightweight and environmental compatibility.China,as of now,produces a huge sum of hemp due to its current manufacturing infrastructure,maybe the potential exporter of hemp fiber for textiles.Hemp yarn is usually available in linear density ranging from 2.6 to 54 Nm.
Dry spinning method with a shorter drafting zone is preferred for hemp yarn production rather than the wet spinning method.Cotton is generally blended with hemp to reduce its spinning difficulties arising from pectin and lignin of hemp fiber.Fabric from this blended yarn shows better performance in moisture absorption,air permeability,anti-mold and antibacterial property,UV protection and antistatic properties.In a study,hemp noils were mixed with Uzbekistan cotton in rotor spinning.They obtained good quality yarn with up to 50% hemp fiber content.Hemp also proved its suitability for vortex spinning,and hemp/Tencel air vortex yarns show less hairiness and unevenness than that of the ring and siro spun yarns.Fabric knitted from this type of blended yarn shows significant improvement in lither hand and formability.Stankovic and Bizjak studied the performance of folded yarn in hemp knitted fabric and found noticeable improvement in air and water vapor permeability.In the Hemp/Cotton/Lyocell blended yarn with a higher ratio of hemp,moisture permeability and breath ability of knitted fabric increased though at the same time resistance to pilling and abrasion reduced.As the evenness property of hemp blended yarn with the increase of hemp fiber content is usually worsened,researchers suggested that spraying mist in the spinning frame for proper humidification improves the hairiness,evenness,and tenacity of the hemp/cotton blended yarn.Hemp fabrics are available,ranging from 270 to 540 gm.m 2 for general to technical use,and fabrics from blended yarn with hemp and wool,silk,or synthetic fiber are more usual.The first production of denim jeans and American flag from hemp is attributed to renowned manufacturer Levi Strauss.Protective clothing is made from a variety of natural fibers,but hemp has some specialty.Union fabric made from hemp yarn and cotton yarn is more rigid and shows good resistance to flammability,breaking strength,and pilling resistance.
Textile products manufactured from natural fibers are comfortable in warm weather though usually deficient in UV absorption,but fabrics from hybrid yarns exhibit better Ultraviolet Protection Factor.According to the Chinese Academy of Science,95% of ultraviolet rays can be blocked by hemp fabric.The alkali and enzyme treatment ensure lignin reduction and improve the surface smoothness and tensile properties of hemp fiber.Moreover,alkali solution increases the dyeing effect in the fabric made from hemp/cotton/polyester blended yarn.Liquid ammonia treatment can improve hemp fabrics’ hand and crease resistance.Fabric treated by sodium hydroxide with flame retardant compound improves the fire-retardant properties and fabric shrinkage.Enzyme treatment makes the hemp fabric softer,smoother,more elastic and highly leveled with minimal strength loss.When hemp is blended with wool,due to the increased amorphous are,it becomes less flammable.Antibacterial textiles have drawn a lot of interest in recent years because of their potential to reduce infection transmission in medical and healthcare environments.Hemp has antibacterial properties that are effective against many pathogenic bacteria .Alkaloids,flavones and saponins are active antibacterial constituents found in hemp fiber .Hemp fiber shows activity against Escherichia coli,Staphylococcus aureus and Pseudomonas aeruginosa.In addition,hemp has anti-mildew properties,and fabric produced from hemp is hypoallergenic.Due to being naturally anti-fungal and antibacterial,socks from hemp fiber are favored since they keep the feet odor-free.Cannabis sativa L.has been considered an important source of food,fiber and medicine for thousands of years.The hemp seeds are variable in size depending on the cultivar.
The actual seeds are enclosed in the pericarp,mostly known as a protective shell.Most of the seed consists of an embryo,mainly the two cotyledons,rich in oils,proteins,and carbohydrates,representing the plant’s nourishment during germination.After removing the bract,seeds are squashed by applying high pressure for manufacturing oil and a by-product named husk,which is also used for fertilizer and cattle feed.Hemp seed contains 30% protein,25% carbohydrate and 30% oil.Extraction of the hemp seed oil is carried out by cold pressing methods or applying organic solvent.After the first extraction,approximately 35% oil is left behind in the seed cake.Superior quality oil is obtained from the first extraction process.Cold-pressed seed oil is free from chemical contamination and contains more beneficial components like natural antioxidants that prevent aging-associated diseases like heart diseases,cancer and health problem.The hemp seed oil is a good source of two essential fatty acids: linoleic acid and alpha-linolenic acid.The omega-6 and omega-3 exist in the ratio of 3:1,comprising the most desirable oil content beneficial for human nutrition.Several studies reported that fatty acid is beneficial for health in preventing cardiovascular diseases,capable of reversing scaly skin disorder,inflammation,diabetes,and it reduces the risk of cancer and rheumatoid arthritis.The hemp seed oil also contains gamma-linolenic acid that is beneficial for preventing Osteoporosis .The Hemp seed is also a good source of nutrition for birds and fishes as it contains omega-3 and omega-6 in the optimum ratio.Traditional fossil fuels negatively affect the environment by polluting air and the environment during their manufacturing and use,thereby depleting the ozone level,one of the leading causes of climatic changes and global warming.As fossil fuel is gradually depleting,researchers are looking for sustainable renewable sources to produce bio-fuel,decreasing the dependency on fossil fuels.Hemp bio-fuel is considered an effective alternative to decrease the dependence on fossil fuels and reduce greenhouse gas emissions.
Nowadays,seeds and biomass are used as energy crops such as wheat grain for ethanol and rapeseed for bio-diesel.Accordingly,a variety of energy products can be produced from hemp,such as briquettes or pellets for heat production,biomass for electricity,or vehicle fuel e.g.,biogas from anaerobic digestion.In terms of the growth stage,biomass increases up to 50 cm/month due to numerous vegetative parts in the hemp plants.It demonstrates the ability to use solar energy and CO2 photosynthesis,strengthening its position in the group of energy plants that contribute to renewable energy.The digestible concentration of cellulose and hemicellulose is higher than any other crop making it suitable for bio-fuel.Although hemp bio-fuel exhibits superior oil quality with higher kinetic viscosity,some bio-fuels have been reported to increase CO2 emission if a complete well-to-wheel production pathway is considered.The construction sector is a major energy consumer,quantifying nearly 40%,of which 60% is employed for heating and cooling inside the space in developed countries.It contributes almost 32% of global energy demand and is liable for 30% of energy-based CO2 emissions.In Europe,the building sector emits nearly one-third of this greenhouse gas,whereas the construction material sector is responsible for 10% of worldwide CO2 emissions.With a view to intervention,scientists are searching for eco-friendly sustainable carbon-negative materials that would be used as a replacement in full or partial for carbon-positive materials for the construction and building sector.From ancient times,natural resources like plant or animal fibers,straw,etc.,have been and still are being tried to include in building materials where hemp is reported to be utilized in the 6th century AD.As a natural resource for building material,hemp-lime composite or hempcrete has drawn significant attention recently.It is a composite with mineral binder and plant-based aggregates ground to 5–40 mm long from hemp’s shiv or woody core.The properties of the composite depend on binder type,aggregate to binder ratio,size and porosity of the aggregates,and level of compaction.Notable uses of hempcrete started in early 1980,but as shown in Figures 4,5,6,7,8,9,hempcrete has proven acceptable as non-load bearing in walls,floors,and roof insulation due to its lightweight,good moisture buffering,trimming tray with screen thermal insulation,and acoustic properties.Hempcrete is produced with a mix of ground hurds or shiv,binders in different proportions and water.
Cement had been used as the binder,but currently,hydrated lime,hydraulic binders and pozzolanic binders like metakaolin are commonly used.Hydrated lime can set through the absorption of CO2 during carbonation,but the setting time is extended.Therefore,hydraulic and pozzolanic binders are added to quicken the setting.Varying the proportion within the composition consistent with needs,solid but lightweight and durable hempcrete are often produced ranging density from 200 – 800 kg m 3 to be used as wall,floor covering,or roof insulation.Hempcrete can be manufactured by spraying,molding,or manual mixing and tamping.It can be pre-manufactured or freshly made on the construction site.There are some reports of manufacturing it as blocks or hollow blocks or bricks.The compaction due to gravity is negligible though the spraying or projection method is reported to induce higher compaction with minor variation in density.Hemp shiv is a highly hydrophilic porous structure and shows strong capillary action,which ends up in the absorption of water up to nearly five times of its own weight that may often cause a lack of hydration.Therefore for proper slaking of the lime considerable amount of water is required in the mixture,which delays drying and setting time.In contrast,incomplete hydration of binders causes unsatisfactory mechanical strength.In addition to the excessive water,biological compounds especially sugars extracted from the shiv also delay the setting time of the composite and eventually lead to a reduction of mechanical strength of the material.Some researchers suggest that increasing binder hydraulicity may increase early strength development but it doesn’t affect ultimate strength regardless of binder type.The mechanical performance of hempcrete is relatively modest with very ductile elastic-plastic behavior in compression and tension having a dry density ranging from 200 to 800 kg m 3.Most researchers report that this lightweight porous material shows a compressive strength of less than 1 MPa though few pieces of literature claim it to range up to 3.6 MPa after 28 days with a variable Young’s modulus.Therefore,its favorable use is as non-load bearing walls with supporting frames or as finishing plasters with indoor and outdoor insulation properties when density is low,whereas it can also be used as floor or roof insulators with increased density.The causes behind the low mechanical performance of hempcrete have been studied extensively,and the factors identified for inadequate mechanical performance are its high porosity of about 80% in volume,the particle size of the aggregate,voids,too much hydrophilic nature of the aggregate,binder content and setting or curing process.In addition,the level of compaction,flexibility,imperfect particle arrangement,and recurring wetting-drying cycles also considerably affect the mechanical strength of hempcrete.
With a view to increasing mechanical performance,quite a number of research have been carried out which studied different aspects of hempcrete.Most of the researchers acknowledge that higher compaction causing the reduction of voids would increase its intended mechanical strength,but its thermal insulation and acoustic behavior are compromised.Relative humidity was also found to influence compressive strength.Curing at different RH was studied with a conclusion that best compressive strength was achieved with curing at 50% RH while curing at 75% RH and 98% RH resulted in worst performance,and low RH delays the setting of hydraulic binders.Increasing the binder content gradually leads to a lower strain level,although it had been suggested for producing panels or building blocks.Mechanical strength of hempcrete varies with the change of binder type; starch-based binders and cement resulted in higher compressive strength than lime binder.Among the Magnesium based binders that show greater compatibility with organic aggregates,magnesium phosphate cement showed increased mechanical performance.It was reported that using magnesium oxychloride cement can achieve two times stronger hempcrete without compromising density,thermal conductivity and carbon negativity.Cenosphere binder was also tried as an alternative to lime binders,but although it could retain its integrity at elevated temperature,a noticeable development in mechanical strength wasn’t observed.Mineralization of shiv with Al23 and Ca2 indicated achievement of four times compressive strength against non-mineralized hemp shiv with an acceleration of setting and hardening but the carbon negativity of the final product was not reported.Aggregate size can also affect the compressive strength in the long run since smaller particle sizes achieve better coating by binder than bigger particles.