Polymer Moulded Bottle Assembly - Report Example

POLYMER MOULDED BOTTLE ASSEMBLY By Student’s name Course code and name Professor’s name University name City, State Date of submission Introduction The need to have flexible packaging solutions has over years seen the development of various engineering approaches. The inception of polymer bottles manufacturing in the past 25 years provided a breakthrough in the packaging industry that required attractive and portable packaging especially in the food and beverages industry. The market for plastic bottles rather commonly known as Polyethylene Terephthalate (PET) has since grown steadily to achieve a great market share in packaging solutions due to its reliability and recyclability. According to Encyclopaedia Britannica, Inc. (2014), PET is a stiff and strong and synthetic fibre of polymer family that can be extruded to form reliable forms of disposable beverage bottles. Ethylene glycol liquid that is obtained from ethylene can be stored in a crystalline form which when heated together with catalysts such as terephthalic acid and ethylene glycol results to a molten substance that can be solidified later to manufacture plastic packaging bottles and other related goods. The increased levels of innovation has seen improvements in the formation of PET structures in that the carboxyl groups have been made to react forming ester groups that can serve as reliable chemical links between the long polymer chains that form a PET molecule. The basic reaction of this formation is shown in the chain reaction below; Some of the manufacturing processes that are highlighted in this report for formation of PET bottle include extrusion blow moulding process and injection blow moulding among others. The process of transforming an idea into a design is also put into consideration among the environmental impacts that this material poses to the ecology. Design of Polymer Moulded Bottles The design process of a PET bottle begins right from product development stage to the finishing stage which requires a product to have attributes such as flexibility, superior clarity, ease of handling, light weight, shatterproof and barrier excellence. Brandau (2012) insists that in developing an effective PET bottle product, the design phase must be strategically approached. CAD systems are deployed in such scenarios in order to come with a fit of the requirements that may be required by the client. For example the bottle in the assignment page belongs to the detergent manufacturing company Aerial®. This bottle was meant to carry a certain amount of detergent say one litre and has to have an appealing look to the clients. It is at this stage that this bottle shall be instilled with those attributes that matter to the end user who in this case is the consumer. The use for which the product is designated for, matters a lot even to the type of finishing that shall be attributed to it. Apart from detergents, for example, PET bottles are also used for mineral water, dairy products, fruit juices and tea among others. It is therefore the mandate of the manufacture to put these characteristics together with the consumer approach and regulatory measure (recyclability) in mind on order to come up with a comprehensive product. The type of manufacturing processes is also put in mind while designing polymer moulded bottles for purpose of proper resource utilisation and efficacy of production. The processes to which the end product shall be imposed on also matter in that the filling processes require different levels of strength in order to conform. Some of the processes involved include aseptic and hot filling. The bottle might also be exposed to quite a large amount of pressure – all this need to be put into consideration during the preliminary stages of design. The type of transportation process is also considered in order to instil the correct strength parameters onto the upcoming product. While conveyor belts might be used by one firm, another one using similar bottles may use a combination of articulated conveyor belts and gravity roller and so on. The speed of transport is also considered during the preliminary design stages so as to avoid differential failures once the product is put into use (Brandau, 2012). Figure 1: Tube filling mechanism – to be considered when designing PET bottles (Brandau, 2012). In as much as material affects the type of design to be effected, this shall be covered in the next section for a deeper analysis. The shape of the PET bottle to be manufactured also appears in the product design list with such shapes as multiple-foot base, still water base, hot filled product base and champagne base being presented for consideration. The type of neck that is required for a given product or trademark is also a major design influence. The types of necks that should be considered should be strong enough and as such still water necks, wild necks and plastic closure only are terms which have been basically designed for this approach. Without forgetting, the volume of product to be handled by a PET bottle should be considered as there are standard product packages for each manufacturer. For optimum performance, such specifications have been effected by a set of standards that do exist within the packaging industry to avoid extreme variances that may affect mould design and so on (Brandau, 2012). Apart from the aesthetic approach, it is important to consider some of the vital mechanical properties that should be put into consideration. Based on the preceding information, the top load which is of course the stacking level of a given industry should be given a priority. Safe working limits must be obtained for workability of a design – in such cases, the designer has to calculate the safety factor that is required for each bottle depending on the expected deformation levels. Internal pressure is also a key consideration in determining the mechanical properties of designated bottles. Due to additive packaging processes in which pressure and carbon dioxide is involved, it is important to determine the pressure levels that can be withstood by the chosen materials. Stability of handling is an important mechanical parameter to reflect on when designing; the safety factor should also put this into consideration. Stress cracking and barrier properties should be incorporated within existing and upcoming designs to avoid failure when using the item (Brandau, 2012). Material Selection The material selection process depends on several factors that are worth discussion in this article. Once the product has undergone a rigorous design exercise shown in the section above, it is important that these mechanical properties be matched to the existing materials in order to come up with the right product. Before settling on the final material to be PET some of the constraints involved must be highlighted by a design engineer as a matter of confirmation on which traits must be settled on unless the functionality is not extreme. For the product under consideration i.e. polymer bottle for Aerial® detergent packaging, the following requirements are set in place as per Ashby (2013) guidelines for eco-informed materials choice. According to this guidelines, the energy embodied by a given non-environmental friendly material such as polymers should be highly considered. The competing products are far much low when it comes to carbon dioxide emissions that producing PET bottles for the sake of this article shall not be considered. Therefore the constraint table 1 below shall not factor in the environmental aspect of PET bottles. This shall be covered in the last section to discuss environmental impacts of polymer moulded bottles in terms of recyclability and processing as per set carbon print regulations. Table 1: Design requirements of a polymer moulded bottle Function Detergent storage and vending container Constraints Must be immune to corrosion Must be able to shape fast and easily Recyclability is a must as per prevailing conventions Objective Minimization of embodied energy Free variable Choice of material A general and self-explanatory checklist of materials properties and choices is shown in figure 2 below based on the design requirements. According to Curbell Plastics (2014), the choice of polymer materials is not only based on the general group characteristics but also other more specific rules and conventions. In the case of manufacturing a detergent bottle for Aerial®, the semi-crystalline thermoplastics are vividly the best in that they have a sharp melting point; the preforms shall not consume much power to heat and mould. These materials are also opaque and possess a good chemical resistance as well as a high resilience when it comes to cracking. Semi-crystalline thermoplastics materials are also good in wear resistance – a property that translates into high durability. However, the disadvantages cannot go unmentioned either as this material possess poor formability and difficulty of bonding through use of adhesives. Figure 2: Choosing a polymer moulded bottle material (Curbell Plastics, 2014). Manufacturing Processes Manufacturing processes involved in polymer moulded bottle manufacturing are divided into two broad areas namely; converting raw materials usually in powder and pellets form into a molten substance that can easily be shaped under normal circumstances to come up with preforms. This discussion shall be restricted to the forming or moulding process itself as opposed to the conversion of raw materials into preforms. The main processes of moulding covered in this section include extrusion blow moulding, injection blow moulding, stretch blow moulding and multilayer bottle extrusion. Extrusion Blow Moulding This method of moulding involves a round hollow tube that is formed by an extruding machine. The process is highly organised through an automated or semi-automated sequence in which all the processes such as bottle filling and labelling are incorporated. The blowing process involves hot compressed air and a mould cavity that is comprised of two halves whose parison eventually closes in on the mould cavity wall upon achieving the maximum volume. Once the moulds are cooled down, the machine opens up and the bottle is removed for trimming in order to facilitate for the next process which is of course binding. Figure 3: A schematic presentation of extrusion blow moulding (Groover, 2010) The binding process is carried out using the flash method in which the extruded parts are pinched against each other and ground to impart a good finish. Most resins that emerge from this process are reheated and re-used for the next batch of bottles that follow. Wall distribution is controlled through programming of the parison to be extruded in a manner that maximizes the materials being extruded between the mandrel and the die. This method is one of the most effective in that is applied by the packaging and beverage production industries (Groover, 2010). A schematic illustration of this process is indicated in the figure above for advanced understanding. Injection Blow Moulding The starting parison that is used in this process is injection moulded instead of being extruded. The sequence of this process is shown in the schematic diagram 4 below. As compared to the extrusion process the difference is not large. During the first stage of formation, the plastic is melted and injected into a mould cavity to form a preform. The preform is usually in a basic form such as a test tube but moulded with a screw finish at the top. This preform is then transferred to the second stage which involves blow moulding in which the core pin is expanded against a cold mould; though under protected circumstances. Figure 4: A schematic presentation of injection blow moulding (Groover, 2010). The injection blow moulding processes is subdivided into two groups i.e. one-step injection and two step injection moulding. In the case of one strep injection, the melted polymer is injected once to form a final shape while in the two step scenario, there must be formation of a preform prior to hot extrusion. The advantages of injection blow moulding are that the production rate is higher, greater accuracy is achieved, less waste is incurred and the scrap rates are lower (Groover, 2010). Stretch Blow Moulding The process of stretch blow moulding is a hybrid of both extrusion and injection moulding in that the preform parison is injection moulded after which it is transferred into the blow moulding cavity. Biaxial stretching then follows as a way of orienting and aligning the material molecules in order to achieve a perfected finish. The orientation process improves the ability to resist a gas barrier, increases the bottle stiffness, improves clarity, advances impact strength and finally reduces the weight of the product. For the case of stretch blow, the materials that can be used to come up with a perfect bottle include; polyvinyl chloride (PVC), PET and polypropylene. For the carbonated drinks and detergent storage, the most used material is PET which has also become synonymous of plastic bottles. Figure 5: A schematic presentation of stretch blow moulding process (Pimpex, 2012). Injection Moulding and Multi-Layer Bottles This process is used in manufacturing of bottles whose walls are tapered and possess a wide mouth such as seen in jars, vials and tubs. It involves material injection into a cavity that contains pressure which in turn forces the resin to conform to the body of the mould as seen in casting. The bottles that are produced through this method are evidently capable of holding a higher pressure due to uniform wall distribution and dimensional tolerance that is imparted during manufacture. The raw resin forms that can be used together with this process include styrene, polyethylene and polypropylene (O. Berk Company, LLC, 2014). The last and newest process that is involved in the manufacture of bottles is called multilayer extrusion which is also known as co-extrusion. Here, various bonds of plastic resin are layered to produce a heat stable hot filled bottle that is hermetically sealed when packaging food products. The central layer that is widely used for this multi-layered process is called EVOH (ethylene vinyl alcohol) based on its layer properties. Polyethylene and polypropylene have also been integrated within this method for outer layer formation because of the heat tolerance properties and clarity (O. Berk Company, LLC, 2014). Environmental Impact and Ethical Issues Associated with Polymer Bottles Polymer moulded bottles have been blamed for environmental degradation due to their inorganic state. Such degradation has been attributed to the mode of production of the raw materials that are commonly used for this process owing to production of high amounts of carbon dioxide and debris formation on the physical environment. The march to greener and sustainable solutions is being marred by continued production of such materials despite regulatory concerns being raised on the environmental impact that plastic bottles pose to the environment. It is indeed high time that the stakeholders in the packaging industries came up with measures to mitigate the impacts of this material on the environment as what has been done so far is not enough especially in developing nations. Other effects worth mentioning include carcinogenic chemical absorption by human bodies – an issue that is often ignored, marine life distinction due to floating polymer bottle debris and the fact that landfills consisting of plastic bottles seep into water aquifers causing poisoning of flora and fauna (Andrady, 2003). Below is a figure showing an example of the impacts that this material may have on the natural environment. Figure 6: Impacts of polymer moulded bottles land fills on the environment (Peters, 2013). Conclusion Production of polymer moulded bottles has revolutionised in terms of materials and process owing to continuous improvement efforts. This has led to the development of PET, PVC and polycarbonate materials among others. The main processes that have been developed for bottle manufacture are also discussed in a bid to acquaint with industrial processes. Some of the processes which this article expound on include extrusion blow moulding, injection blow moulding, stretch blow moulding and multilayer bottle extrusion. The schematic layouts are exhibited for some of the most used methods in order to create an accurate understanding of these processes. The environmental impacts of plastic bottles and ethical considerations are also mentioned to give brief knowledge on the requirements of the international conventions. List of References Andrady, A. L., 2003. Plastics and the Environment. New Jersey: John Wiley & Sons. Ashby, M. F., 2013. Materials and the Environment: Eco-informed Material Choice. 1 ed. Oxford: Butterworth-Heinemann. Brandau, O., 2012. Bottles, Preforms and Closures: A Design Guide for PET Packaging. 1 ed. Oxford: William Andrew. Curbell Plastics, 2014. Plastic Material Selection. [Online] Available at: http://www.curbellplastics.com/technical-resources/pdf/plastic-material-selection.pdf [Accessed 20 April 2014]. Encyclopaedia Britannica, Inc., 2014. polyethylene terephthalate (PET or PETE). [Online] Available at: http://www.britannica.com/EBchecked/topic/468536/polyethylene-terephthalate-PET-or-PETE [Accessed 20 April 2014]. Groover, M. P., 2010. Fundamentals of Modern Manufacturing: Materials, Processes, and Systems. 4 ed. New Jersey: John Wiley & Sons. O. Berk Company, LLC, 2014. Plastic Containers Manufacturing Process. [Online] Available at: http://www.oberk.com/packaging-resource-guide/containers-guide/plastic-containers-manufacturing-process.html [Accessed 24 April 2014]. Peters, S., 2013. Is Your Bottled Water Killing You?. [Online] Available at: http://naturalrevolution.org/is-your-bottled-water-killing-you/ [Accessed 24 April 2014]. Pimpex, 2012. Automatic Single Step Two Stations PET Injection Stretch Blow Molding (ISBM) Machines & ISBM Molds. [Online] Available at: http://www.plasticimpex.com/PlasticMachinery/PETInjectionStretchBlowMoldingISBMMachinery.htm [Accessed 23 April 2014]. Read More