Study On The Preparation And Properties Of Acorn-based Polymeric Composite Materials

With the growing shortage of crude oil resources in the world, considerable research efforts have been devoted to the formulation and characterization of new natural non-food resources based polymeric materials that can partly replace crude oil resources in the past decades. Acorn is an important natural starch source from wildlife forestry, and it serves as the seed for oak trees regeneration. There are about 900 known oak tree species throughout the world, of which, about 300 species can be approximately found in China, with an annual output of about 6.0-7.0 billion kg. While the content of amylopectin of acorn kernel is too high to be easily digested, furthermore, the large amount of low toxic tannin acid is difficult to be removed from acorn kernel. As a result, abundant acorn resources have being abandoned. Therefore, the development of non-food acorn resources posesses a potential marketing prospects.In the thesis,we firstly optimized the design of physical and chemical analysis of acorn starch, acorn kernel and acorn hull raw materials, and obtained a rudimentary knowledge of component content of these three kinds of raw materials to provide a basis for developing different usages. The results showed that acorn kernel contained 69.40 % starch content of which the amylopectin content was up to 59.01 %; the tannins content was 8.34 %. Acorn starch raw materials contained 87.21 % starch content of which the amylopectin content was up to 68.56 %; the tannins content of acorn starch raw materials was 5.67 %. In addition, a certain amount of soluble sugar, crude fat, crude fiber, and proteins were also included in acorn kernel and acorn starch raw materials. Acorn hull contained a large amount of cellulose, hemicellulose, lignin and tanninsof which the content of holocellulose mounted to 56.69 %; the content of acid-insoluble lignin was up to 32.45 %; the tannins content was 9.26 %. The results indicated that acorn kernel had a high content of starch, resulting in exploiting the acorn kernel-based materials according to those methods for preparation of starch-based materials. The components of acorn hull were similar to wood components so that it could be regarded as a superior materials for preparing wood plastic composites (WPC). The existence of amount of tannins in these three acorn raw materials could bring up a certain effect on acorn-based composites.Acorn starch-based wood adhesives were prepared with the method of gelatinization-oxidation-polycondensation. Thermoplastic acorn-starch (TPAS) and TPAS/Polycaprolactone (PCL) composites were prepared by utlizing a co-extrusion plasticized technique and a blending alloy technique with a twin-screw extruder.Acorn hull(AH)/Low Density Polyethylene (LDPE) composites and Acorn hull (kernel)/ Poly(1actic acid) (PLA) composites were also produced using the blending alloy technique. New foams were prepared by adopting Melamine-Urea-Formaldehyde (MUF) resin as raw materials, and acorn hull-filled type composite foams were also prepared with the co-foaming technique. Our major results and discovery were described as follows.1. Acorn starch-based adhesives and its composite adhesivesMain agents of acorn starch-based adhesives were prepared with the method of gelatinization- oxidation- polycondensation. The preparation technology was further optimized. MDI and RW-20 were added into the main agents in order to improve water resistance and mechanical properties. The results demonstrated that the addition of MDI and RW-20 could improve water resistance and tensile dry strength of plywood to varying degrees. While the water resistance time at 63 oC of main agents of adhesives modified by MDI were all below 60 min, the water resistance time with the RW-20 modification could last more than 180 min. The tensile wet strength approached to the level of national II plywood. The modifying mechanisms of MDI and RW-20 were investigated and described in this thesis. The gluing properties of composite adhesives of main agents of acorn starch-based adhesives and phenolic resin increased with an increase of phenolic resin content. The tensile wet strength exceeded the level of national II plywood. What's more, adding a certain amount of acorn starch into phenolic resin could improve its comprehensive properties. The product of phenolic resin filled with acorn starch can also reach the level of national type II plywood.2. Thermoplastic acorn-starch (TPAS)Thermoplastic acorn-starch(TPAS) was produced by blending acorn-starch and different plasticizers with a twin-screw co-extrusion plasticized technique.The effects of different plasticizers such as glycol, glycerol, monoethanolamine, iminobisetnanol and triethanolamine on mechanical, thermal and hydrophobic properties of TPAS were studied in this part. The results demonstrated that TPAS materials showed strong water and moisture absorption properties. The mechanical properties of TPAS materials varied with the type and content of plasticizer, content of plasticizer as well as the moisture absorption rate of TPAS. The results showed that these five different plasticizers had a better performance for plasticizing acorn starch as characterized by scanning electron microscopy (SEM) and X-ray diffraction (XRD) analysis. Meanwhile the native acorn starch granules were proved to transfer to a homogeneous continuous phase with the transformation of all crystalline structure. Dynamic mechanical thermal analysis (DMA) results revealed that the plasticized effect of TPAS materials also varied with different plasticized system. Thermogravimetric analysis (TGA) results showed that thermal stability of TPAS materials also varied with different plasticized system.3. Thermoplastic acorn-starch (TPAS)/Polycaprolactone (PCL) compositesThe binary composites of TPAS/ PCL were prepared by a blending alloy technique with a twin-screw extruder. The results showed that the glycerol compositing system had better mechanical properties than monoethanolamine and triethanolamine compositing system. The mechanical properties of TPAS-based were superior than thermoplastic acorn-kernel based. The mechanical properties of acorn starch-based were better than corn starch-based, while mechanical properties of TPAS/ PCL composites were greatly influenced by the moisture absorption property of composites. DMA results showed that there existed weak thermodynamic compatibility between blendings, which was further verified from SEM results. Composites had strong water absorption property, which can increase with the decrease of PCL content. But the GTPAS/PCL composites showed excellent mechanical properties. When the content of PCL reached 50 %, the composites can reach the tensile strength at 13.17 MPa, and the elongation at break at 1750 %, which was close to the pure PCL. Soil burial degradation analysis results showed the GTPAS/PCL composites had favorable biodegradation properties.4. Acorn hull(AH)/ low density polyethylene (LDPE) compositesThe binary bio-composites of acorn hull(AH)/ low density polyethylene (LDPE) were produced by a blending alloy technique with a twin-screw extruder. The mechanical properties of composites were decreased with an increase of acorn hull content. The effects of EAA, EVA and PE-g-MAH on composites were studied in this thesis. The results showed that PE-g-MAH was the best compatibilizer for AH/LDPE composite among these three compatibilizers. Compared with the mechanical properties of modifying composite without compatibilizers, the tensile strength increased by 77.6 %, flexural strength increased by 83.8 %, and anti-impact strength still remained at a level of 5.0 kJ/m2, when the content of PE-g-MAH was 5% under the condition of 50 % AH content. In addition, both EAA and EVA could improve the mechanical properties of composites at different levels. The SEM study of composites proved that the addition of compatibilizers improved the compatibility of AH powder with LDPE matrix. The testing results of DMA and DSC further confirmed that the addition of compatibilizers could significantly improv the compatibility between two phases and chang the properties of LDPE matrix materials.5. Acorn powder/ poly(lactic acid)(PLA) compositesThe composites were prepared with acorn powder and poly(lactic acid)(PLA) by using a blending alloy technique with a twin-screw extruder, followed by an injection molding processing or a hot-compression molding processing. The study of the composites microstructures showed poor adhesion between acorn powder and PLA matrix. The mechanical properties of acorn hull-based composites were slightly better than the acorn kernel-based composites. The impact resistance strength of reinforced acorn hull-based composites with steel fiber webs improved greatly in comparison with those without steel fiber webs. It reached at 1.51 kJ/m2. The hygroscopicity, mechanical properties, melt flow property and biological degradation property of composites were promising even though the composites had a 70 % content of acorn powder. AH-based composites showed flexural strength of 72.21 MPa, tensile strength of 48.56 MPa and impact resistance strength of 1.51 kJ/m2 when the content of acorn hull was 50 % Silane coupling agent KH-550, 4,4'- Methylenebis(phenyl isocyanate)(MDI) and PLA grafted with maleic anhydride (PLA-g-MAH) did not show obvious effect on mechanical properties of acorn hull-based composites. Results on thermal properties characterized by DSC, DMA and TGA showed that the addition of acorn powder significantly changed the properties of PLA matrix materials and affected the crystallinity (Xc%), crystallization temperature (Tc), glass transition temperature (Tg), melting temperature (Tm) and thermal decomposition temperature of PLA matrix.6. Acorn hull-filled type composite foamsNew flame-retardant foam materials were prepared by using Melamine-Urea- Formaldehyde (MUF) resin as raw materials. We then finely tuned and optimized a foaming technology, optimum solid content of MUF resin, optimum addition of surfactant, curing agent and foaming agent were determined, MUF foam apparent density– mechanical properties models were established. The results showed that there existed an exponential relation between mechanical properties and apparent density of MUF foam. Acorn hull-filled type composite foams were also prepared with a co-foaming technique. The flame-retardant property increased with an increase of addition of acorn hull, but the mechanical and anti-brittleness properties decreased greatly. Wood pulp fiber and J-100 crosslinking agent were added into pre-foaming system in order to improve the comprehensive properties of acorn hull-filled type composite MUF foams. The results showed that these two different physically and chemically modified foams improved the mechanical properties of composite foam at different levels. J-100 crosslinking modification improved the mechanical and anti-brittleness properties greatly. It was found that the mechanical properties of composite foam enhanced more than 10 times than the system without modification when little J-100 crosslinking agent was added into the pre-foaming system, and the relative loss powder rate has been 50 % lower, furthermore, the flame-retardant property slightly improved with the addition of J-100. FTIR and 13C-NMR analysis results showed the complexity of J-100 crosslinking modification mechanism.